Variables influencing spot-speed characteristics

160 articles are included in this review which is divided into five basic groups: driver, vehicle, roadway, traffic and environment. The articles seem to indicate that of the driver variables, trip distance has the most significant influence on spot speed. Type and age of vehicle are also predominant in their effect on spot speeds. In the area of roadway characteristics, those of classification, curvature, gradient, number of lanes, and surface type tend to be of significant influence. Traffic density and vehicle volume dominate the traffic variables and the important environmental factors are usually time and weather insofar as spot speeds are concerned.