indicated in lanes of adequate width is not brought to light by table 17. It is nevertheless true that much of the mileage indicated as having four lanes is actually paved only 36 feet wide and provides, therefore, only three lanes of the width recommended by the Committee; and, similarly some of the three-lane mileage shown as existing is little wider than the width of two lanes of the dimension the Committee recommends.
Assuming adoption of the criterion recommended for the general provision of four or more lanes (viz, average daily traffic exceeding 3,000 vehicles), figure 34 shows the sections of the recommended system that should be improved with pavements of four or more lanes and in comparison shows the existing provision on roads conforming to the system. As will be observed, there are many sections where the greater capacity of four lanes is recommended but where the existing road conforming to the system provides only two or three lanes. On the other hand, a few sections of four-lane pavement shown as existing are located on roads which, according to the recommended criteria, require only a two-lane pavement for adequate improvement.
CONDITION OF CITY STREETS
In the foregoing it has been possible to present a picture in some detail of the physical condition of existing rural highways conforming approximately in location to routes of the recommended system. Of the city streets now serving as connections between the rural highways approximating the system, it is possible to give no similarly detailed account. Judged by the standards proposed, however, existing facilities provided by city streets are so far from adequate that there is little need for detailed analvsis.
Like the rural roads, existing city streets approach nearest to adequacy in the design of their pavements, but a widespread neglect of maintenance has permitted much deterioration of what would otherwise remain as structurally adequate surfaces. In relation to their traffic volumes, many of the city streets have an over-all width less than that provided on some of the rural roads; and, with curb parking a prevalent condition, the width effective for the accommodation of moving traffic commonly compares unfavorably with the corresponding clear width of rural roads.
Intolerable congestion in recent years has forced some effective enlargement of street capacity by the prohibition of parking and the marking of one-way streets. Some minor widening of the vehicular roadways has been achieved also by borrowing slightly from the width of sidewalks. In a few notable cases, such as Woodward Avenue in Detroit, and Constitution Avenue and others in Washington, D. C., broad surface streets have been created by the more heroic means of large-scale property demolition and new right-of-way acquisition.
But instances are rare indeed in which the congestion of through highways in cities has been attacked at its principal root—the frequent grade intersection of cross streets. Instead of eliminating this principal cause of traffic delay, city authorities have generally resorted to the installation of traffic lights for control of the intersecting traffic streams and the prevention of accidents, and this expedient measure has in some cases been so applied as to increase rather than reduce the obstruction of traffic.
