The stability of driver acceleration behavior, and a replication of its relation to bus accidents.

The reliability over time of a method for measuring driver acceleration behavior was tested on bus drivers in regular traffic. Also, a replication of an earlier finding of a correlation between driver acceleration behavior and accident frequency for the individual drivers was made. It was found that the split-half correlation is probably around 0.50 for the mean (of accelerations) of a 30-min drive, and similar for the test-retest of 2.5h measured about a month apart. With such reliability, the sample was probably too small to reliably determine any association with accidents, but some significant correlations were found. Some ways of holding constant the differences in exposure and driving environment were tried with mixed success. Alternate ways of analyzing the data and several methodological problems were briefly discussed. It was concluded that the measurements of acceleration behavior, for bus drivers, are fairly reliable over at least a few months. However, some strange discrepancies between samples make all interpretations concerning the link to accidents tentative.