One of the major factors that should be considered in selecting the speed limit for a stretch of
highway is safety. It is generally accepted that the level of safety depends on certain
characteristics of the traffic stream and the geometric alignment of the highway. However, in
many cases speed limits are posted without adequate consideration given to these
characteristics. For example, an important traffic characteristic that influences safety is speed
variance. Currently, little is known about the factors that affect the variance of vehicle speeds …

A study was conducted to investigate the traffic engineering factors that influence speed
variance and to determine to what extent speed variance affects accident rates. Detailed
analyses were carried out to relate speed variance with posted speed limit, design speeds,
and other traffic variables. The major factor identified was the difference between the design
speed of the highway and the posted speed limit. It was determined that speed variance will
be minimal if the posted speed limit is between 6 and 12 miles per hour lower than the …