10.4 Factors Affecting Acceptable Gap Distances

Many factors influence acceptable gap distance. When making assumptions about acceptable gap distance, it is important for designers to keep in mind issues summarized in Table 10.2

Table 10.2 Factors that Influence Acceptable Gap Distance
Factor	Impact on Acceptable Gap Distance
Driver Age	Acceptable gap distance for older motorists is about 1 second longer than for younger motorists.
Wait Time	Motorists accept shorter gap distances the as their wait at the stop line increases.
Turn Direction	Motorists accept shorter gap distances when the primary conflicting vehicle approaches from their left.
Road Familiarity	Motorists accept shorter gap distances on familiar routes.
Size of Oncoming Vehicles	Motorists perceive larger vehicles as approaching more quickly than smaller vehicles.
Traffic Volume	As traffic volume increases, motorists generally accept smaller gap distances.
Headlight Glare	When approaching vehicles cast significant headlight glare, motorists accept longer gap distances.

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