A STUDY OF FACTORS INFLUENCING TRAFFIC SPEEDS

The over-all objectives of the research project were (a) to evaluate the effectiveness of speed limits established by present practices and (b) to develop new or more substantial criteria for the establishment of speed zones. The results of the first phase of the research were reported previously. This report covers the second phase of the research and deals specifically with an evaluation of factors influencing the drivers' selection of speed The first part deals with a study of factors that influence traffic speeds m areas of transition from rural to urban conditions Two study techniques were used to measure speeds in transition areas: (a) measurement of the average speed of each vehicle through each of several sectors of the transition zone, and (b) continuous measurement of the speed of a test car through the transition zone. The studies pointed up several roadway and development characteristics that influenced traffic speeds, including horizontal and vertical curves, sight distance, changes in roadway cross-section, commercial development, and appearance of residential development. Several studies involving 12and 24-hr speed observations were conducted to determine the influence of changing traffic conditions on traffic speeds. These studies showed that speeds were subject to only minor variations during the hours of normal traffic operation Other studies were concerned with the influence of radar enforcement operations on traffic speeds. These studies showed that enforcement operations caused appreciable speed reductions, but the influence did not extend beyond four miles on either side of the enforcement unit.