Dealing With Traffic Congestion

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Dealing with Traffic Congestion:

An Interdisciplinary Perspective

Yu-hsin Tsai

The author is a postdoctoral researcher at the Institute of Transportation Studies, University of

California, Berkeley, CA 94720-1782. ([email protected]). He holds a Ph.D. degree in

Urban, Technological, and Environmental Planning from the University of Michigan, Ann Arbor.


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Dealing with Traffic Congestion:An Interdisciplinary Perspective

Roadway traffic congestion has been a common, irritating problem in many areas and

countries. This problem has occurred in both rural and urban areas, and developing

and developed countries. Time spent in traffic jam is widely considered as a total

waste and irreversible. Traffic congestion influences quality of life, economic growth

and environment. In the US the delay on urban freeways is expected to increase 360%

from 1985 to 2005 (Institute of Transportation Engineers 1989). This includes an

increase of more than 300 % in urban areas of the population of over one million, and

1,000 % in urban areas with population of less than one million. A variety of theories

and measures have been developed and intended to solve this problem by

transportation planners, urban planners and transportation economists. Different

combinations of these three groups of measures were applied to deal with congestion,

but unfortunately few cases show congestion was completely eliminated, in particular in

the long run. Experience suggests there seems no penicillinthat works for all

congestion cases.

The major purposes of this literature review paper are to understand the causes of

traffic congestion, the measures to dealing with traffic congestion from the perspectives

of transportation engineers, urban planners and transportation economists, and the

interactions between these groups. Through the analysis of the causes of traffic

congestion, this paper is intended to shed some light on the question Is traffic

congestion an unavoidable condition in urbanized areas in particular? The analysis of


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considered as a waste and had better be avoided. Indeed quality of driving constitutes

part of life quality, and hence mobility can be regarded as one goal of transportation.

Accessibility, however, is prevailingly believed by transportation planners as a major

goal of transportation (Johnson 1998), particularly where there are conflicts between

mobility and accessibility (see footnote 3). Since most demand for travel is derived from

the demand to accomplish certain social or economic activities, lower cost per trip,

instead of merely lower cost per mile is the objective of transportation service. Hence,

even within the scope of transportation, congestion can be an inevitable tradeoff for

better accessibility.

In the context of sustainable transportation6, new approaches to congestion

mitigation are required. In the 70s and 80s when interstate highway were

overwhelmingly developed (the era of the freeway could date back to the Interstate

Highway Act of 1956, traditional concerns of mobility and capacity dominated and the

movement of vehicles was the focus, rather than that of persons. The underpriced road

transportation in part due to lack of accounting for the externality of congestion and

environmental pollution, and subsidy (e.g., subsidy on single family housing) led to the

overuse of road network, urban sprawl, and air pollution. The experience in these two

decades suggested that Americans could not build their way out of congestion through

building highways (Transportation Research Board 1994). The desire for changes in

transportation policy due to recognition of these external costs of the road system and

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A sustainable transportation system is one that: 1) allows the basic access needs of individual and societies to be

met safely and in a manner consistent with human and ecosystem health, and with equality within and between

generations; 2) is affordable, operates efficiently, offers choice of transport mode, and supports a vibrant economy;

3) limits emissions and waste within the planets ability to absorb them, minimizes consumption of non-renewable

resources, reuses and recycles its components, and minimizes the use of land and the production of noise (The

Center for Sustainable Transportation 1997).


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was respected in Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA), and

is consistent with the spirit of sustainable transportation. The spirit of sustainable

transportation and ISTEA is expected to lead to more comprehensive balance7 among

society, economy and environment (The Center for Sustainable Transportation 1997,

World Bank 1996). In other words, in planning and assessing a transportation plan, all

benefits and costs (internal or external, direct or indirect) should be accounted for in the

decision making. In addition, the current transportation objectives per se, focus on

accessibility, rather than speed (or mobility) and capacity. This means movement of

persons rather than vehicles is of major concern. As a result, the throughput of

highways focuses more on persons than vehicles per lane per hour. An underlying idea

is to seek alternatives of capacity expansion, such as alternative transportation modes,

and land-use or economics based measures to improve accessibility, even at the cost of

lower mobility. For example, if the introduction of a mall with mixed land use, or a

pedestrian or bicyclist friendly environment could improve the residents overall

accessibility, but at the cost of reduced speed on road for motor vehicles (the former

could generate more traffic, and the latter could reduce road capacity), it could still be

an acceptable measure. Consequently, worsen congestion could occur but still be

acceptable if it is the result of the trade-off for better balance among society,

environment and economy, or for better overall accessibility. Though, highway

congestion is still an irritating condition, and the measures to calming congestion should

still be taken as long as they do not contradict sustainable transportation.

The influence of traffic congestion on transportation can be described through

7

The notion of balance is an ambiguous notion, and can be different from case to case. For example the cost of air

pollution could be valued less for the countries seeking economic growth. Hence their balance system may lean


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accessibility and mobility. For a highway system, better mobility can cause worse

accessibility; on the contrary better accessibility may result in worse mobility.

Transportation facilitates household activities by providing accessibility to different

activity locations, such as work places, schools, shopping malls, and recreation areas;

transportation also facilitates business and delivery for industries. Accessibility of an

individual location can be simply measured as the number of opportunity for travel

objective fulfillment that can be reached within an acceptable travel (Lomax and

Levinson 1997) or it could be measured as simply as cost per trip. Mobility is the ability

of people and goods to move quickly, easily and cheaply to where they are destined at

a speed that represents free-flow or comparably high-quality conditions (Lomax and

Levinson 1997). Mobility can be characterized as speed of movement, and can be

measured as cost per mile or mile per hour. Both the travel distance between the

locations of two activities (i.e., land-use factor) and the travel speed (i.e., transportation

factor) influence accessibility. A location with high accessibility to another place may be

constituted by close proximity or (and) high mobility (i.e. high speed). If the trip length is

fixed, higher mobility (i.e., higher speed) leads to higher accessibility (shorter travel

time). Under this condition, congestion will degrade accessibility. In contrast, higher

accessibility can reduce mobility if trip length is shortened because of changes of

locations. For example, the introduction of a local shopping mall into a community could

increase local traffic and lower the mobility, but the accessibility could be improved due

to shortened travel distance8

for shopping purposes. In sum, congestion is an issue

when obstructing accessibility (when travel distance is fixed); but congestion may be

more to economic development.


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more acceptable as a result of better accessibility.

Congestion has been defined differently by different persons or from different

perspectives. For travelers congestion is immobility (Levinson et al, 1997). The

traveler-based definition of congestion tends to be subjective since it is subject to their

internal rulers. This internal ruler is influenced by personal, socioeconomic and

temporal characteristics, so it is very likely that traffic congestion for one person may not

apply to another. For example, surveys were carried in Japan by different organizations

to define congestion, and their respective definitions are different to certain extent

(Hashimoto 1990). From the transportation perspective, congestion is defined as when

speed is lower than the speed at the design level of service9 in the U.S. (Pline 1992).

This kind of definition is more engineer-oriented though it was initially expected to take

users perception into consideration. Furthermore, the acceptable and unacceptable

congestion were initially developed in Congestion Management System regulation

(Federal Register 1993) . While the speed is still higher than at design level of service

but lower than free flow, it is called acceptable congestion. The unacceptable

congestion indicates there is a problem, and actions should be taken. From the

perspective of transportation economists, the definition of congestion is travel time or

delay in excess of that normally incurred under light or free flow travel condition

(Levinson et al, 1997). In other words, if increasing traffic flow increases travel time or

cost, there is congestion (Fisher 1996). This notion of acceptable and unacceptable

8

This credit of the generation of this idea is attributed to Levine, Jonathan.9

Expected speed of a road is influenced by two variables: designed speed and designed level of service (Pline 1992).

Designed speed is the maximum safe speed that can be maintained over a specified section of highway, which is a

design factor of the road. Different roads can have different designed speed. Level of service is defined as those

operational conditions within a traffic stream as perceived by users of the traffic facility. Levels of service are based

on density of the mainline traffic, and can be presented by Volume/Capacity. The design level of service can vary


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congestion can also apply to transportation economists definition. The unacceptable

congestion occurs when the travel cost or time is higher than the optimal point where

marginal cost equals marginal benefit (Appendix 1). For achieving maximum benefit of

society, this economics-based definition of congestion is chosen for this paper.

There seem some essential factors that contribute to the mystery of highway

congestion that few efficient measures can address. Traffic congestion is a reflection of

relative shortage of capacity (supply) in association with travel demand. The underlying

variables for this phenomenon are enormous and variant, some of which are avoidable

or treatable, others are unavoidable or hard to overcome. Experience suggests that in

existing congested urbanized areas, there seems to be no long-term solutions. This

paradox drives our curiosity toward the question Is congestion unavoidable and can be

regarded as a normal condition in urbanized areas? This research is not intended to

find the answer but to shed some light on this paradox based on previous researches.

From the perspective of travel demand, a group of essential variables is associated with

rapid growth in already urbanized areas, such as population and economy growth,

opposed to limited available land. These factors generally are regarded as natural trend

sin human society and as a given condition to planners. Another group of variables is

distribution associated (in terms of spatial and temporal dimensions) variables: over-

concentration of trip origins and destinations caused by land use and density, over-

concentration of trips on shortest routes, same periods of time and auto use. In practice,

traffic is not evenly distributed throughout a day or days, and on different routes. This

unevenly distributed traffic condition raises the issue about what is the optimal road

capacity (Hay 1973). Within a day, for example, adequate provision for all demands

by types of roads, where the road is located (Pline, 1992) and time of day or year (Lomax, et al, 1997).


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can only be ensured at the price of excess capacity during some other periods; while

alternative full utilization of capacity can be achieved only at the cost of leaving

demands unsatisfied. So if the capacity is set up and built at the point of financial

balance, then the peak-hours, days, or seasons are certainly facing congestion naturally.

From the perspective of highway supply, the capacity is decreased by unavoidable

conditions due to ambient environment, accidents and routine maintenance. A negative

spiral results as the space saved by congestion-alleviation measures other than pricing

strategies is usurped by the latent demand. Capacity-usurping effects involves triple

convergence10, swamping effect11 (Downs 1992), and change of other travel behaviors

(e.g., changes of destination, vehicle-occupancy and trip frequency). In addition,

congestion could be a result of good quality accessibility. Sometimes congestion is

unavoidable since high quality accessibility attracts more residents or industries. Also,

for the sustainable environmental reason a higher level of congestion is accepted.

Finally, users (or transportation engineers) definitions of congestion are likely to be

different from economists. That is, congestion felt by users might still be regarded as

acceptable by economists. All these variables point to highway congestion as a natural

social system condition. That is, as long as people follow the same clock or calendar,

seek the shortest route and most accessible locations, use the same, convenient travel

mode, then under limited resources, congestion seems unavoidable. Congestion could

be regarded as a factor for people to trade-off against other factors, such as economic

10

The triple convergence principle states that any large initial reduction of peak-hour travel times on a major limited-

access roadway will soon be offset by the subsequent convergence on that roadway of drivers who formerly (1) used

alternative routes, (2) traveled at other times, or (3) used public transit (Downs 1992).11

The principle of the swamping effect of rapid growth states that relatively small reductions in initial traffic

congestion in a rapidly growing metropolitan area will be fully offset within a few years by the arrival of more

people, jobs, and vehicles there (Downs 1992).


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development and sustainable environments. This, however, does not mean there is no

need to take an action to alleviate traffic congestion. Measures for calming congestion

that can improve the efficiency of road network, as well as achieving sustainable

transportation should still be taken.

Measures for Congestion Relief

Understanding the variables influencing miles traveled can help understand how

congestion relief measures affect traffic. Miles traveledis the quantity of road

consumed by travelers, which is determined by supply and demand for highway

altogether. Miles traveled is basically composed of personal and industrial trips. For

the personal trips, the function of miles traveled can be presented as:

Miles traveled = Population * Vehicle ownership12 (vehicle/population)* Travel mileage per vehicle13 (mile/vehicle)

The variables that influence population, vehicle ownership, and miles traveled per

vehicle are numerous, varied from time to time, and from place to place (Downs, 1992).

The underlying factors that influence these variables invlove population growth,

technology development, economic development, peoples preference and land supply.

For example, both population immigration and population fertility increases will increase

population. Increasing income may increase buying power of customers, and

12

The maximum vehicle/population is close to one (Downs 1992).13

Mile/vehicle is quite constant (Downs 1992).


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technology progress will lower car prices; as a result car ownership may increase. The

preference for driving alone is likely to increase miles traveled per vehicle. In terms of

industrial trips, population growth, economic development, and business style influence

miles traveled. Regarding business style, for example, home shopping and mall

shopping will create different miles traveled.

Most of the congestion alleviation measures are developed from three main

perspectives: economics, land-use and transportation engineering. The scope of

economic measures involve measures using price mechanism (Institute of Civil

Engineers, 1989); the land-use related measures focusing on changing land-use policy,

considered as one kind of demand contraction; the transportation measures contain

capacity expansion and demand contraction strategies. Evidently more than one

measure or measures of more than one perspective are applied. The measures derived

from these three different perspectives are based on different theories, require different

ways and different amounts of budget for implementation, have different degrees of

effects, and could cause different side-effects or problems. The following contain

details of the above measures, organized as capacity expansion (transportation-

engineer perspective), demand contraction (consisting of land-use- and transportation-

engineering perspectives), and pricing (transportation-economics perspective).

Capacity Expansion

Providing more road capacity is probably the most intuitive idea for alleviating

congestion. The variables that may influence the supply of highway are composed of


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temporary and permanent variables. Road capacity14 is the maximum number of

vehicles that can reasonably be expected to use the facility in a given time period under

prevailing roadway, traffic, and control conditions (Pline 1992). So a road capacity may

decrease if the roadway, traffic or control conditions gets worse. Roadway condition

contains geometric and design elements such as width of lanes, lateral clearance, and

horizontal and vertical alignment. These factors sometimes may affect speed or delay

time, while not affecting the capacity (United States, Federal Highway Administration,

Office of Traffic Operations 1994). Traffic condition includes vehicle types and lane or

directional distribution. Control condition includes traffic control, curb parking,

pedestrian ways, restrictions on vehicle types, ramp metering, posted speed limits, bus

stops, and parking regulation. All the above elements are design elements, most of

which will influence the design capacity of a road. On the other hand, some conditions

will reduce road capacity temporarily, and cause congestion irregularly. These

variables include road maintenance, car accidents, break-downs of electronic traffic

signals, and ambient environment including wet, snow covered pavement, darkness,

and fog.

Supply-side congestion alleviation measures are composed of three types: building

new roads or road expansion; improving roadway conditions, adjusting to traffic

conditions, and improving control system; in the case of temporarily reduced road

capacity, restoring the designed capacity. First, the most fundamental one is building

new roads or road expansion. This may not be suitable for developed areas since it is

hard and costly for land take. Besides, it needs longer time to build physical facilities

(Downs 1992). This method, however, could be welcome in areas intended to grow

14

The unit of road capacity is passenger car or passengers per hour per land (Transportation Research Board 1994).


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since it allows more traffic.

To increase the capacity of existing roads there are numerous methods of

improving roadway, traffic, and control conditions. About roadway condition, certain

design elements could be modified. For example, city streets can be upgraded by

widening their lanes. About improving traffic condition, for example, the numbers of the

lanes of two opposite directions could be adjusted according to traffic condition. About

control conditions, for example, Advanced Traffic Control(ATC) of Intelligent

Transportation System (ITS)15, automated highway16, and electronic turnpike system17

could smooth traffic flow, and hence the road capacity increases indirectly. Finally, as

for temporarily reduced capacity, the measures to bring it back to original capacity level

include: using roving response team or surveillance system to clear roadways quickly

after traffic accidents (Systems and Detroit 1996); improving process of highway

maintenance.

However, Downs (1992) argued that the congestion problem could only be relieved

temporarily, and in the long run the congestion problem would recur due to the

principles of triple convergence and swamping effect. Hansen (1995) provided

evidence that at the metropolitan level in U.S., 1.0 percent increase in lane-miles soon

induces an immediate 0.2 percent increase in traffic (Vehicle Miles Traveled) and 0.9

percent increase in traffic four years after. In fact, this represents the popular belief of

15

FAST-TRAC is an Intelligent Transportation System (ITS) that integrates advanced traffic control with a variety

of advanced traffic information systems through centralized collection, processing, and dissemination of traffic data.

(University of Michigan, ITS Lab 1996).16

The National Automated Highway System Consortium is constructing an automated highway demonstration

project on a stretch of interstate 15 between San Diego and Escondido, Calif. Equipment in and along the roadway

will be used to regulate the speed, steering and spacing of vehicles, creating a sort of automated train of cars and

eliminating the stop-and-go conditions of congested highways (ITS Online, 1999 )17

The E-Z Pass in the New York Metropolitan area is using electronic scanner as the car rolls through the tollbooth

(New York Time 1997).


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transportation planners that adding road capacity does little to decrease congestion

because of substantial induced traffic. In addition, in the U.K. most city centers are

congested but it is now generally accepted that solution is not new road building

(Younes 1993). Nevertheless, Singapore, for instance, is still planning to build 225

lane-kilometers (or 141 lane-miles) claimed in its 1996 White Paper (Phang and Asher

1997). Is Singapore not going to experience capacity-usurping effect, or what will be

the reasons underlying its policy of capacity expansion?

Here, we might need to look at two things: the optimal investment of roads, and

capacity-usurping effect. The optimal scale of road capacity would be acquired when

long-run marginal cost equals benefit (Mohring and Harwitz 1962; Hau 1992) (Appendix

2). In other words expanding a road until the additional benefit equals the additional

cost of building it would yield maximal net benefit to the community. This might justify

building new roads theoretically. One issue here is the other external costs are not

counted. Another concern is the side effect of capacity expansion, e.g., high lane-mile

elasticity of VMT. Younes (1993) research shows weak capacity-usurping effects were

found in his eight case studies in Britain, Germany and Sweden with relatively new road

building within the past 2-15 years. In these case studies, traffic flow did not increase

significantly enough to remain previous congestion nor did it lead to a significant modal

shift from public to private transport18. He discovered building of new road schemes in

urban area could still be effective and did not necessarily lead to adverse and

worsening conditions, when coupled with appropriate complementary policies (such as

improved public transit, parking control and bypasses). This result is consistent with a

18

This paper does not provide quantitative evidence, such as change of speed.


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case study on the short run impact of a ring road in Amsterdam, Netherlands19 (Kroes,

et. al, 1996). The capacity-usurping effects could still hold in the cases of Younes

study as long as growth continues in these cities in the long run, but the weak capacity-

usurping effects strengthens the support for capacity expansion. The ideas underlying

the differences between the U.S. and the Younes cases could be explained by the

degree of lane-mile elasticity of VMT. In areas (1) with few alternatives of driving (such

as convenient, cheap public transport, pedestrian friendly environment), (2) with auto-

oriented land use (such as low density, unbalanced, separate land use), (3) trend of

growth (e.g., such as cities experiencing the effect of agglomeration, or fast population

and economic growth), and (4) lower cost of driving, the momentum of traffic expansion

to fill the space available to it is stronger. In the American metropolitan areas, where

roads have been overused, and urban sprawl continues due to the failure of

transportation pricing, convenient road network, cheap cars and gasoline, subsidies of

single family housing, and relatively cheap land, new road is obviously not a suitable

plan. If transportation pricing remains implausible, building new roads can not relieve

congestion, but lead to more unbalanced, low-density cities (more unsustainable

environment). In turn, this condition may also lead to further demand for driving (i.e.,

negative spiral). But in those European cities, where induced supply did not induce

significant demand, building new road may be an effective measure to calming

congestion. Younes attributed this success to complementary transportation policies,

efficient public transport and traffic management measure. In sum, capacity expansion

as a means to relieving congestion is generally doubted, only not if implemented in

19

This result from this research may deserve less credit since its survey for the impact of the road opening was


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areas with low lane-mile elasticity of VMT. This conclusion leads to the need for further

research on capacity-usurping effect from counties other than U.S.

Demand Contraction:

Several conditions encourage the use of demand-side measures (e.g.,

transportation demand management (TDM)) to relieve congestion. In many areas, It is

physically impossible to enlarge current road networks, or congestion pricing is

politically or socially infeasible. Besides, English drivers reported that 30% of car

mileage, and 43% in Los Angeles, was not at all or not very important (Kessler and

Schroeer 1995). These situations encourage applying TDM for more efficient use of

current highways20. The fundamental ideas of demand contraction are composed of

reducing total trips made and redistribute trips more evenly or efficiently in terms of

times, modes and routes of travel. This section is divided into non-land-use- (basically

transportation-engineering-oriented) and land-use-oriented for the sake of clarity.

Non-land-use measures: About decreasing travel demand, examples include

encouraging people to work at home, and substituting trips with telecommuting

technology (Kessler and Schroeer 1995), provision of better public transit, and

encouraging ride-sharing (Giuliano 1992). The disadvantages of encouraging working at

home include it can not work for all types of work since a lot of works need face to face

contact. Telecommuting technology as a means to congestion alleviation may be

conducted only two months later.


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criticized for its indirect effect, i.e. stimulating more trips due to more social or economic

interactions.

Next, about redistribution of trips, they will improve the efficient usage of road

network or increase the usage of environment association (on foot, bicycle, public

transit). For example, high-occupancy vehicle (HOV) lane has been in place on many

highways, such as Route 55 in southern Calnifornia(Giuliano 1992), which are

designed to encourage more people to use ride sharing by providing the privilege to

less congested lane (i.e., HOV) (Downs 1992). Many transportation departments also

provide ride-match service for carpooling (Washington 1999). Measures to encouraging

the usage of pubic transit are numerous such as park-and-ride, user-responsive system,

exclusive bus lane, and subsidies. For instance, establishing exclusive bus lane in

Taipei Taiwan, Toronto Canada, and Zurich, Switzerland (FitzRoy and Smith 1993) is to

encourage travelers to use bus by providing better mobility. In Zurich, Switzerland, bus

ridership increased 33 percent from 1985-1990 attributable to exclusive bus lanes and

automatic traffic light signaling that provided absolute priority for public transportation at

intersections. However, car numbers on main roads had been stable from 1981-1990,

which indicated the shift from car to bus seemed marginal. Building the off-road transit

systems, such as people mover, light rail system is good for population dense areas or

cities. Provision of convenient public transit, however, does not necessary lead to shift

from cars to transit. Younes (1995) found the provision of rapid rails of Victoria Line in

London, of S-Bahn and the U-Bahn in West Berlin, Germany only had marginal relief

from road traffic since there was insignificant shift from cars to rail, but substantial shift

20

The approaches to increasing efficiency of existing road usage also include supply-side measures (excluding

building or expanding roads) and pricing.


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from bus to rail. Improvement of parking policy could also help relief congestion.

Shoups case studies of eight firms that have complied with Californias cash-out

requirement, foundthe solo drivers to work fell by 17 percent, and the number of car-

poolers, transit riders, and bikers or walkers increased by 64, 50 and 39 percent,

respectively. Also a before-and-after study within a city district of Munich, Germany

(Topp 1993) shows the effects of residential parking permits on the modal choice of

employee. The share of solo-drivers dropped from 44 to 32 percent, while the share of

environment association rose from 54 to 64 percent.

Without reducing total traveled mileage, diverting traffic into non-congested time

periods and routes are other alternatives for congestion alleviation. In practice, traffic is

not evenly distributed during different periods of a day, or weekdays and weekends, and

on different routes. Several measures could redistribute the demand into alternative

time periods or alternative routes. The measures include staggering working hours

(Downs, 1992),route guidance system, the real-time traffic information of Advanced

Traveler Information Systems (ATIS), by-pass, and road pricing (described in the

economic perspective section below). For example, a research based on simulation

programming suggested real-time en route information could reduce the variance in

travel time considerably in the context of recurrent congestion (Emmerink, et al. 1995).

There are some points requiring notation. Among the measures to redistributing

trips to different times, routes or modes, some researches found mode change was less

likely to occur. The examples include the provision of rapid rail transit in London, U.K.

and West Berlin, Germany (Younes 1995), and the improved mobility of bus system in

Zurich, Switzerland. Besides, the capacity-usurping effect also threatens the result of


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and growth management. These measures are explained in the following.

The major purposes of maintaining density in certain range are threefold, at least.

First, it can support the sustainable public transit, carpooling, biking and walking, and

preventing from low-density urban expansion, which encourage more usage of cars.

These measures include maintaining minimum residential and commercial density,

concentrating jobs in large clusters outside of downtown (for reducing driving to work),

and cluster high-density housing near transit or commute rail stations (for reducing

home-related trips by cars) (Newman and Kenworthy 1991, Downs 1992). In this way,

the demand for road may decreases since more trips are served by public transit or ride

sharing. With regard to mixed land use, it may range from mixed land uses in a

community, mall, block, to in a building. This is another demand-side measure to

alleviating congestion, which functions to reduce trip distance and number of trips since

the origin-destination distance has been reduced and many activities can be conduced

in the same destinations (say, a shopping mall).

Whether these Neotraditional Town Planning components are able to calm

congestion is uncertain. Through the implementation of integration of residential and

commercial locations in neighborhood, higher density land use around bus stations, a

more walking, biking and transit-oriented land use is constructed. The increasing use of

walking, biking and transit is expected to reduce the car usage. (Cervero and Gorham

1995) found transit in some cases of their research ridership was higher in transit-

oriented environment than freeway-oriented. Their research applied a quasi-experiment

on transit oriented and freeway-oriented neighborhoods (micro-environment) in the

same metropolitan area; two metropolitan areas in California were selected: San


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Francisco Bay Area with transit-oriented regional patterns (macro-environment), and

Los Angeles area with freeway-oriented pattern. Six out of seven transit-oriented

neighborhood in San Francisco Bay Area showed higher transit ridership rates than

their freeway-oriented counterparts, but all six pairs in LA did not support this

relationship. This research, however, does not lead to the conclusion that

Neotraditional planning could calm congestion yet. The increased accessibility of

walking and biking (due to shorter distance), and higher transit ridership may divert

some drivers from cars and hence reduce demand of car at the outset. In the long run,

whether the overall trip generation is reduced is ambiguous (Crane 1996). On the one

hand, the increased accessibility (or increased speed) may trigger latent demand (from

triple convergence, higher travel frequency). On the other hand, the reduced cost in the

time and convenience required for trip on foot will both increase the attraction of walking

and other modesthe substitution effectand also increase the amount of time

available for travel by all modes. Even if the overall trip generation is reduced, the

congestion will be reduced or not is still uncertain since space previously used for road

could have been substituted for pedestrian and bicyclists.

Regarding jobs-housing balance, all else being equal, increased supplies of

affordable housing in the vicinity of employment center should fill up largely with

households whose members work nearby, as they would tend to outbid similar

households employed more remotely (Levine, 1998). In this way, the distance of work

trips can be reduced, and the inter-area trips are likely to be reduced. As a result, the

demand for travel will fall, and consequently the traffic demanded will be reduced.

The role of jobs-housing balance to clam congestion is skeptical even the balance


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is achieved, in particular there being many obstacles to its implementation. In 1989

Cervero proposed jobs-housing balance as a strategy for reducing peak-hour traffic

congestion in American cities. Through the reduction of work trip distance and perhaps

switch to walking and biking, internal trips would possibly increase and VMT could

possible reduce initially. One successful case is in Toronto, Canada (Nowlan and

Stewart 1991,Cervero 1996) showed that serious traffic problems were averted in

Torontos central core despite an office building boom in the 1970s and 1980s, through

accelerated downtown housing construction. Levine argued (1998) jobs-housing

balance would contribute little to calming congestion, since the second run of its impact

iteration could come the capacity-usurping effects derived from triple convergence,

increasing trips, travel frequency, or new demand from the new locators. Gordon and

Richardson (1989) further argued that jobs-housing balancing had little effect on non-

work trips (which already accounted three quarters of all trips in U.S. and the majority of

trips during peak hours). In fact, there seems little empirical evidence showing

congestion is less serious in better jobs-housing balanced areas.

Besides, more concerns have been focused on the obstructions to jobs-housing

balance. The success of this measure largely depends on the residential location

selection of the households (demand-side perspective of housing) and the availability of

affordable housing (supply-side perspective). The ideology of residential location

choice-the workers choose homes as close to their jobs as possible(Giuliano 1991)

(given others equal) -is unsupported due to tradeoffs with other goals of the household

(Levine 1998). The logic is that workers still choose homes as close to their jobs as

possible, but have to account for other goals, and to have it balanced with other goals or


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limitations. The variables influencing residential location choice model are numinous:

probably including some trendy ones such as increasing two-worker households,

frequent jobs turnover, affordable housing, exclusionary zoning; other general ones

such as school district consideration, larger house sites, socioeconomic (e.g., same

social class), or environmental (i.e., living near a park); other individual considerations

such as closeness to relatives, living with parents or in inherited housing; or planning

failure such as lacking of phased infrastructure in nearby residential areas, or road

expansion leading to other than nearby areas (Giuliano 1991, 1995, Downs 1992,

Cervero 1996, Levine 1998). Levine (1998) further argued that land use regulation,

even designed for achieving jobs-housing balance, could deter the balance due to

insufficient supply of affordable housing nearby (caused by government or planning

failure). In this regard, market force may work better than land use regulation. In sum,

seeking jobs-housing balance is merely one goal in residential location choice, and

consequently achieving minimal travel cost alone is not consistent with practical

condition.

Different from the above three Neotraditional town-planning elements, growth

management does not eliminate the demand for development and its derived traffic. It

transfers, however, the development to other nearby areas (i.e., imperviousness

principle) (Downs, 1992). Hence, planners should take actions to deal with the

transferred development and the derived traffic. Otherwise, it would just transfer the

congestion problem from one place to another. Besides, since the demand may still

exist, it may bring a negative effect on other people, say middle and low-income

households. For example, the increasing demand for household will increase housing


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prices. Thus, the high-income households could outbid the middle- and low-income

households and they will be then expelled through market force.

The success of land-use measures23 to alleviating congestion is also challenged

by the capacity-usurping effect. Besides, even if the land-use measures could

successfully alleviate congestion, the effects could only be observed long after the

implementation. In general, in highly urbanized areas, the current land use could not be

changed dramatically, in particular in the short tun. This kind of measures take more

time to bear fruits, but once it is implemented, it serves long-term function since

generally land use changes at a relatively slow pace. Hence, it is more like a means to

preventing from future congestion than to solve existing congestion. Inappropriate

current land use plans, on the contrast, could cause future congestion as presented

above.

Congestion Pricing

One primary principle of economists in dealing with problems is to use voluntary market

forces, instead of compulsory administrative regulations. For the purpose of a

distinctive perspective boundary from the transportation-perspective measures, the

economics-perspective congestion alleviation methods, here, are defined as those

means that use price-mechanism of roadway traffic. There are various pricing

associated measures, but in this section the focus is on the congestion pricing due to

23

The credit of land-use measures may exist in improving better accessibility if it succeeds. These measures are

particularly good for population dense countries or areas with limited land supply. This kind of measure may not

work well for people who prefer country-style, low-density, and separate-land-use residence. The worse condition

of these tactics could be in a transit-oriented land use city, the cars are used as primary transportation vehicle, such

as some big, population dense city, without proportional transit systems.


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three reasons. First, its theory would cover the major part of other similar measures;

second, it influences the congested traffic directly; finally it is one of the most promising

measures, in particular capacity-usurping effect has threatened the capacity-expansion

and demand-contraction measures. The other pricing related measures contain pricing

on complements of road usage (such as taxing on gas and plate), and subsides to its

substitutes (such as other transportation modes).

In order to maintain traffic speed at the Pareto efficiency when marginal social cost

equals marginal benefit, price mechanism is applied to internalize social (externality)

caused by congestion (Fisher 1996). This economists theory is derived from the failure

to make drivers bear full costs they generate. In this systemtransportation is taxed

primarily as a consumption good (Institute of Transportation Engineers, 1989). About

the waste of time as the external cost of congestion, it is fair among all road users since

all road users share this cost24 by being slowed down by the congestion. However, it

causes the inefficiency of the whole transportation system. At this point traffic flow is

higher than at the optimal point. This externality justifies the government invention, for

which congestion pricing is probably economists favorite. In addition, jurisdiction of

metropolitan areas is an appropriate to implement congestion pricing (Downs 1992). As

for the calculation of congestion pricing, some transportation economists provide some

theories and formula, such as Decorla-Souza and Kane (1992) (Appendix 3), Borger, et

al (1996).

In terms of the advantages congestion pricing, first, it could be fully applied-at least

technically, if not politically-within a relatively short-time period, say no more than five

24

This external cost of congestion differs from those of air pollution, noise and vibration, which are shared by non-

users too.


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years (Downs 1992). This is because none of the tactics involving changes in

residential or job density or location has that trait. Second, it could be a more

reasonable pricing system with the application of ITS technologies, because it could

charge commuters according to the car size, weight, and the traffic condition. Next, with

this flexibility of floating rates, different levels of congestion can be dealt with at different

congestion prices. Furthermore with the advancing ITS technologies, it could be

applied to all congested road section, no matter highways or local.

About its effects, its initial congestion-reducing effects may not be offset by

capacity-usurping effect. In contrast, congestion pricing can divert the transportation

demand to alternative times, routes, or modes. Also, It may immediately affect all peak-

hour movements on main arterial (Downs, 1992). Furthermore, it affects not just work-

related trips or local trips. Besides, in this system people can make their own choice

about when, which route or which transportation mode to use. Finally, a side benefit is

that it could have income distribution effects if the revenue was used for other nonusers

(Hay 1973). All these advantages explain why academics strongly support congestion

pricing.

Congestion pricing, however, had experienced significant obstructions from

politicians and the generally public, as opposed to the support from academics (Verhoef

and Piet, 1997). Since the emergency of theory of congestion pricing in the 1960s, it

has been in practice in only a few cities around the world. Singapore started its pricing

system since 1970s, and 1995 the system has developed into one area (Area Licensing

Scheme) and one liner (Road Pricing Scheme) congestion pricing (Phang and Asher


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1997). A electronic road pricing (ERC) was scheduled for implementation in early 1998,

which was planned to handle vehicles traveling up to 120 (Km/Hr) when passing

charging points in a multi-lane environment. After a two-year (1983-1985) experiment

with electronic road pricing, Hong Kong dropped out due to the issue about invasion of

privacy (Transportation research Board 1994). In cities of Bergen (1986), Oslo (1990)

and Trondheim (1991), Norway a pricing system was used for raising funds for needed

road improvements, but not based on congestion. The San Francisco Bay Area

proposed to increase the toll for using the San Francisco-Oakland Bay Bridge during the

peak period to shift traffic to off peak and to transit. In Southern California, it was

proposed that solo drivers could pay to use HOV lane on certain highways. Proposals

or researches were brought up for congestion pricing in London and Cambridge,

England. The obstacles to congestion pricing involve the issues of individual loss,

redistributed welfare from road users to the rest of the community, and perverse

incentives for government. In theory(Gomez-Ibanez 1992) stated that three groups of

people would benefit and four groups would lose from congestion pricing. The wining

groups were composed of the (tolled-on) motorists whose gains from improved traffic

speeds outweighed the toll cost, travelers who would use bus or HOV, and government

(Hau 1992), or recipients of toll revenues. The four losing groups consisting of the

tolled-on motorists who had relatively low value on travel time, the tolled-off motorists to

other roads, time or modes, the users of the competing roads or time, and those who

chosed not to travel.

(Hau 1992) attributed the failure of the implementation of congestion in part to

this condition that more people lose from congestion pricing. This condition also brings


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in two inequity issues: first, the poor are tolled off, and the second is the payers (tolled-

on) are not the same as beneficiaries (Evans 1992). To abandon the free access of

roads in favor of access by ability to afford does not allocate to need (Downs 1992), so

congestion pricing may penalize the poor. Hence compensation from the toll revenue is

suggested to pure into improvement of public transit (which can be an alternative to the

tolled-off, in particular the poor). Besides, the traffic it is intended to control primarily

single occupancy car commuters merely transfer the increased cost onto their

companies. From the perspective of the tolled-on, Evans (1992) stated that congestion

pricing was that it might redistribute welfare from road users to the rest of the

community, and introduce horizontal inequality between road users who were subject to

it and those who were not. Consequently, the revenue is suggested to be used to

expand or improve the road system (Evan 1992). The resolutions to these issues

include packaging congestion pricing with other appropriate associated measures

including the use of toll revenue. Some researches showed congestion pricing alone

could gain minor support would gain more major support if accompanied with

improvement on roads or public transit. As for the issue of perverse incentives for

government, Evan (1992) argued that congestion pricing (as a direct charging

mechanism) would give governments the power to exploit monopoly over roads. If this

is true, government may try to raise substantial amount of revenue through overcharge

on congestion pricing and undersupply of roads. The overcharge will distort the function

of congestion pricing (short-term best pricing principle), and undersupply of roads is

against the long-term best investment principle (long term optimal point). In addition,

another difficulty in implementing congestion pricing is the public opposition to paying


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twice for the facility (Fisher 1996). Besides, consumers regard congestion fee as

immediate cost, but the derived benefit such as reduced congestion is intangible or

expansion of transportation can only be achieved in the future. Furthermore, in some

cases government officials are not willing to implement congestion pricing because it

requires interaction with other organizations, which outweighs the costs of delay (Downs

1992).

Congestion pricing may can be better in the society with high demand elasticity.

In the areas with high demand elasticity, the amount of reduced traffic caused by

congestion fee is larger than in the city with low demand elasticity. The areas with low

demand elasticity could be auto-dependent, sparse areas, or in rich society. For

example, in area with better service of transit system, it might need lower congestion

fee to reduce congestion than in auto-dependent areas.

The extent to which congestion pricing changes travelers behaviors in terms of

trip route, time, mode, destination, vehicle occupancy, frequency (Hills 1993),and trip

chaining, as well as location changes is not clear due to limited research. One of the

few cases involves a survey conducted for the morning-peak passengers in the

Randstad area, Netherlands in 1995 (Verhoef, et al, 1997). At that time, road pricing

had just been discussed in the Dutch Parliament again, and a proportion of Dutch users

in the Randstad was expected to be familiar, to some extent, with the concept of road

pricing. The result showed if pricing were in place, the most frequent mentioned

alternative was no alternative at all and trip rescheduling (some 32%). As for

changing residence and changing jobs (location change), using public transit and using

carpooling (behavior change), and canceling trip (some 10 %) were lower than the


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above two alternatives. This, again, strengthens the idea of packaging congestion

pricing with other measures to cope for the diverted demand. As for the congestion

pricing elasticity of demand, few researches have been conducted, but there are some

on the price change in petrol, transit fare (Oum, Tretheway, and Waters 1992;Goodwin

1992).

Interdisciplinary Discussion

A general argument about the implementation of capacity expansion (e.g.,

transportation-engineering-based), demand contraction (including land-use-based) and

congestion pricing (transportation-economics-based) associated measures to cater for

congestion is that one single measure could barely work satisfactorily. Though some

researches suggested certain measures combined could work better than separately,

few academic researches provide affluent theories and evidence on it. On the contrast,

some measures may work better separately than together due to the cancel-out effect.

Theoretically, their push (out of road) effects and pull (to other alternatives) effects, and

their combination cause the reinforced or cancel-out effects of the interaction of different

measures. The following are some discussions on the interactions of capacity

expansion-land use, capacity expansion-pricing, and land use-pricing.

Land use to capacity expansion: road building could be an effective measure

to calming congestion in a balance transportation environment which contains a well-

proportioned mixture of road building and public transport. Road building in U.S.

generally is not considered as an effective one since the vacated space is usually filled


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up rapidly by latent demand, in a system of over-saturated demand for autos (e.g., U.S

metropolitan areas). Younes case studies (1993) showed this condition did not occur

in certain cities in Britain, Germany and Sweden, which was attributed to the balance of

road and transit system. Subsidies to bus, transit-oriented land use, such as higher

density (in particular around transit stations), mixed land use were all components of

these successful transit systems. On the contrary, in the countries with low population-

density and segregated land use such as U.S. and Australia, building new roads as a

solution to congestion is reasonably less expected.

Capacity expansion to land use: To achieve jobs-housing balance a

convenient transportation plan providing access to jobsites and housing is necessary. A

transportation system provides better access to outer areas than the nearby would

explicitly encourage industries and households to move outwards and then increases

imbalance. In a sense limitation on road building could be considered as one kind of

growth management. For one it could press the demand for development or divert the

development to other areas. That is, congestion is used as a tool for managing

development. For another it could divert the development from urban periphery to

existing developed areas. In the former case the existing urban form might remain the

same; in the later case the metropolis might become more compact.

The impact of road building on urban form is possibly quite different from that of

congestion pricing on land use or urban form shown in the following section. Road

building in metropolitan areas could possibly induce development within the affected

area that it serves due to the improved accessibility. This land use changes due to co-

location of firms and households, or influx from neighboring rural (Kilkenny 1998) or


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other areas. In fact road building is a necessary factor for outlying development (i.e.,

urban sprawl) (Gordon and Richardson 1989). Classical location theory indicates the

watershedof the development may spread along the new road if land is available. Law

of constant travel time (Hupkes 1982) argues that work trip time would possibly remain

the same by adjusting travel behavior or locations would help define the possible

watershedof development. The resulting land use changes, however, perform in

different shapes and degree due to natural and artificial factors. The development of

land could be contiguous, or discontinuous to existing urban areas (Weitz and Moore

1998). In terms of their spatial pattern, there are strip, leapfrog, dispersed development

(Ewing 1997). The development could occur in existing area (such as urban growth

boundaries (used in Oregon project) or outside) (Weitz and Moore 1998). Also the

densities of the developments are likely to be different. The prediction of outlying

development caused by capacity expansion is beyond difficulty since many factors are

involved, such as landscape, land value, land use, economic, and social conditions.

From the sake of calming congestion, the U.S. had benefited from road building

but it repaid in other aspects. The urban sprawl relieved the congestion pressure in

urban core, which led to the current, most popular travel pattern-suburbs to suburbs.

The travel time, distance, and speed of work trips remained constant or even improved

partly due to this transition (Gordon, Richardson, and Jun 1991). Nevertheless, there

are various concerns not only from transportation but more significantly from other

perspective. Urban sprawl tends to lead to more auto uses, so congestion might be

temporarily relieved or will be transferred owing to the escape hatch of spatial

redistribution. Eventually, the pressures of growth and deteriorating congestion would


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become overwhelming. High-density development (a common factor of transit-

supportive environment or walking and bicycling) could hardly achieve without strong

planning authorization (Bernick and Cervero 1997) where cheap land is always

available through road building. A crucial reason is the failure of pricing mechanism of

land, which have been constructed of demand and supply of humans, in particular of

this generation. This failure leads to the overuse of land by human beings of this

generation. Also travel distance is likely to increase (compared with more jobs-

housing-balanced land use). Urban sprawl may lead to unbalanced job-housing

balance if job centers and housing are not developed simultaneously. All these possible

impact on land use add to skepticism on net benefit of road building. Particularly

notable, Newman and Kenworthy (1991) found the effect of the provision of

infrastructure for automobiles was more significant than pricing on influencing urban

forms in their research on 32 worlds principle cities.

Congestion pricing to capacity expansion: Probably the most important roles

that congestion pricing plays are first, it can internalize the externality caused by

congestion, and its potential to resist capacity-usurping effects. Capacity-expansion-

and demand-contraction-based measures, on the contrast, are usually criticized for

being unable to serve these two functions. Underpricing tends to lead to overuse of

roads. Without pricing, traffic might turn back to original congestion in urban areas after

the implementation of either demand-contraction- or capacity-expansion-based

measures. These issues justify the significance of congestion pricing to congestion per

se, as well as to the other two groups of measures. Hence, capacity-expansion and

demand-contraction related measures would work better together with congestion


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pricing. For instance, Vuren and Smart's (1990) theory-based paper (1990) concluded

that the combination of electronic route guidance and road-use pricing would create

greater improvement to the transportation system than if each was implemented in

isolation of each other25. However, congestion pricing has been implemented in only a

few cities, and furthermore, few research provides empirical evidence on its practical

effect.

Land use to congestion pricing: Levine (1998) discovered an effect of land

use regulation on road pricing. In suburban areas, land use regulation of the low-

density community tends to push those who are not affordable to live farther away from

the suburban job centers26. They could have lived closer, if there was no maximum

density regulation and the resulting, affordable housing was available. In the meanwhile,

those living in the low-density community are effectively subsidized. Hence, these low-

income employees are double discriminated. He quoted the theory of the second

best27 and then argued that the longer-distance commuter was worthy of a subsidy, not

a tax. What is worse is that congestion pricing makes the unaffordable pay more,

otherwise they have to turn to an alternative, including finding a new job at worse. The

issue he raised here was about the efficiency of road pricing in areas where a principle

desired outcome-relocation to reduce transportation costs- is effectively barred by land

use regulation.

25

Electronic route guidance, as supply-oriented measure, could make more use of available road space;

road-use pricing, a demand-oriented measure, could guarantee all the trips made were socially worthy.

Hence, they could complement each other (Vuren and Smart, 1990). 26

This is the phenomenon that land use regulation causes jobs-housing imbalance (Levine, 1998).

27

The theory of the second best suggests equalizing subsidies for substitutes where societal marginal cost pricing

is not politically achievable (Bailey 1995).


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Congestion pricing to land use: The impact of congestion pricing on land use

or urban form is still a new area lacking empirical evidence because there are very

limited cases of congestion pricing implemented in the world. In theory, congestion

pricing is likely to influence travelers behavior at the outset of the congestion pricing

implementation, and in the long run there are chances that land use or urban form may

change. Congestion pricing may change land use in two ways. The first way is through

a simplified process in the order as follows: change in travel cost, in accessibility of

locations, in value of land, in location decisions, and finally land use patterns. The

second way is through the use of revenue collected from congestion pricing (Elizabeth

1994). In the process of congestion pricing affecting land use, first the increased travel

cost caused by pricing is likely lead to the triple divergence of traffic or reduced activities

(both social and economic). Consequently in the short run traffic flow during peak hours

in congested areas will be reduced to the Pareto point. Besides, the accessibility of

location will change after congestion pricing due to increased out-of-pocket travel cost.

Based on the equilibrium model of urban location that land values are determined

primarily by differential accessibility to the Central Business district (CBD) (Isard 1956),

two popular arguments about the impact of transportation pricing on urban form are

derived. One is priced areas could have higher-density land use patterns and a smaller

metropolitan area (Solow 1994). The other is congestion pricing would have a further

decentralizing effect (to non-priced areas) by reducing the attractiveness of destinations

within the priced areas (Elizabeth 1994). With the relaxation of uniform value of time,

the result will be different. For people with high value of time (e.g., high-income, people

with emergency) may regard the accessibility of priced areas is improved due to the


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savings on travel time. On the other hand, people with relative low value of time (e.g.,

the low income) may regard the priced areas become less accessible and the non-

priced areas is relatively more accessible since where they could trade time (e.g.,

longer travel time) for savings on congestion tolls. Then the class segregation may be

formed if the high-income could move to the priced areas and the low-income to city

center or non-priced areas. As for business location choice, without considering factors

other than market and labor input, the population-serving business may probably follow

the customers (i.e., market) and the labor-intensive industries might follow its labor.

Hence the industrial structure could change in priced and non-priced areas.

Taking other variables into consideration, the condition will be a lot more complex

than the above. Basically, we would like to know the extent to which the change in

accessibility of locations by congestion pricing would influence resident and industry

location decisions, and then the land use. The understanding of the following conditions,

relationships or puzzles may contribute to this prediction job under the circumstances of

few past empirical experience. We would like to know: 1) the response or adjustment

(e.g., changes in travel behavior or new location decision) of residents or industries to

different changes in accessibility caused by congestion toll (which is related to levels of

congestion and demand) and different congestion plans (such as area-wide and arterial

pricing, and with or without accompanying plans); 2) the extent to which different

residents (such as race, income levels) or industries will change locations in the long; 3)

the economic influence on industries caused by the out-of-pocket costs; 4) the area

variables that may encourage or impede moving (such as transportation system, land

value, availability of new places, market conditions, the restrictions of current land use


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code, crime rate, and school district); 5) the influence of use of the revenue gathered

from congestion toll. This theoretical analysis suggests that it is the prediction derived

from the equilibrium model of land value is too simplified since there are lots of variables

left out.

Transportation Research Board (1994) indicated that retail and commercial

establishments in Manhattan in the mid-1980s thought congestion pricing would reduce

the attractiveness of the CBD (Central Business District). Singapore (Phang `993),

however, does not support this argument. Interviews with businessmen and retail

shopkeepers revealed there was no particular influence on sales. Furthermore, labor

availability appears to have improved because of improved public transit. It also

mentioned that congestion pricing would increase jobs-housing balance since workers

would move closer to their work site. Elizabeths (1994) research on San Francisco Bay

Area found firms would response more to area-wide scenario than smaller scale plans

since more of their employee could be influenced. Also low-income employee would

not be affected as much as expected since they generally were more likely to live

nearby. However, this conclusion does not apply to the urban-to-suburban work trips of

the low-income employee. For some firms other factors such as taxes, crime rates, and

the general business climate were more important than transportation in business

location decision. Besides, there were a variety of ways that firms will take in response

to congestion pricing, such as increased parking subsidy, schedule change, and

seeking for exemption from pricing. Furthermore Local government officials were

skeptical about the possibilities for increased development due to higher density since

current land use regulations usually would not allow so. Deakin also stated that if the


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use of the revenue from congestion pricing was in the supply of transportation (e.g.,

building new road), then its impact could be larger than pricing itself.

Conclusion

Through the analysis of the causes of traffic congestion, this paper found there do

exist certain conditions that can make highway congestion unavoidable in urbanized

areas. The increased interaction in human society in terms of economic and social

activities, and the population growth constitute the fundamental power of traffic growth,

in particular as opposed to limited supply of road capacity in urbanized. The supply of

road capacity is getting difficult in the context of sustainable transportation, when the

previously underestimated external cost on environment has been marching into history.

As a result, movement of persons (instead of vehicles) and accessibility (rather than

mobility) become the goals of transportation professionals. Under these circumstances,

congestion turns out to be the tradeoff for the sustainability of society, environment and

economy. Besides, traffics are distributed unevenly in terms of time, space. In this

case for a balanced financial condition, certain time period or day, certain routes need

to be overused to compensate the loss from the underused. The short-turn deficit of

capacity supply is even harder to deal with, such as the decreased road capacity

caused by weather, accidents and routine maintenance. Even if all the above

conditions did not exist, in a transportation system of Pareto efficiency, drivers would

always feel congested during peak hours or days. In an over-saturated system, the


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capacity-usurping effects will bring the congestion back sooner or later after our

endeavor (excluding pricing-oriented measures). This, however, does not mean there is

no need to try to solve traffic congestion. Measures to calming congestion that can

improve the efficiency of road network, as well as achieving sustainable transportation

should still be taken.

Most of measures for alleviating congestion are developed from three main

perspectives: transportation engineering, and economics, and land-use. The scope of

economic measures contains all measures using price mechanism; the land-use related

measures contain measures by changing land-use policy only, considered as one kind

of demand contraction; the transportation measures contain capacity expansion, as well

as demand contraction. For purpose of systematic analysis under demand-supply-

pricing structure, the measures are reorganized into capacity expansion (transportation-

engineer perspective), demand contraction (including land-use- and transportation-

engineering perspectives), and pricing (transportation-economics perspective). Two

common problems that capacity-expansion and demand-contraction measures may

face are capacity-usurping effects and inability of achieving Pareto efficiency. This

condition points out the significance of congestion pricing in alleviating congestion.

However, congestion pricing have not been widely implemented primarily due to political

difficulty. These conditions make it more difficult to dealing congestion. The capacity-

usurping effect was found, however, not very significant in some European cities. This

gap may deserve some researches to fill in.

Through some researches suggested certain measures combined could work

better than separately, few academic researches provide affluent theories and evidence


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on it. On the contrast, some measures may work better separately than together due to

the cancel-out effect. Theoretically, their push (out of road) effects and pull (to other

alternatives) effects, and their combination cause the reinforced or cancel-out effects of

the interaction of different measures. For example, road building is likely to induce

weaker capacity-usurping effects in areas with transit-oriented land use than with auto-

dependent land use. To achieve jobs-housing balance a convenient transportation plan

providing access to jobsites and housing is necessary. On the contrary, capacity-

expansion measures may lead to transit-oriented land use, such as low density, urban

sprawl. The shortage of affordable housing caused by land use regulations may

impede the desired outcome of congestion pricing- relocation to reduce transportation

costs (Levine 1998). Two popular arguments about the impact of transportation pricing

on urban form are: (1) priced areas could have higher-density land use patterns and a

smaller metropolitan area; (2) congestion pricing would have a further decentralizing

effect (to non-priced areas) by reducing the attractiveness of destinations within the

priced areas (Elizabeth 1994). In the scope of interaction among all three kinds of

measures, our understanding are still very limited, not even mentioning that there exist

numerous, variant measures in each of the three categories.


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Appendix 1. Definition of Congestion

D: Demand for travel on highway. S: Supply of highway.

Source: this research

Acceptable

Con estionUnacceptable

Free

Capacity

(Economists)

Acceptable

Con estion

Free

Unacceptable

S

D

Traffic Flow (V)

Cost or time

Forced

Flow

Stable

Flow

Capacity (C)

(Engineers)

Documents

Dealing With Traffic Congestion