Speed Change Distribution of Vehicles in a Highway Work Zone

In response to roadway geometry and traffic control devices, motorists may change their speeds within a work zone. Speed profile data for 102 automobiles (cars and vans) and 49 trucks, which traveled on a section of a traffic control zone 2.4 km (1.5 mi) long, were obtained. The average speeds of automobiles and trucks were 8 to 29 km/hr (5 to 18 mph) and 2 to 19 km/hr (1 to 12 mph), respectively, over the work zone speed limit. Vehicles decreased their speeds to the lowest level near the work space (Route 16 bridge). Even at the work space, about 65% of automobiles and 47% of trucks traveled faster than the speed limit. Automobiles and trucks reduced their speeds by 2 to 21 km/hr (3 to 13 mph) and 5 to 19 km/hr (3 to 12 mph), respectively, compared with their speeds at the beginning of the merging taper. As drivers traveled further into the traffic control zone their speeds first decreased, then slightly increased, and finally reached their minimum value at the work space. After passing it, the speeds continuously increased until vehicles left the study section. Comparisons of speed reductions at similar distances before and after the work space indicated that vehicles attempted to reach the speeds they had before the bridge. The speed reduction distributions for each vehicle group indicated that a small percentage of drivers reduced their speeds by large amounts. Thus, the speed reduction distribution plots were not bell shaped but had long tails (similar to lognormal or Pearson Type III distributions). Statistical analyses based on properties of a normal distribution would not be appropriate for interpretation of speed reduction data for most of the locations within a work zone.