Quantifying How Much Key Factors Influence Freeway Operational Speeds During Noncongested Periods

Abstract

An evaluation of speeds on Texas freeways used data from 243 roadway sensors located in Fort Worth representing operating speeds during daytime and clear weather conditions from 2015 to 2019. The initial evaluation explored how much average operating speeds increased when the posted speed limit (PSL) was raised from 60 to 65 mph, 60 to 70 mph, or 65 to 70 mph. The average operating speed increased between 2.4 to 4.0 mph for 5-mph increase in PSL or 2.9 mph for the 10-mph increase in PSL. The next evaluation identified variables associated with variations in average freeway speeds. The most significant amount of operating speed variation was associated with unidentified localized factors representing 33.8 percent of variability due to differences between detector locations. Yearly shifts in speeds at a given location were found to be the third most relevant source of speed variation (10.6 percent). Geometry was estimated to explain about 7.5 percent, speed limit 4.1 percent, and citations 3.6 percent of the speed variation in this dataset. Geometry, citations, and PSL represent the range of influence for engineering, law enforcement, and traffic management on operating speed. This study estimates that a strategy that entails modifying geometry, changing the PSL, and varying the level of law enforcement presence within the ranges included in this study may impact freeway operational speeds up to 6.2 mph (depending upon existing conditions along with the changes in the geometry, PSL, and enforcement).