EXPERIENCED TRAVEL TIME DIFFERENCES AND AVERAGE SPEEDS - FACTORS WHICH MAY BE ASSUMED TO AFFECT THE SPEED DEMANDS OF DRIVERS

The effect of the speed on the travelling time is a factor which may be assumed to be a central part of the driver's speed demands. This report states the results of several investigations showing that persons overestimate - when being presented different distances and speeds in a symbolic form - the effect on the travelling time of a given acceleration of the high speed levels compared with the low speed levels. Similar results have been obtained in an investigation where the subjects were visually presented actual speeds and distances in a laboratory experiment. Finally the results of an investigation were presented where the subjects were supposed to estimate the mean speed of different visually presented speeds on distances of different length. This was also a laboratory experiment and the results indicate that people generally overestimate the average speeds. The way these divergences of objective and subjective differences in the travelling time and the mean speeds may affect the drivers speed demands are discussed in this report. /TRRL/