An experiment was carried out on the Road Research Laboratory's track at Crowthorne to determine the effect of various features of cars on the capacity of intersections controlled by traffic signals as determined by saturation flow. It was found that a reduction of the forward visibility of the cars, representative of another type of car produced a decrease in saturation flow of 10 percent at traffic signals with a single lane stop line. An increase in the power weight ratio of 48 per cent, from 54 to 80b.h.p. /ton, for a particular model of car produced an increase in saturation flow 10 per cent. This effect appeared, however, to be largely due to drivers, normally accustomed to driving models with an increased power/weight ratio. A further 10 per cent increase was achieved by using cars with automatic transmission. The corresponding increases for a two-lane approach were 5 per cent. The results indicate that the capacity of intersections controlled by traffic signals and hence of urban streets could be increased by improved performance of vehicles. However, it appears that drivers do not normally use the full capabilities of their vehicles, so the effect in practice might no be as noticeable as in these experiments.
Abstract