Chapter IV

DETAILED ANALYSIS OF SURVEY FINDINGS In the preceding chapter, a series of summary

pictures was presented. In combination, these maps provided a description of the major pat­terns of traffic desire and related these patterns to the land development. These totals tell much about the area's traffic. However, many impor­tant details are necessarily hidden. To plan effectively for the area's road needs, detailed in­formation about traffic desire is essential. In this chapter, the significant parts of the entire traffic desire pattern will be isolated and described. With such a large volume of data, there are in­finite ways of grouping the material. Therefore, only the most significant parts are selected. The discussion of traffic desire is organized by direc­tion of travel, by vehicle type and by mode of travel so that sources of travel and the amount of desire at different points in the area will be clear. In reading these maps it must be remem­bered that all patterns result from moving the traveller on a "bee line" from his origin to his destination. The patterns do not follow the route which the traveller may actually have taken.

Vehicular Trip Desire Vehicles move both persons and goods. Ve­

hicles, therefore, are the unit best adapted to measure the demand for roadways. Vehicle movements are described first. Then truck move­ments are separately shown and finally, the pat­terns of passenger trips are illustrated to com­plete the total travel inventory.

Vehicle travel desire is described in two ways in the following maps. First, a distinction is made between the local and the external trips. Local trips both begin and end within the Study Area. External trips enter and leave the Area. Local trips are made in carrying on the internal commerce of the Area, while the external trips represent the import-export relationships of the

Study Area with the outside world. The all-ve­hicle movement shown on Map 7 above is now divided into two parts: Map 10 showing ex~

ternal vehicle trips and Map 11 showing in­ternal vehicle trips.

A second distinction is then made between trucks and total vehicles. The truck travel de~

sire is separately plotted showing the external travel on Map 12 and the internal travel ·on Map 13.

Internal and External Vehicular Trip Desire Patterns

Map 10 shows the pattern of desire line den­sity for all external vehicle trips. The internal trips are represented on Map 11 at the same scale so that the two patterns can be compared.

To understand how these maps are prepared, imagine that a pin is placed in the map at the point of origin and at the point of destination for each trip.1 Then, suppose a rubber thread were stretched between every pair of pins. Meas­ures of desire intensity are obtained from a count of the number of "threads" over any single square which was one-half mile long on each side (or four squares in a square mile) . Isolines are then drawn to group areas of like de­sire line intensity. In the case of external trips shown on Map 10, these rubber threads were pinched together according to the particular point on the cordon line where the driver was interviewed. Then, only the travel desire be­tween this point on the cordon line and the in­ner trip end was counted and illustrated.

One glance at these two maps shows that the bulk of the traffic is caused by the local trips. Of the 3,630,000 trips represented on the two maps, only 254,000 or 7 %, are external trips.

lFor a more detailed discussion, see page 105 Appendix.

49

·.

'' .

·,., ---+-....J

·' ,• .

" . ' '

··· ·.;

50

LAKE ERIE

DETROIT TRAFFIC STUDY AREA

TRIP DESIRE CHART

LAKE

STCLAIR

LEGEND

This chart s hows the pattern of

travel desire of 254,229 vehicle

trips which crossed the cordon

line on on a verage weekday in

t he fall of 1953. A tota l of

3,055,501 a i rline miles are

traced on this chart to represent

the external vehicle travel de­

sire. All desire lines are traced

through a one-half mile grid

system.

Desire line Traces Per Quarter Square Mil•

CJ 24,000 to 28,128

CJ 16,000 to 23,999

D D D

12,000 to 15,999 8,000 to 11,999

4,000 to

2,000 to

7,999

3,999

08ROIT M8ROPOLITAN AREA TRAFFIC STUDY 1955 181

EXTERNAL VEHICLE TRIPS

Mop 10

l

LAKE

ST CLAIR

LEGEND

- Desi re Line Traces Per Quarter Square Mile

100,000 to 102,205 This chart shows the pat- - 90,000 to 99,999

80.000 to 89,999 tern of t r avel desi re of 70,000 to 79,999 3,375,370 vehicle trips in- 60,000 to 69,999 s ide the cordon line on an

50,000 to 59,999 average weekday in the

fall of 1953. D 40,000 to 49,999

D 32,000 to 39,999 A total of 13,185,627 a ir-

D line m iles are traced on th is 24,000 to 31 ,999

chart to represent the inter- D 16,000 to 23,999

nal vehicle trav e l desire. D 12,000 to 15,999

All des ire lines are traced 8,000 to 11,999

th ro ugh a one-half mile D 4,000 to 7,999

grid system. 2,000

DHROIT MHROPOliTAN ARfA TRAttiC STUDY LAKE ERIE 1955 Ill

• DETROIT TRAFFIC STUDY AREA

TRIP DES IRE CHART

INTERNAL VEHICLE TRIPS 51

Map 11

.·.

' .

-~-------

External trips, covering greater distances inside of the Study Area, however, account for 19% of the desire line miles shown on the two maps.

EXTERNAL DESIRE

The external trips have special significance because these are the trips which are the principal users of the interstate highways and, therefore, provide clues as to t~e need for such routes interconnecting the Detroit Area with other cities and metropolitan areas.

The eight places where the federal interstate routes cross the cordon line and the bridge and tunnel to Canada accounted for half of all ex­ternal vehicle trips. Another quarter were on eight state routes, and the remaining quarter were on the twenty-seven local roads. ·

The external travel desire shows that a very small portion of these trips go through the area without stopping. Actually, of the 254,229 ve­hicle trips counted on an average weekday, only 8,068, or three percent, go through non-stop. The principal movement of this kind can be seen on the west side of Detroit. The survey showed that 1,682 vehicles went completely through the area on U.S. 24, Telegraph Road. Yet, even here it is clear that most vehicles enumerated at South Telegraph Road had travel desires oriented towards Detroit. Of the 2 1, 180 vehicles entering and leaving at this point, only eight percent continued non-stop through the area. The bulk clearly had terminal points within the Study Area.

Through, non-stop travel is such an exceed­ingly small part of the total traffic intercepted that some special comment is warranted. A glance at maps 1 and 2 will disclose why this is so. Detroit is not on any major line of inter­state travel. Also its location at the edge of the United States and at the edge·of the Great Lakes shoreline indicates that any traffic found in the area is most likely to be going to or coming from the Detroit Area. It is clear from these facts that the Detroit Area is a place to be gotten to

52

rather than around.2

The external trip desire density dissipates rap­idly with distance from the roadside station. This is not because the part of the trip inside the area is short. Actually, the average desire length is nearly twelve miles inside the Study Area. The rapid dissipation of density is due primarily to the diversity of the internal ends of these trips. Desire lines fan out from the sta­tions to a variety of internal points, thus reduc­ing the desire density as the lines spread apart. The principal feature of this entire map is that travel from all points along the rim of the Study Area is directed principally towards the heart of the area in the center of Detroit.

INTERNAL DESIRE

Map 11, showing the accumulated desire lines of internal trips demonstrates the effect of the high intensity of land use in and near the Central Business District. Ever-increasing volumes are shown as the center is approached. This de­scribes a steadily mounting traffic pressure on facilities to a climax at the Central Business District (area of darkest red) . In the heart of the Central Business District, nearly half of the entire land is in streets and alleys ( 46.5%) and an additional nine percent is devoted to parking lots and garages.

From the dense core of traffic (the area col­ored red) fingers of heavy desire volumes can be observed extending outward. This is due to the previously noted effects of the land usage ex­tending outward along the radials. Sub-pat­terns can be observed for communities such as Wyandotte to the south, West Dearborn on the west, Ferndale, Royal Oak, Berkley and Bir­mingham out the North Woodward axis and Mount Clemens in the northeast corner of the map. All of these appear as "islands" with higher than average travel intensity outside of the Detroit mass.

This map shows how the increasing vehicle volumes can place strain on the roads of the

2Map 36 in the Appendix shows the major through move­ments and their volumes.

area and provides a generalized picture of those places where demands are greatest. It is obvious that these internal trips constitute the real bulk element of the traffic problem.

Truck Movement Patterns Maps 10 and 11, representing all vehicle

movement, actually have both trucks and pas­senger cars included. It is possible to deal with vehicles in an undifferentiated way because pas­senger cars and commercial vehicles are mixed into an average pattern and because passenger cars, representing 85% of all vehicle trips, are the dominant element. Map 12 shows the pat­tern of external truck trips in exactly the same fashion as Map 10 showed all external vehicle movement. Likewise, Map 13, showing in­ternal truck movement, can be compared with Map 11 showing internal desire line movement of all vehicles. Both truck desire line charts are constructed at intervals which are 15% of the interval values used to describe movement of all vehicles. This allows comparison of the pat­terns of trucks with the movement of all ve­hicles.

While these charts deal with the differences between movement of trucks and of total ve­hicles by location and magnitude of desire line volumes, trucks also differ from the hourly pat­terns of passenger cars. Truck movement throughout the day is described in Figures 1, 2 , and 3. Trucks tend to move heavily during the off-peak times of passenger car movement. Thus trucks, by virtue of their use and the pro­gramming of the shippers, are not as significant a part of the peak movements as they are of the .total movement. While nearly 15% of all trips are truck trips, only 11% of the vehicle trips during the peak hour ( 4:00 P .M.-5: 00 P.M.) are by trucks.

The term "truck" covers a variety of vehicle types. Trucks yary from the light delivery truck (panel or pickup) which is equal to a passenger car in street occupancy to the tractor­trailer combinations which may be equivalent

to as many as four passenger cars in street space occupied. The division of trucks into types helps in evaluating their importance in the traffic streams.

All internal trucks were classified into three principal types : light trucks, large single unit trucks and combinations. Summarizing these groups, the trips and mileage of desire line travel is shown in Table 15.

TABLE IS- PERCENTAGE DISTRIBUTION OF INTER­NAL TRUCK TRIPS AND TRUCK MILEAGE ACCORD­

ING TO BODY TYPE

Average Percent of Percent of Number of Total Trips Total Miles Minutes

Enroute per Trip

Light trucks . .. . .. . 51.7 51.8 16.4 minutes Heavy single units . 42.9 39.8 16 .6 minutes Combinations . . . . • . 5 .4 8.4 33. 7 minutes

Total. . .. , . . . . 100 .0 100. 0 17·, 5 minutes

From this table, it can be seen that only a por­tion of the total internal truck trips are by the heavier trucks although these trucks are on the roads longer than are the lighter trucks. Ex­ternal trucks, on the other hand, have 34% of their trips made by light trucks, 28.4% by heavy single units, and· 37.6% by combination units. With these qualifications in mind, it is possible to compare the spatial patterns of truck desire movement with that of total vehicles.

EXTERNAL TRUCK DESIRE

The desire patterns of external trucks, while generally similar to that of all vehicles, shows some major differences. There is a particularly heavy truck movement on South Telegraph (U.S. 24, 25) to and from Toledo and on the Industrial Expressway (Michigan 112) head­ing to and from Chicago. Also truck travel in­side the area focuses on the terminal areas in East Dearborn in the vicinity of the Ford Rouge Plant. This is in contrast to the heavier orien­tation of passenger cars towards Detroit's Cen­tral Business District. It is also possible to identify a heavy truck movement corning down

53

•, ..

··' .

•'•· .

54

. ·.

LAKE ERIE

DETROIT TRAFFIC STUDY AREA

TRIP DESIRE CHART

b

LAKE

ST CLAIR

LEGEND

Desire line Traces This chart shows the pattern Per Quarter Square Mile

af travel desire of 40,002

truck trips which crossed the

cordon line on an average

weekday in the fall of 1953.

A total of 541,714 airline miles

are traced on this chart to rep­

resent the external t ruck travel

desire. All desire lines a re

traced through a one-half mile

grid system.

D D D D CJ CJ D

6,000 to 7,177

4,800 to 5,999

3,600 to 4,799

2,400 to 3,599

1,800 to 2,399 1 ,200 to 1 ,799

600 to 1,199

300 to 599

OHROIT MfTROPOLITAN AREA TRAffiC STUDY 1955 Ill

EXTERNAL TRUCK TRIPS

Mop 12

•

-

• LAKE ERIE

DETROIT TRAFFIC STUDY AREA

TRIP DESIRE CHART

LAKE

ST CLAIR

LEGEND

This chart shows the pat­

tern of travel desire of

419,370 truck trips inside

the cordon line on an aver-

age weekday in the fall of

19 53. A toto I of 1,406,044

airline miles are traced on

th is chart to represent the

interna I truck travel desire.

All desire lines are traced

Desire line Traces Per Quarter Square Mile

- 10,500 to 11,020

- 9,000 to 10,499

- 7,500 to 8,999

0 6,000 to 7,499

D 4,800 to 5,999

CJ 3,600 to 4,799

D 2,400 to 3,599

1,800 to 2,399 1,200 to 1,799

through a one-half mile c=J grid system.

600 to 1,199

300

DETROIT METROPOLITAN ARfA TRAFFIC STUDY 1955 Ill

INTERNAL TRUCK TRIPS 55

Mop 13

Van Dyke (Michigan 53) to the produce ter­minals just east of the Central Business District.

Trucks show a much greater tendency to­wards through movement on the west side of Detroit on U.S. 24. Actually, of the 1,682 ve­hicle trips through the Study Area on this route, 765 or more than 45% were truck trips.

The external truck travel is a large propor­tion of the total truck movement. External trucks account for 28% of the combined in­ternal and external truck desire line miles.

It is also clear that the trucks are selective in the routes they use. This can be seen by com­paring the truck map, # 12, with the external all vehicle desire map, # 10. For example, trucks constitute 14% of the vehicles on M-97 as opposed to 11% on U.S. 25 (Gratiot Ave­nue), 22% of the vehicles on North Telegraph as opposed to 14% on Woodward A venue and 20% on the Industrial Expressway (M-112) as opposed to 10% on Michigan Avenue. There is a heavy truck movement south to the major manufacturing cities of Toledo, Cleveland, Pittsburgh and others on South Telegraph Road. At this station just over one-third of all vehicles were trucks, making it the most heavily travelled route entering the area from a standpoint of truck volume.

INTERNAL TRUCK DESIRE

Map 13, showing internal truck desire, is con­structed so that it can be compared with Map 11. Differences in the patterns will demonstrate the extent to which truck patterns differ from the patterns of passenger cars. In general, the two maps are quite similar. Both have the char­acteristic build-up in trip intensity as a conse­quence of the more intensive land development towards the center.

The truck travel map has less area within the high volume isolines. This results partly from a difference in destination density but largely from the fact that truck trips are shorter than pas­senger car trips. The amount of area on any map within a given isoline is a function of not

56

only the number of trips but also their length. Trucks also appear less prone to concentrate

in the central areas. Notice that the area of dark yellow covers about the same territory on both Maps 11 and 13. With these few exceptions, the desire line patterns of trucks have very great similarity to that of all vehicles. In both maps, the intensive land use areas at the center of De­troit and at the New Center Area produce the most concentrated trip volumes. It is probable that much of this similarity is due to the pre­dominance of light truck trips which have pat­terns similar to the automobiles.

The data on truck travel point up the follow­ing significant facts:

1. Truck travel is heaviest between the peak periods of passenger car travel.

2. The large, combination trucks are pre­dominantly used in intercity travel and, therefore, are of most significance in the external pattern.

3. Internal truck trips have very similar pat­terns to the internal passenger cars.

It follows from these facts that the peak traffic volumes for which streets must be designed (a peak hour on a weekday) are not severely affected by truck movement. If the travel needs of all vehicles are met, then truck movement will be well served. Thus, for planning purposes in the Detroit Area, traffic demand is well repre­sented by considering the undifferentiated total vehicle travel desire.

This conclusion does not imply that trucks are unimportant. It does say that if adequate facil­ities can be planned to meet the demands rep­resented by all vehicles, such plans will give pro­portionate relief to truck travel.

Person Travel Desire Patterns The preceding sections have been concerned

with the travel patterns of vehicles. The pre­dominant element in the vehicle pattern is the passenger car. Since passenger car move­ment results from the need for people to move

about, knowledge of the volumes, the sources and the nature of person movement is necessary to understand and to predict vehicular move­ments.

Passenger cars are principally involved in moving people. But all people are not drivers. People travel as drivers of passenger cars, as passengers in cars, as riders on the mass transit system, and they walk. These four travel modes account for nearly all person movement.

The ability of persons to move freely at low cost is a basic condition for the existence of a metropolitan community. Therefore, the provi­sion of the proper kinds of facilities to meet the great demand for person movement is one of the largest and most perplexing of urban prob­lems.

As persons choose alternate means for get­ting about, it is obvious that the use of auto­mobiles has been an increasingly popular choice. If this trend continues, the streets, the parking facilities and the other fixed inventories for such movement will be placed under increas­ing stress. Since the population is also increas­ing, growth in demand for facilities for autos is correspondingly accelerated. To insure ade­quate facilities for present and future vehicle movement, it will be essential to know enough about this huge reservoir of person movement and the means of travel selected so that proper steps can be taken to ~upply the needed facil­ities.

DRIVERS VERSUS AUTO PASSENGERS VERSUS TRANSIT PASSENGERS

Generally, people travel in one of four ways as set forth above. Detailed inventories were made of trips by auto drivers, auto passengers and transit riders. It was not possible to inven­tory walking trips (although walking trips to work were recorded). While some walking trips are potentially trips by other modes, for the most part they are an exclusive kind of per­son movement. They are such short trips and so specialized that conversion to driver or rider trips is most unlikely.

Person movement on an average weekday in the Area was enormous. A total of 5,694,901 person trips were counted and these persons traveled a total distance of 25,736,552 miles measured as the crow flies. Of this total, auto drivers accounted for 56% of the trips and 55% of the mileage. A summary of this per­son movement is presented in Table 16.

TABLE 16- SUMMARY OF TOTAL PERSON MOVEMENT IN THE SURVEY AREA ON AN AVERAGE WEEKDAY

BY TYPE OF TRIP

Total Average Total Desire Desire

Type of Trip Trips Line Line Reported Miles Miles

Traveled in Area

External Trips Auto Drivers . . .•... . •. . 215 ' 713 2 ,531,408 11.7 Auto Passengers ....... . 215,213 2,650 ,806 12.3

Total External. .• . . . 430,926 5 ,182,214 12.0

Internal Trips Auto Drivers .. .• . . ... . . 2,990,485 11,582,573 3 .9 Auto Passengers 1

• •• •••• 1,394,265 5 ,276 ,303 3 .8 Mass Transit Passengers. 879 ,225 3,695,462 4 .2

Total Internal . .• .... 5,263,975 20,554,338 3 . 9

GRAND TOTAL • . . 5,694,901 25,736,552 4.5

1 Includes some 31,910 passeng~rs in trucks and taxis.

Interviews of residents disclosed that during an average weekday nearly two out of every three persons aged 5 or over make trips in autos or on public transit vehicles and these travellers average nearly three and one-half trips each. The choice of a means for performing this travel depends upon availability of cars, the place of origin and destination, the time of day and many other factors.

The outlines of the spatial patterns and den­sities of internal auto driver trips have already been shown on Map 11. In the following pages, comparable desire line patterns of transit pas­sengers (Map 14) and auto passengers (Map 15) are presented. The three maps are drawn at nearly identical scales and show three distinct spatial patterns of travel. Auto passengers are spread throughout the Study Area most evenly. Transit passengers show extreme concentration of desire at the heart of the area. The auto

57

58

\ LAKE ERIE

DETROIT TRAFFIC STUDY AREA

TRIP DESIRE CHART

t

LAKE

ST CLAIR

LEGEND

This chart shows the pat­

tern of travel desire of

875,630 mass transit pas­

senger trips inside the cor­

don line on an average

weekday in the fall of 1953.

A total of 3,701,541 air­

line miles are traced on

this chart to represent the

mass transit passenger

travel desire. All desire

lines are traced through a

one-half mile grid system.

Desire line Traces Per Quarter Square Mile

- 70,000 to 140,485

• 60,000 to 69,999

40,000 to 59,999

D 32,000 to 39,999

D 24,000 to 31,999

D 16,000 to 23,999

D 12,000 to 15,999

D 8,000 to 11,999

D 4,000 to 7,999

D 2,000 to 3,999

500

OHROIT MHROPOLITAN ARfA TRAttiC STUDY 1955 Ill

TRANSIT PASSENGER TRIPS

Map 14

•

LAKE

STCLAIR

--LEGEND

This chart shows the pattern Desire line Traces of travel desire of 1,338,635 Per Quarter Square Mile , .. auto passenger' trips inside D 32,000 to 34,895 the cordon line on an aver·

D age weekday in the fall of 24,000 to 31,999

1953. A total of 5,065,796 D 16,000 to 23,999 airline miles a re traced on

D this chart to represent the 12,000 to 15,999

auto passenge r travel desire, D 8,000 to 11,999 All desire lines a re traced

D 4,000 7,999 through a one-half mile grid

to

system. D 2,000 to 3,999 l lncludes 31,900 Truck Qnd Taxi

500 passengers.

OHROIT MHROPOLITAN ARfA TRAFFIC STUDY \ 1955 Ill

DETROIT TRAFFIC STUDY AREA

TRIP DESIRE CHART

INTERNAL AUTO PASSENGER TRIPS 59

Map 15

·.' . '

.. : ,.·

drivers fall in between these extremes, having more of a central focus than auto passengers but less than transit passengers. By looking a little closer at the two passenger maps, the rea­sons for the different patterns and some of the selective factors which influence the traveller's choice of transport can be understood.

Transit Passengers

There are 880,000 transit trips on an average weekday in Detroit. This is 17% of the totaJ internal trips shown. However, 25% of all the workers in the area use public transit to get from home to work and 50% of all persons travelling to the Central Business District travel by public transit.

As these facts suggest, transit riders have unique patterns in time and in space. Heavy usage for travel to work produces very marked peaks in the daily riding habit of transit pas­sengers. Figure 3 shows the percentage dis­tribution by hour of trip beginning throughout a twenty-four hour period for transit riders, auto drivers, auto passengers and truck drivers.

These are four completely different patterns. For auto drivers, the non-work trips build to a peak during the hour beginning at 7:00 P.M. But the peak volumes of auto driver trips occur from 7:00 to 7 :59 A.M. and from 3:00 to 5:59 P.M. Thus, the peak vehicle flows are di­rectly chargeable to work travel.

The auto passenger chart shows a low morn­ing peak, then a steady rise in the number of trips to the dominant peak during the hour be­ginning at 7:00 P.M. Non-work trips have a much more marked peak at this hour. This oc­curs because· most family cars are home at this time of day. This is the time when the husband runs an errand and takes riders along or the family takes an excursion. Also affecting this peak is the previously demonstrated low load­ing factor for persons driving to work. Few drivers to work have riders. Heaviest car load­ing is for social-recreational trips and these are most frequent after dinner and after work.

60

Transit trips show extremely sharp peaks. This is one of the greatest causes of the transit industry's difficulty. While the peaks are mostly due to work travel, the non-work travel also has sharp peaks. These non-work peaks are pri­marily due to the heavy use of the bus by school children-especially in the outer suburbs. It may also be possible that some non-work trips are induced during the peak hours because of the more frequent service on bus lines at that time.

Truck trips have the most even time distribu­tion of all modes. The truck travel, being per­formed by persons at work, occurs mainly dur­ing the normal eight-hour work day. The peaks do not occur at the same time as the auto driver trips.

It can be seen that the vehicle movement problem is greatest during the afternoon peak hours and that this is very largely due to the un­even distribution of work travel. To the extent that peak hour flows are the controlling fac­tor in determining the capacity of a street sys­tem, work travel is the most important element.

Transit trips also show selectivity in space. The pattern on Map 14 is sharply different from the pattern of other maps. Travel desire is much more tightly grouped toward the city center. The dense travel is concentrated within a very small area. This, of course, is both cause and effect. The transit lines cannot extend economically into the more sparsely settled suburban areas. So the pattern is partly a result of the availability of transit service which, in turn is partly due to the thinness of travel desire volumes in the outer parts of the Study Area.

The great concentration of transit riders at the center is indicated by the area of darkest red. Extremely high peak volumes are regis­tered at this point. Similar peaks but not so high can be noticed at the junction of Woodward A venue and Grand Boulevard and at industrial plants such as the River Rouge Plant and the east side industrial concentrations at East Jefferson and Milwaukee Junction.