In many cities the surface location of railways remains as one of the more acute problems facing the city planner. Instead of attacking this problem piecemeal by elimination of grade crossings one or two at a time, a practice which tends merely to ameliorate a generally unsatisfactory condition, it would be far better if it were dealt with in accordance with a plan for the complete and permanent insulation of the railway. Since the interregional routes and other express highways require, in some degree, a similar insulation, a plan for the common location of the two facilities might offer not only the advantage of a minimum obstruction of cross streets but also a substantial possibility of reducing the total costs of achieving the two purposes, particularly the right-of-way element of such costs. A striking development of this character in the city of New York is illustrated in plate I.
Relation to contemplated developments requiring large tracts of land.—Wherever it is possible to do so, the location of interregional routes in cities should be considered simultaneously with the projected location of new housing developments, city centers, parks, greenbelts, and other contemplated major changes in the existing city pattern that call for the acquisition of land in large tracts. This is necessary for the avoidance of conflicts in plans; it is necessary from the standpoint of adequate transport accommodation; and it is highly desirable from the viewpoint of common land acquisition and financing. The location of express routes within or adjacent to such areas may be one of the most fruitful means of avoiding street intersections, but should only be applied subject to a proper regard for the character, uses, and needs of the several areal developments.
Minimization of street intersections.—In the operation of motor vehicles we are conscious today as never before of the rubber-and-gasoline costs of stopping and starting.
Investigations by the Iowa State College on the wear of tires show, for example, that at the wartime maximum speed of 35 miles an hour, a single stop and start normally wears away about as much rubber as a mile of travel.
Other investigations by the Iowa college have determined that at the same wartime speed, a single stop and start by an average passenger car consumes as much gasoline as 0.15 mile of driving on a straight highway of average gradient.
Under any circumstances stopping-and-starting costs constitute tangible amounts worth saving.
The frequency of street intersections is the cause of excessive stops and starts in cities. Every intersection also introduces substantial elements of delay and congestion.
If the permissible speed of moving traffic is 35 miles per hour, a halt of only half a minute at a traffic light consumes time in which each halted vehicle, but for the stop, would have advanced nearly 4 average city blocks. On a street carrying a daily traffic of 10,000 vehicles, if this traffic were equally distributed throughout the 24-hour day, one such traffic light operated on a half-minute interval would prevent 739 vehicle-miles of movement in a single day.
These calculations ignore the time lost in starting and stopping. If this also were subtracted, the total daily loss of vehicle-mileage might easily be doubled, and 10 lights under these conditions might rob the entire traffic stream of nearly a mile and a half of movement daily.
