Reduction of the number of intersections presents problems in the design of arterial routes and the control of traffic flow more difficult of solution than similar problems encountered on rural highways. For instance, the ideal arterial street would have no intersections, yet it is obvious that all cross streets cannot be closed in order to attain this ideal.
One solution is to eliminate intersections by means of grade separations. Grade separations eliminate the hazards, delays, and costs entailed by encounter with cross-traffic streams. They involve expensive construction, however. A judicious choice of location to minimize the number of intersections is one means of avoiding this expense.
Wherever it is possible to do so with satisfactory accommodation of the local arterial traffic, arterial routes should enter the city at points from which it is possible to proceed as near as desirable to the city center and thence to connection with the continuing rural routes at the opposite side of the city, by locations parallel to one or the other direction of the normal rectangular street plan. Such locations will usually encounter a minimum number of street intersections in traversing the city and are generally to be preferred for this reason. They are also preferable to diagonal or curving locations because of the greater simplicity of the intersections.
Locations adjacent to the usually winding or curving bank of a river or the curved or diagonal line of a railroad should be considered as exceptions to the rule stated above. Such locations usually offer the advantage of protected or infrequent access from one side, and this may offset the disadvantage of greater length within the city and consequent number of streets passed on the other side.
Location in proximity to a railroad is generally considered somewhat objectionable. It need not be, however, if by electrification, the use of Diesel power, appropriate screening and landscaping, or other means, smoke, noise, and unsightliness are abated.
The valley of a small stream penetrating a city may offer excellent opportunity for the location of an intersection-free artery. In many cases such small valleys exist in a wholly undeveloped state. In others they are the locations of a very low order of development—neighborhoods of cheap, run-down houses and shacks, abject poverty, squalor, and filth. ere these conditions exist, steep declines into the valley have generally made the site unfavorable for the development of high-class improvements.
Nor is it entirely accidental that these small stream valleys often lead in directions favorable for arterial routes penetrating from the outskirts of the city to points near its heart. In many cases the original settlement of the city grew up about the junction of these small streams with a larger stream, and the place of the original settlement is the center of the present city.
Often a small valley of this kind interrupts completely or more or less effectively many of the transverse streets. Intercourse within the city has already adjusted itself to crossing at relatively few principal points where bridges have been provided. Under these conditions the valley may provide the most fortunate of opportunities for the location of city-entering arterial routes. Its conversion to
93800—44——-6
