bound traffic. The Survey has cooperated with public officials in the design of a method for traffic regulation on the new drive. The location of the drive will make it possible for drivers moving along it and desiring to cross the river to plan their routes to avoid bridges which may be open. Drivers approaching the river from the south may under favorable circumstances profit similarly.

PHYSICAL CONDITIONS IN THE STREETS THAT HAVE LED TO CONGESTION The first street plan of the city of Chicago was laid down in the year 1830. It covered the territory between and bordering Kinzie, Dearborn, Washington and Jefferson Streets. The citizens of the day were generous and laid down broad streets, eighty feet being taken as a standard. With a number of exceptions, the standard adopted by the original plan has been maintained for the streets of the central business district. The original street plan is shown in Figure 20.

The lack of street area to care for the increasing traffic demands of the city has been the basic reason for the congestion which has developed.

Something of the unbalanced relation between traffic supply and demand that has developed on the streets in the last twenty years is revealed by the figures in Table 15 which show in a comparative manner the increase in paved streets and in motor vehicles in the city. It will be noted that in 1908 there were only 3.8 automobiles for each mile of paved street, whereas in 1925 the number of motor cars per mile of paving had risen to the astonishing figure of 139.

The task of regaining something of an equal balance between street space and traffic demands is for the city planner. There are to be found in the existing streets, however, certain minor physical factors in design or condition, which tend to restrain traffic movement and to result in congestion. Inasmuch as these conditions have a tendency to regulate traffic they are indicated as part of the larger problem of traffic control.

Street design in Chicago, as in every other American city, was made for the days of the horse and buggy. With few exceptions cities continue to lay down streets as though horse-drawn vehicles were still the principal traffic unit. Two factors in design are especially disas

d Decrease caused by eliminating old cedar block pavements from paved streets classification.

trous to the full capacity use of the streets by motor cars. The first is the crown of the roadway. This factor definitely affects street capacity, the driver of the motor truck or passenger car will not tolerate a high crown if he can avoid it. The discomfort of riding at an angle, and the difficulty in steering, especially of trucks, cause drivers on streets with high crowns to stay as close as possible to the center of the roadway. Thus traffic tends to concentrate in the middle of the street, where the slower vehicles exercise a retarding influence on all other traffic. This condition is also brought about by the frequent practice of leaving abrupt humps or depressions in the street surface to accommodate cross drains at intersections. Drivers familiar with

this situation will regularly avoid the lane of traffic nearest the outside of the roadway falling into the procession moving down the center. The gravitation of traffic toward the center of the roadway is encouraged by the smoothness of the pavement. Drivers have learned that comparative comfort is to be found only near the center of the street. On those traction streets where all of the pavement is rough the only tolerable place for travel is along the rails of the surface lines. While the records of paved streets in Chicago as shown in Table 15 indicate that there is at present approximately 2,500 miles of improved roadway, these figures are distinctly misleading. A considerable amount of the earlier type of city pavement has become so roughened by heavy wear and other disintegrating forces that it can no longer be classified accurately as suitable surface for modern automotive traffic. No factor has a greater importance in the concentration and congestion of traffic, or in its proper distribution and freedom of movement than attractive pavement. Traffic is much like water. It flows where there is a natural attraction. Smooth pavement affords this attraction. Aside from the boulevards, and several rare examples of modern construction, Chicago woefully lacks good traffic streets. The most direct physical relief that could be brought to the Chicago traffic problem would be an energetic and comprehensive paving program. The streets of the world's fourth metropolis should be at least as smooth as a modern rural highway. Mileage of various street improvements is shown in Fig. 21.

If the pavement on all streets leading from and surrounding the central business district were improved, there would be a much more even distribution of traffic, and a diversion of much traffic that now finds it necessary to go through the crowded sections of the city in order to find comfortable roadway surface.

One of the most glaring faults in former street design from the standpoint of automotive use is the antiquated curb return. The horse and buggy moved at a comparatively low rate of speed, and could turn quite sharply, thus there was no reason why the curbs at intersections should be rounded. Automobiles move at a greater average rate of speed, and their design makes it impossible for them to turn at a sharp angle. Larger vehicles in making right turns at intersections must swing out toward the center of the roadway before reaching the corner, or must swing to the left side of the cross street. At the intersection of