Investigating and modeling speed variability on multilane highways

This paper investigated the speed variance on multilane highways, explored the main associated factors, and developed prediction models to help agencies better set speed limits to reduce speed variance and their associated crashes. Speeds of vehicles were measured for twenty-five multilane highways in Jordan. Data were collected during off-peak hours on sunny days with dry pavement conditions. Results indicated the difference between the design speed and speed limit (DS-SL) is the primary factor that affects speed variance. The minimum speed variance occurs when the DS-SL is 10 km/hr. Speed limits more than 10 km/hr below the design speed increase the speed variance, as road conditions (represented by design speed) tend to control vehicle’s speeds rather than speed limits in these cases. Additionally, having more highway lanes decreases speed variance, as does having roadside barriers. This paper provides beneficial information to authorities and policymakers who set speed limits on multilane highways.