A study of traffic capacity

The results of a traffic capacity study started in june 1934 by the traffic bureau of the ohio state highway department are presented. The data were collected by the photographic method described in volume 13 of the PROCEEDINGS OF THE HIGHWAY RESEARCH BOARD. After a brief description of the method of collecting and tabulating the information, certain selected data are analyzed to secure a measure of the working capacity of a two-lane roadway and the amount of vehicle time lost under varying degrees of congestion. The study of 1180 groups of 100 vehicles each, including not over 10 percent trucks, reveals the average free moving speed to be about 43 miles per hour on either a two or three lane road. When the number of vehicles exceeds 400 to 600 per hour, the average speed decreases and the effect of a few slow-moving vehicles is more pronounced. The mean speed of 859 light trucks was 41.0 miles per hour, and of 225 heavy trucks, 32.4 miles per hour. for 18 buses, the average was 41.6 miles per hour. In the discussion, Mr. Bibbins discusses the method of obtaining over-all speeds over a stretch of highway by recording the tag number of the vehicle entering the stretch and checking the same tag number on leaving. Mr. Canning describes a method of obtaining average running speed. Mr. Miller discusses measurement of traffic delay by traffic counts and the progress of an automobile in traffic. The record of progress is obtained by means of an instrument attached to the automobile which marks a graduated ribbon indicating the speed of the vehicle and the time loss due to cross traffic, stop lights, slow moving traffic, congestion, road conditions, etc. In Pennsylvania, a number of touring cars were equipped with Recordographs that indicate the speed of a car graphically on a ribbon. The Recordograph traffic analysis was found to be an accurate method of determining the traffic capacity of highways and valuable aid in determining traffic conditions.