This paper presents an empirical investigation into performance indicators on two-lane rural highways. Field data from four study sites in the state of Montana were used in this investigation. Six performance indicators were investigated in this study; average travel speed, average travel speed of passenger cars, average travel speed as a percent of free-flow speed, average travel speed of passenger cars as a percent of free-flow speed of passenger cars, percent followers, and follower density. The study examined the level of association between the selected performance indicators and major platooning variables, namely; traffic flow in the direction of travel, opposing traffic flow, percent heavy vehicles, standard deviation of free-flow speeds, and percent no-passing zones. Among all platooning variables investigated, traffic flow in the direction of travel was found to have the highest correlation with performance indicators. Other platooning variables only exhibited weak correlations with performance indicators. Also, follower density and percent followers exhibited the highest correlations with platooning variables respectively. An obvious advantage of using follower density is the fact that this performance indicator accounts for traffic level which is a major determinant of performance on two-lane highways.
Abstract