Traff Improvement

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Traffic Flow Improvements


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Traffic Flow ImprovementsIntroductionTraffic flow improvem ents represent those actions that can be implemented to enhancethe person-carrying capability of the roadway system, without adding significantly tothe width of the roadway. The range of roadway facility actions available generally fallund er two classifications. Actions primarily oriented to urban freeways or expressways,and the second oriented to arterial and local streets. Most traffic flow improvements areimplemented with a focus on the peak period work trip. However, for many of theseactions such as the improvement of arterial signal systems, their applicability could aseasily be expanded to include traffic conditions throughout the day.The prim ary objective for im prov ing traffic flow is to enhanc e the efficiency of theexisting roadway system and therefore to alleviate traffic congestion and relatedproblems such as air pollution. Other factors motivating their implem entation includefinancial difficulties in supp orting new major transpo rtation projects, and the environmental and physical constraints associated with new infrastructure construction.Moreover, there has been a growing recognition that im plementing program s consistingof several interrelated traffic flow enhancem ent strategies can lead to substantial reductions in travel time and delay.

Definition of MeasuresTraffic flow im provement actions include a range of strategies as summarized in Table 1from the "Toolbox for Alleviating Traffic Congestion" handbook, prepared by theInstitute of Tran sportation Engineers (8). Among the more common actions are thefollowing:Traffic SerializationTraffic signalization represents the most common traffic managem ent technique applied in the United States. It is estimated that of the 240,000 urban signalized intersections in the United States, about 178,000 need equ ipmen t an d /o r timing upgrad ings.Traffic signal improvements generally provide the greatest payoffs for reducing congestion or travel time delay on local and arterial streets. The basic type of improvem entsavailable to improve traffic flow on arterials, include:



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Table 1. List of Representative Traffic Fiow ImprovementStrategies

1. Traffic Sign aliza tion Equipmen t or software upda ting, Timing plan improvem ents, Signal coordination and interconnection, Signal remo val.

2. Traffic OperationsConverting two -way streets to one-way operation,Two-way street left turn restrictions,Continuous median strip for left turn lanes,Channelized roadw ay and intersections,Roadw ay and intersection widenings and reconstruction.

3. Enforcement and Management Enforcement for all of the actions described in this table, Incident Managem ent Systems, Ram p metering.

Reference (8)



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(1) Traffic signal equipment updates- equipment updates would include new, moremo dern ha rdw are tha t would allow for the plan ning of more sophisticated trafficflow strategies.(2) Timing plan improvements- signal timing improvem ents would u pda te the traffic

signal timing to correspond to current traffic flows to reduce unnecessary delays.(3) Signal coordination and interconnection- better interfacing of pre-timed signals ortraffic actuated signals or actively managed timing plans or master controllerswould enhance traffic progression along corridors and minimize the numbe r andfrequency of stops necessary between intersections.(4) Signal removal- signal removal at intersections no longer requiring signalized stopcontrol would reduce vehicle delays and unw arranted stops.Traffic signal control technology, including such applications as computer based controlsystem s, has become very sophisticated. The benefits for imp roving signals is welldocumented and leads to tangible reductions in delay and travel times. In states such asCalifornia that have instituted aggressive programs to improve signal timing, the resultsshow clear and tangible overall system reductions in vehicular delays, stops and traveltimes.Traffic engineers also can use signals to enhance pedestrian mobility and safety, sometimes at the cost of restricting vehicular travel. In cities such as Boston, Oakland andNew York where residential neighborhoods abut heavily used and congested highways,selected traffic signals have been p urposely n ot coordinated to increase delay and traveltimes so as to discourage comm uters from using local residential streets to bypass thecongestion of the abutting highway. Analogously, traffic engineers can use a "carrot andstick" approach by coordinating signals along certain desirable streets and rou te alignments to attract or confine traffic to these corridors. Moreover, many municipalitieslack an ad equate staff of professionals that are able to plan, maintain and u pda te thesignal systems in place.

Traffic Operations

Traffic Operations consists of several types of roadw ay improvement projects.(1) Converting two-way streets to one-way operation improves corridor travel timesand increases roadway capacity by eliminating opposing left turn lanes andprovid ing for better signal coordination. Particularly in man y downtow n areaswhere the width of roadway s may b e inadequate for two-way traffic plus parkingand goods delivery, converting to one-way operation and especially in conjunctionwith o ther streets to dev elop a grid circulation patte rn can be very beneficial interms of improving the overall effectiveness of the system.



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(2) Two-way street left turn restrictions is a means of eliminating conflicts with leftturn movements, thereby reduce congestion and delay for peak periods or forthroughout the day. At selected locations where heavy volumes of traffic providefew gaps for left turning movements, the restriction can dramatically reducequeuing and improve the overall capacity of the intersection by as much as 25 to 30percent.

(3) Continuous median strip turn lanes separate turning vehicles from through trafficby providing a "storage" lane separate from the movement of through vehicles.Where the roadway width permits, the median lane layout can provide overallcapacity (and safety) improvements for an arterial corridor that are similar in scaleto turning restrictions at an intersection.(4) Channelized roadway and intersections improves vehicular flow and capacity byclearly marking with striping and signage travel lanes and paths to reduce motoristconfusion and uncertainty by channeling traffic in the proper position of the street.They also serve as a "barrier" for opposing streams of traffic.(5) Roadway and intersection widenings and reconstruction may reduce bottlenecksalong sections where traffic capacity is below that of the adjacent street. Roadwayand intersection widenings and reconstruction represents a host of traffic flowdevices such as improved design, traffic islands, turning lanes and signage toimprove the flow of vehicles and the safety of pedestrians. These measures amongother benefits help to reduce the number of conflict points among vehicles and helpto control the relative speed of vehicles both entering and leaving an intersection.In the Boston Back Bay transportation study, three major intersections that currently exhibit serious congestion were rebuilt based on a new design whicheliminated the congestion and improved the level of service of the intersection to

conditions considered good (3).Typically these roadway changes require only signing and pavement marking changesinvolving little new construction, and therefore are relatively inexpensive and quick toimplement. The feasibility and cost of widening a roadway or intersection is largelydependent on whether additional right of way is required. Their implementation isusually based on alleviating a specific traffic problem in a relatively small or local area,and usually to reduce congestion or a bottleneck at one or several specific intersections.

Enforcement and ManagementEnforcement and Management consists of several types of programs.(1) Enforcement for all traffic flow improvements is required to achieve success.Enforcement of traffic and parking program regulations is necessary when individuals are required to change or adhere to a particular travel and parking behavior.



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(2) Incident Management Systems may consist of one or some combination of rovingtow or service vehicles, motorist aid call boxes, incident teams, detectors in theroadway lanes to monitor traffic volumes, signage systems, traffic operationscenters, contingency planning, and improved information availability to consumersthrough radio and television stations.1(3) Ramp metering is a proven technique to improve traffic flow on freeways. Using amodified traffic signal placed at the end of a ramp, metering allows traffic to enterthe highway either at pre-timed intervals or at times determined by traffic volumeson the ramp or on the highway. Although additional delays are incurred by theramp traffic, mainline roadway capacities are protected and the overall travel timeor speed is improved.Because enforcement costs may be substantial, the program is typically earmarked forprojects potentially having a major impact on area-wide mobility. For example, aperiodic program of enforcement along an HOV lane facility or on a major arterial in thedowntown core to eliminate vehicle blockages in intersections or to eliminate doubleparking.Highway incident management systems respond to congestion that is recurring (i.e., dueto capacity, breakdowns, or operational problems) as well as non-recurring or incidentin nature. Recent studies have indicated that on urban freeways, non-recurring congestion may represent about 60 percent of all freeway congestion. A 1986 FederalHighway Administration study indicated that such a system could substantially reducecongestion on approximately 30 percent of the major urban area mileage (5).Ramp metering typically requires a considerable amount of time to plan and implement.Of particular concern are potential queues that can form on arterials that feed the rampsand generate severe congestion as a consequence of the action. Motorists may choose toby-pass those ramps where metering has been installed to avoid delays. If enoughpeople do so, this diversion could result in the creation of congestion on arterials thatmay not otherwise have a problem.As this list suggests, there is a considerable range of actions that are available to improve traffic flow. However, equally apparent is the breadth of their applicability, andthe potential that many of these actions could have associated impacts that reduce orobscure their affects on improving air quality. Traffic flow improvement programstypically have been implemented and monitored by traffic planners and engineers,thereby giving emphasis to the potential of these actions to reduce traffic congestion andvehicle delay. While these results would generally have a beneficial affect on reducedvehicular pollutant emissions as well, substantive surveys that focus exclusively on theaffects of these measures on air quality have been limited.

1/ Incident management is particularly important when traffic is being maintained during thereconstruction of a major roadway. The topic of traffic maintenance during construction isdiscussed as part of the chapter on Special Events.



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ExamplesSacramento Signal System Improvement ProgramOver the past several years, the City of Sacramento has initiated a series of systematicprograms to improve its signalized traffic control systems. The programs hav e includedchan ging s ignals that are primarily located in outly ing areas from a syste m of interconnected, p re-timed sign als to a system consisting of traffic-actuated signals op eratedby com puter based control. To impr ove the 220 fixed-time signal intersections locatedmainly within the Downtown area, the City received direct financial and technical assistan ce throu gh the California Fu el Efficient Traffic Signal M anagem ent (FETSIM)program to re-time and optimize the signal phasing to minimize delay and increaseoverall arterial travel s peed s. A later program is env ision ed b y the City to install amaster computer network that will a llow the traffic system to be more thoroughly monitored and controlled from a central site.The programs were developed and implemented by the City's Department of PublicWorks and were viewed by the Department primarily as congestion relief measures toincrease roadw ay capacity and travel speed s. On some Do wn tow n streets such as 12thand 16th, the green time is lengthened considerably during peak periods to promotethese roadw ays as commuter arterials and primary Dow ntow n access links to the surrounding regional highway system.Subsequent surveys iden tified several po sitive results. The arterials located in areasoutside the Downtown all experienced reductions in vehicle delay averaging about 5percent (as measured in veh icle hours of travel). Particularly positive is that the benefitsare deriv ed thro ugh out the day and not just at peak travel period s. For signa lizedroadways within the Downtown, the data indicated that the signal timing optimizationprogram has lead to an overall travel speed improvement of 10 percent with a comparable improvem ent in vehicle delay. Vehicle counts for 12th and 16th streets showthat the "preferential signal timing" strategy has likely caused traffic to increase on theseroadw ays, along with a higher travel speed during the peak periods. No t determinedconclusively was whether this induced demand represent trips diverted from otherstreets or if the additional vehicles represent new trips.

Back Bay (Boston) Traffic Operations and Managem ent StudyIn the Fall of 1987, the City of Boston Transportation Department initiated a compreh ensive stud y of the City's historic Back Bay district to dev elop a short and lon grange transportation m anagem ent policy p lan. The Back Bay is hom e to 16,000residents. It is also a center of emp loymen t w ith almost 50,000 workers, nearly 6,000hotel rooms, several major retail centers, and a number of cultural and educationalinstitutions . This diversity is an important strength. Ho we ver, the great amoun t ofactivity that is generated in the area also leads to tremendous competition and congestio n with in the lim ited am ount of street space available in the area. One of the



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study 's key objectives to im prove traffic circulation reflects this conflict b y specifyingthat while access to the comm ercial area needs to be enhanced , traffic intrusion in theabutting residential areas mu st be reduced.The study identified and ana lyzed a large number of alternative circulation o ptions.One alternative that wa s advanc ed by residents impacted by com muter or non-localtraffic w as to create an "island" affect to the residen tial area. This w ou ld inv olv ediscouraging traffic through such measures as reversing the direction of streets on ablock by block basis and modifying traffic signal timings to eliminate coordination andsignal progression be twee n intersections, i.e., to dramatically increase travel time anddelay for a large Dow ntown area of the City.The traffic circulation option that was eventually recommended and implementedachieved the same objective, but through a series of more positive operational andenforcement measures that encouraged d esirable travel, rather than discouraging tripmaking in the area, and also reducing overall travel time and delay in the Back Bay. Theplan involved implementing a combination of traffic operational, management andenforcement measures for those arterials that were identified as high priority commuteror through-trip travel routes into and within the area.The traffic plan primarily focused on tw o major arterials in the Back Bay, MassachusettsAvenue which runs north and south and Boylston which runs east and west. The trafficoperational measures implemented included: Left-turn restrictions at several intersections that currently experience a poor levelof service; Left turn bays at several other locations to reduce conflicts; and Street wid enin gs (sidewa lk cuts) of a few feet at several sections to gain an additional travel lane or allow for a left turn lane.Management measures that were implemented involved on-street parking and includedestablishing new no-stopping zones at selective locations either for the peak period orthroughout the day, relocation and consolidation of cab stands, tour bus stops, loadingzones and handicapped parking spaces, and removal of short-term parking meters.(Video and tim e lapse surveys indicated that many m etered spaces were occupied long-term by area residents, emp loyee s and even b y hotel parking valets w ho w ere illegallyfeeding the meters throughout the day.) Enforcement activities featured a highly visibleprogram that included meter maids, motorcycle police officers and tow trucks.The plan wa s a reflection of City policy that the primary function of a major arterial isthe movem ent of traffic du ring periods of heavy travel. The benefits derived from thetraffic plan on area mo bility wer e significant. Illegal long -term parking at on-streetmeters wa s reduced considerably. Double parking wa s almost eliminated. Averagetravel spee ds on the arterials increased from as low as 6 mph to over 12 mph (Figure 1).

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This resulted in travel time reductions of over 30 percent for both roadwa ys. Significantly, arterial travel times after implementation remained relatively constantthroughout the day rather man deteriorate significantly by the afternoon peak period aswa s the case before the plan was implem ented. These travel time reductions w ererealized despite traffic counts that indicated mat the arterials were carrying 30 to 40percent more traffic du ring the peak hours. An alogo usly, traffic cou nts indicated thatother roadways, and particularly several streets located in residential areas, hadexperienced a correspond ing reduction in veh icle use, ranging from 5 percent to morethan 40 percent of the peak hour traffic. This substantiated computer traffic forecastswhic h h ad been run for each traffic optio n, and which indicated that significant improvem ents to the tw o key arterials would cause traffic to shift from the slower, minorarterials and local streets of the Back Bay. The computer analysis further indicated thatwh ile the traffic plan wo uld no t reduce total vehicle mile s of travel (VMT) in the BackBay, it w ould reduce daily veh icle hours of travel (relative to a do-nothing option) by anestimated 5 perce nt

Chicago's Incident Management ProgramChicago's incident management program started in 1960 with a crisis on the newlyope ned K ennedy Expressway (2). Design ed to handle 1,500 vehicles per hour per lane,the new h ighw ay w as quickly swam ped as peak-hour traffic vo lume s exceeded 1,000veh icles per hour per lane. To manage the crisis, the Illinois Departmen t of Transportation (then the Department of Public Works and Buildings) assigned twenty peop lein pick-up trucks to the job of patrolling the expressw ay d uring the morning and afternoon peak commuter periods. The emergency patrol, eventually named the "Minuteman Patrol," was charged with keeping the Kennedy Expressway open by clearingtravel lanes of disabled vehicles. Today the program em ploys sixty peop le, covers 80miles of the 150-mile expressway system, and operates twenty-four hours a day. It hasan annual operating bud get of $3.5 million funded from state motor fuel taxes.The Minuteman Patrol program has survived and grown because the highly visiblepresence of the service patrol and their focus on personal service has built strongsupport and a positive reputation for the Minutemen. But maintaining the program hasbeen a struggle.Illinois DOT has never had a formal mandate for the Chicago program. Illinois DOT hasa single high wa y district that covers the Chicago metropolitan area, but the incidentmanagem ent program is a com posite of three divisions w ithin the district. The IncidentManagem ent Office and the M inuteman Patrol are under the jurisdiction of the IllinoisDOT Bureau of Traffic; the communications center under the Bureau of ElectricalOp erations; and the Transportation Sy stems Center under its ow n Bureau of Transportation Systems.

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Figure 1. Boston Back Bay Transportation Study, Effects of TrafficOperations and Management Improvements to Boylston Street

Parking Conditions o n Boylston Street100 :

80 - 1 iS 1 Before Enforcement90 ' S 3 After Enforcement'0 - KS60 M^| 50 40 - B^ R30 - Ks0 JH^0 < |Long-term Double Total VehiclesParkins Parking Parked on Street(6 +hours)

Type of Parking Activity

Average Travel Speed s on Bo ylston Street

Speed (mph)1 4 - . J .12 - - After Enforcement

Before Enforcement10 8 6

8 A M 10 AM 12 noon 3 PM 5 P MTime of Day

Source: (3)Traffic Flow Improvements


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In 1988, the Minutemen respon ded to about 100,000 incidents. Of these 60,000 involve ddisabled vehicles; 30,000 were for abandoned vehicles , debris on the road, and fires; andthe remaining 10,000 wer e accidents. Programs managers estimate that most incidents,even small breakdowns, are detected within twenty m inutes, and clearance times formajor incidents hav e been redu ced from four and six hou rs to about tw o hours. Acritical factor in this is the high level of experience among the M inuteman personnel.The Minuteman program returns about $17 in benefits for each $1 invested in theprogram. The total program costs $5.5 million per year. The program save s motoristsan estimated 9.5 m illion vehicle-hours of de lay at a value of $95 million per year.Illinois DOT removes autom obiles and trucks from the exp ressways as fast as possible.They will do so even if there is a risk that they will further damage the vehicle or itscargo. Illinois DOT generally d oes n ot allow motor carriers the right of first refusal tohire their own tow ing contractors or to hand pick a load before rem oving a trailer fromthe expressw ay, espec ially during peak periods. Initial concerns about incurring substantial liabilities under the fast removal po licy have not materialized. Autom obileowne rs and motor carriers may claim dam ages from the state, but very few do so . Thestate police will authorize private tow companies to remove vehicles from the expressway s in non-emergency situations; and all vehicles towed by the Minutemen areturned over to private contractors at safe drop sites near the expressways.Illinois DOT's traffic information services ma y have as much impact on r educingincident congestion as the patrol and clearance programs. During peak periods, DOT'sTraffic Systems Center provid es Chicago's commercial radio and television stations withtraffic and incident information every five m inutes.Chicago has established an effective incident management program, but it does not havea coordinated regional program. Chicago has no formal mechanism to bring togetherthe managers of the different agencies invo lved in incident managem ent. Interagencyrelationships depe nd on personal relationships built over the years. Observers inChicago believe that the next major challenge for Chicago is to develop an integratedregional incident management program.

New York/New Jersey Transportation Operations Coordination Committee(TRANSCOM)TRANSCOM, the Transportation Operations Coord inating Com mittee, is a publicprogram funded and staffed by its fourteen member agencies, which include the PortAuthority of New York and New Jersey, the New York State Department of Transportation, the New Jersey Department of Transportation, and the New York City Department of Transportation (2).TRANSCOM has fashioned a regional incident management capability for the NewYo rk/ Ne w Jersey metropolitan area by acting as a value-added provider of information.

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TRANSCOM gathers and disseminates information about incidents and traffic conditions. Its clients are ninety-six transportation and traffic enforcement agencies in themetropolitan area. TRANSCOM's services have resulted in improved traffic coordination across the region and a forum for corridor and regional incident planning.When an incident occurs, TRANSCOM's traffic information center collates informationabout the incident, assesses its potential traffic impact, and notifies agencies that mightbe affected. The information is sent directly to agen cies and traffic reporting servicesusing alphanumeric pagers, telephone, and facsimile machines.For the participating agencies, TRANSCOM's service saves time. Operations managersmake only one call, rather than ten or twenty, t o ensure that notification procedures areset in mo tion . Notification is immed iate; there is a record of the transaction; and thepotential for embarrassing oversights is minimized.Timely information about incidents and traffic conditions is valuable because the regional highw ay network is saturated, and even moderately severe incidents can triggersubstantial congestion . It is also valuable because the region must mob ilize manyagencies to respond to an incident. The New Yo rk /Ne w Jersey region is blanketed withmultiple jurisdictions. Within the 500 square miles of the metropolitan area served byTRANSCOM, there are 3 states, 23 counties, over 300 municipalities, and nearly 20independ ent authorities. Many of these jurisdictions have several agencies involved intransportation and incident management.The prospect of gridlock caused by construction projects intended to solve congestionproblems - led to the formation of TRANSCOM in 1985. TRANSCOM's initial mandatewa s to maintain regional traffic capacity. It wa s to do this by improv ing comm unications among its member agencies about planned improvement projects and coordinating the timing of these projects to assure that parallel routes were not under construction at the same time.Today, TRANSCOM maintains a comprehensive data base on its member agencies'construction projects. TRANSCOM dissem inates a week ly traffic advisory report onregional projects that may have interagency impacts. The advisory report goe s out byfacsimile every Thursday night so that it is available to the agencies on Friday morningas they prepare for the next w eek's construction activities. TRANSCOM has recentlyadded information about the completion of projects so that agencies know wh en trafficrestrictions are lifted.

TRANSCOM's traff ic information center operates twenty-four hours a day.TRANSCOM's budget has grown to $1.7 million per year and is now supported by adozen agencies.The growth of the program has m ade it possible for TRANSCOM to expand its role as abroker for corridor and regional contingency planning. The TRANSCOM meetings arethe sole forum where New York and N ew Jersey officials involved in traffic and incidentmanagement can meet their counterparts in other agencies and conduct business.

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TRANSCOM and the agencies ha ve us ed this as an opportu nity to create corridor leveltraffic management teams and define formal contingency plans.TRANSCOM is look ing to new services to broaden its constituency and funding base. Itis currently work ing w ith its agencies to coordinate the use of changeable m essage signsacross the region. TRANSCOM is also trying to target information to specific markets.Under an ATA Foundation demonstration grant, TRANSCOM is p roviding incident andconstruction advisories directly to twelve motor carriers that operate in the NewYor k/N ew Jersey region.

Transportation and Air Quality ImpactsTraffic SignalizationTraffic Sign alizatio n generally provides the best and most available tool available toreduce congestion on local and arterial streets, although the effects on vehicular emissions can be difficult to quantify.Actions involving traffic signals focus primarily on improving the efficiency of theroadw ay system by reducing delays and stops. Therefore, they would improve airquality by providing for higher travel speeds wh ich lower emissio ns. The informationshown in Table 2 from the Federal Highway Administration illustrates the significanttravel speed and time benefits available through several types of signal systemimpro vemen ts. Especially impressive are the travel time and vehicle delay improvements that are available through such straight-forward programs to optimize thetimings of existing sign als or to coordinate signals to provide for signal progression.The data indicate that travel time improvements from 10 percent to 25 percent arepos sible. Of course, actual results will vary by roadw ay segm ent according to theamount of traffic that regularly uses a particular facility and to the extent that thecurrent signal system m ight already have undergone some form of upgrading.An important consideration to improving signals is the possibility for inducing additional traffic or increasing the vehicle miles of travel (VMT). As illustrated in theBoston Back Bay study, signal (and other traffic operation) improvements can attractadditiona l veh icles by reducin g travel times on affected corridors. In the Boston casestudy, the additional peak period traffic was diverted from nearby and less sociallyacceptable routes. This lead to an overall increase in travel speeds, although VMTremained un changed . How ever, the more fundamental concern in other areas is thatmotorists might be diverted from alternative mod es of transportation, or at a minimum ,the signal imp rovem ents m ight induce m ore and longer trips during peak and off-peaktravel periods. The subsequent increase in VMT along a roadw ay w ith improved trafficflow w ou ld at least partially offset any short term air quality impro vemen ts generatedby faster, more consistent travel speeds.



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Table 2. Traffic Signal Improvements

Improvement inBefore Condition After C ondition Speed or TimeNon -Interconnected, Pre-Timed Signal Com puter Based Control 25%With Old Timing PlanInterconnected; Pre-Timed Signal Computer Based Control 18%With Old Timing PlanNon-Interconnected Signals Computer Based Control 16%With Traffic-ActuationInterconnected Pre-Timed Signals Computer Based Control 8%With Actively Managed TimingInterconnected Pre-Timed Signals Optimization of Signal 12 %Various Typ es of Master Control and Timing PlansTiming Plans

Reference: (4)



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Because signal impr ovem ents d o reduce travel times and stop and go driving conditions, they also will produce measurable reductions in carbon mon oxide (CO) andhydrocarbon (HC) emission s. Altho ugh system or region wi de air quality benefits arelikely to be low, their measurable local benefits to air quality and congestion reliefwithin dow ntow n and other major activity areas warrants their continued implementation.Traffic OperationsTraffic Opera tions are similar to signalization improvem ents in that they primarily areoriented to reducing congestion on local and arterial streets by improving the efficiencyof the syst em . Their benefits to air quality are easier to define at the local level thansystem-wide.All traffic operation actions focus on improving the efficiency of-the roadway system byreducing d elays and sto ps, and improv e air quality by allowing higher travel speedswh ich lowe r emissions. Du e to the specific nature and variability in app lying each ofthese imp rove me nts, consistent data that evaluate all their benefits are minim al, although the results of particular projects are available.Generally, each action will improve traffic flow and safety. In Boston, reconstruction ofseveral intersections imp roved level of service considerably. In San Francisco, datacom piled for turning restrictions imp osed for a series of intersections indicated thataccidents were red uced by 40 to 50 percent. In Wichita Kansas, implementation of leftturn bays and lanes reduced accidents ranging from 40 to nearly 70 percent and improved intersection capacity from 12 to 20 percent.These actions are very specific in their nature and usua lly applied in d ow ntow n andother major activity centers. The Boston Back Bay case stud y provides an assessment ofhow assembling several of these actions along with signalization improvements andenforcement can provide a powerful traffic operations plan that can fundamentallyaffect circulation in a relatively large area and result in overall improvem ents in systemtravel speed and efficiency.Traffic operation measures are similar to traffic signal improvements as they essentiallyrelieve congestion and stop and go driving. Their system or region wid e benefits to airquality are probably low. Ho we ver, in conjunction with their proven effectiveness toimprove traffic bottlenecks and flow, they likely provide measurable reductions inlocalized carbon monoxide (CO) and hydrocarbons (HC) emissions.



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Enforcement and ManagementEnforcement andManagement programs provide a variety of tools that standing aloneor in combination with other measures such as traffic operations and signalization improvements can provide an additional means to improve traffic flow conditions bothlocally or at the corridor w ide level.EnforcementThe most effective deterrent to traffic violations is consistent enforcement (usually bypolice highway patrols) to reinforce the need to comply with p roper usage of lanes. Areview of before and after case studies involving HOV lane violations clearly indicated arelationsh ip between the level of consistent enforcement and violations. Where regularenforcement of HOV lanes has always been maintained, such as for the North Freewayin Houston and the Shirley Highway in Northern Virginia, violation rates of under 5percent of total vehicles using the HOV lanes were cited. Where jurisdictional, legal orfinancial impediments restricted HOV lane enforcement, such as the Southeast Expressw ay in Boston and 1-95 in Miami, violation rates of over 40 percent were observedand the travel time benefits reduced considerably from earlier experiences.Enforcement of traffic and parking programs to improve local and arterial streetmobility also can be critical to the overall success of a traffic managem ent program asshown in Figure 1 for the Back Bay project in Boston. In this example, the application ofintense enforcement of parking regulations along a critical arterial roadway resulted inincreasing cu rb-side park ing capacity by reducing the num ber of illegal long-termparking at metered spaces, which resulted in a dramatic reduction in double parkingand increasing the arterial capacity enough to reduce travel times by 30 percent, anddespite the additional traffic attracted to the arterial by the improvem ents.Incident Management SystemsMany levels of sophistication are possible. Though the use of such systems, however,incident duration can be reduced by an average of 10 minutes. A 1986 Federal HighwayAdministration study revealed that such a system could reduce congestion on approximately 30 percent of the major urban area highway mileage.Data related to incident-caused congestion is sketchy, although examples do exist. TheLos Angeles 42 mile freeway electronic surveillance project produced reductions indelay of 65 percent, and other systems have reported approximately a 50 percent reduction. At another Los Angeles location where incidents are monitored with pavement detectors and closed circuit television cam eras, incident managem ent teams aredispatched to clear major incidents. The average dura tion of lane blockages dur ingincidents has been reduced from 42 minutes to 21 minutes.The ITE "Toolbox for Alleviating Traffic Congestion" handbook states that 60 percent ofall freeway congestion may be caused by non -recurring events such as accidents andbreakdowns. The handbook further states mat during periods of congestion, an incidentmanagement system could decrease travel times by 10 to 45 percent, i.e., for all sectionsof a highway that are currently congested, approximately 60 percent of these sectionsTraffic Flow Improvements 15


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could be upgrad ed to relatively free-flow conditions through use of a surveillance andmanagement system.Ramp MeteringMany cities regularly use ram p metering to manage traffic congestion. A survey mad efor the Federal Highway Administration showed that travel speeds on the highwaywere increased by nearly 30 percent after installing ramp metering. Even wh en delayson ramps were in clude d, the average sp eeds still increased by 20 percent and traveltimes decreased by 17 percent. Different levels of control have been implemented, frommetering to improve one or two specific problem areas to attempting system-wide applications such as in California whe re Caltrans is developing a Traffic Operations System concept for the Bay Area that would include ramp metering on m ost of the highwa ycorridors.Benefits to air quality wo uld obviously be greater with larger-scale metering programs,although there could be increases in localized CO concentrations in the areas ofindividua l ramps if exces sive queu es develop . In add ition, it is important to take intoaccount the excess em issions that may occur during high leve ls of ramp acceleration inevalua ting the air quality benefits of ram p metering. As cited in the ITE 'Toolbox forAlleviating Traffic Congestion" handbook, broad application of ramp metering hasresulted in significant benefits to regional mobility. The Minnesota Department ofTransportation compared conditions on a highway before and after a metering systemwa s installed and found that peak hour speeds increased from 37 to 43 mp h. Otherlocations were cited as experiencing speed increases of 30 percent, wh ile reducing congestion by approximately 60 percent.Ramp metering is an effective meth od for improving the efficiency of a highway system.How ever, many of the case studies indicated that along with travel speed improvem entsbrought about by the ramp metering were measurable increases in traffic volumes,which raises the possibility that metering may induce additional traffic or increasevehicle miles of travel (VMT). Several studies have concluded that this additional trafficwas primarily attracted from other roadways. However, no detailed surveys have beenconducted to determine whether the additional traffic also includes shifts from othermo des. Where large-scale metering is implem ented and resulted in substantial improvem ents to travel speed, it is likely that some percentage of any additional traffic orVMT detecte d wo uld reflect a shift from another mode of travel. This wo uld at leastpartially offset an y air quality improvements generated by faster, more consistent travelspeeds on the highway system.

Program CostsThe cost to implement traffic flow improvements ranges considerably as summarized inTable 3. Strategies involving right-of-way acquisition or construction have relatively

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Table 3. Representative Traffic Fiow Strategy Costs

Cap ital CostsTraffic Signalization

Equipment or software updating $2,000-$10,000/SignalTiming plan imp rovem ents $300-$400/Signal*Signal coordination and interconnection $5,000-$13,000/SignaISignal rem oval $300-$400/Signal*Traffic Operations

Converting two-w ay streets to one-way $500-$2,000/BlockTwo-way street left turn restrictions $400/IntersectionContinuous median strip for left turn lanes $2,000/BlockChannelized roadw ay and intersections $200-$500/Block or Inters.Roadway and intersection reconstruction Widely varyingEnforcement and M anagement

Enforcement for HOV Lane Facility $70,000-$100,000/Yeai*Enforcement for Do wntow n M anagement Plan $500,000-$l,000,000/YearIncident Management Systems $1,000,000/MileRamp metering $50,000/Ramp

Operating, Maintenance or Labor Cost Only



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striping, markings and signage would cost about $200 to $500 for each block or intersection. Roadw ay and intersection reconstruction can be very expensive in urban ordowntown areas if additional right-of-way is required or construction involves manyutility relocations.Systemwide traffic operation improvements that involve many sites can result insignificant costs to implement. The Back Bay Transportation Study in Boston developeda program of non-signal traffic improvements that included dozens of intersections,with actions that included peak period turning restrictions on the area's major arterials,street reversals, parking restrictions, left turn bays, new channelization layouts andreconstruction of several major intersections to improve circulation and safety. Most ofthese actions were inexpensive, with reconstruction of intersections, at $100,000 to$200,000 per location, clearly reflecting the highest cost of these actions. The total cost ofthis program was estimated at over $6,000,000.

Enforcement and ManagementEnforcement and Management reflect actions that include equipment and capital costs,or operating and maintenance costs. A facility enforcement program includes the laborcosts associated with traffic control officers providing patrols and surveillance of thefacility d ur ing its opera tion . A cost of $70,000 to $100,000 to enforce one HOV lanefacility pe r year reflects the level of enforcement in p lace in such areas as Houston andNor thern Virginia where HOV lane violation rates are below 5 percent. A traffic andparking enforcement program that includes meter maids, uniformed police officers andtow trucks to cover several major and minor arterials within a downtown can cost from$0.5 to over $1.0 million per year. However, the revenue generated by the fines issuedas part of an enforcement program generally exceed costs by a factor of at least seven oreight.An incident management system that consists of such sophisticated elements as embedded traffic detectors, changeable message signs, closed circuit television and sometype of central com puter control will cost about $1,000,000 per mile to implement. Thisestimate is largely based on the electronic surveillance project that was implemented inLos Angeles. The Minuteman program in the Chicago Metropolitan area is reported tocost $5.5 million per year but saves motorists an estimated 9.5 million vehicle-hours ofdelay at a value of $95 million per year. Ramp metering costs about $50,000 per ramp; ahighway corridor system ramp metering would cost over $1,000,000.

Implementation ConsiderationsThis discussion of traffic flow improvement strategies has focused primarily on potentialtransportation and air quality related benefits that such actions would provide.



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However, despite their positive impact for improving the effectiveness of a transportation system, a num ber of institutional issues can obstruct the implementation of mostof these actions. For any improvement to be successful, good coordination needs to existbetween state and local traffic agencies and with the police department having enforcement responsibilities.Traffic Signalization and Traffic Operation improvements typically are implementedby dt y and county public works departments, with finanda l assistance usually providedfrom State and Federal funding sources. Since these actions fadlitate urban driving,they usually generate little public opposition, with the exception that project abuttersmay object to the disruptio n caused by construction a nd to such actions as street reversals. Impo rtant factors, therefore, that should be considered to minimize potentialobjections and facilitate implementation include the following: Many small jurisdictions and even some large central cities hav e limited trafficengineering capabilities and budg ets. In these cases, traffic signal managem ent androadway maintenance and design is often limited to the most basic or rudimentaryinstallation and maintenance functions. State Departments of Transportation have a strong influence over the allocation offederal roadway aid funds. Many states have priorities that stress high-capital roadand b ridge building, and that do not include traffic operations and signal controlsystems. Traffic operation improvem ents require a public plann ing process to generate localsupp ort for the actions. The potential impacts of each strategy must be identifiedand clearly communicated. The potential benefits and costs mu st be clearly articulated. For exam ple, for a proposed turn ing restriction, the am ount of traffic to be

diverted and the potential alternative travel paths to be taken must be consideredand reviewed with the public. For the planned reconstruction of an intersection,construction schedules must be developed and reviewed by those who will be directly impacted by the project to reduce their concerns and possible opposition.Enforcement and Management strategies typically involve a substantial amount of timeand pla nnin g to imp lem ent. Following are several key factors that need to be considered for enforcement programs: Enforcement is probably the most important factor necessary to ensure success for allthe other actions considered in this chapter. Heavy enforcement must be part of the early stages of a project to reinforce the needfor changes in attitude and behavior. Given this effort early-on, the level of enforcement can be reduced later. The design of a project shou ld provide for self-enforcement. For an HOV lane, forexample, physical barriers clearly prevent casual violations.



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A successful enforcement program includ es a suitably structured system of fines thatserve as a deterrent in itself. Relatively low fines d o little to support other elementsof an enforcement program. An alogou sly, very high fines may not be consideredacceptable by the majority of users and foster public resentment of the program.Implementation of Highway Information Management Systems and Ramp Meteringmay take a number of years. The typical schedule from conceptual planning to a completed system may require 5 to 10 years.The planning phase for such systems must include participation from local officials andfoster the cooperation of the media to educate the public in the uses and desirability forsuch a system. For a ramp metering system, detailed plann ing must demonstrate thatoverall im provem ents to the regional freeway system are not attained by d eterioratingmobility on local arterials, caused by motorists who may choose to by-pass those ramps.Incident management programs are often beset by organizational and institutionalproblem s in the implem entation pha se. Incident man agem ent has becom e a metropolitan area problem affecting a multitude of org anizations, often w ith o verlappingjurisdictions. Ab ove all, a com mitm ent is nee ded to addr ess the problem and takeadvantage of the knowledge, skills and technology that exist to implement an effectiveincident management program.

Bibliography

1. Cambridge Systematics and BSC Engineering, "South Boston Transportation Plan",prepared for the Boston Transportation Department, February 1988.2. Cambridge Systematics, "Incident Management", Final Report prepared for theTrucking Research Institute, ATA Foundation, Inc., October 1990.3. Cambridge Systematics, "Back Bay Transportation Management Study", preparedfor the Boston Transportation Department, Au gust 1990.4. Federal Highway Administration, "Urban and Suburban Highway Congestion,Working Paper No.10", Washington D.C., FHWA , December 1987.5. Federal Hig hw ay Adm inistration, "Quantification of Urban Freeway Congestionand Analysis of Remedial Measures", Report FHWA/RD-87/052, Washington, DCFHWA October 1986.6. Institu te of Transp ortation En gineer s, "Transportation and Traffic Engineer ingHandbook", Second Edition, Washington, D.C., ITE, 1982.



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7. Institute of Transportation En gineers , "Strategies to Al levia te Traffic Congestion",Proceedings of ITE's 1987 National Conference , San Diego, March 1987,Washington, D .C , ITE, 1987.8. Institute of Transportation Engineers, 'Toolbox for Allev iating Traffic Congestion",

1989.9. Scapinakis A. and Ad olf D. May, University of California, "Demand Estimation,Benefit Assessm ent, and Evaluation of On-Freeway High Occupancy Vehicle Lanes:Level 1, Qualitative Evaluation", June 1989.10. Sumner, R. et al, "Freeway Management Handbooks. Volumes 1-4, Washington,D.C, Federal Highw ay Adm inistration, M ay 1983.

Documents

Traff Improvement