![]() ![]() The surrogate 3-s criterion for defining a following platoon is typically based on spot measurements assuming that they are applicable over the entire segment. PTSF is not directly measurable with simple instrumentations in the field since by definition it is a spatial measure over a long highway segment. The Highway Capacity Manual (HCM) has defined PTSF as the average percentage of travel time that vehicles must spent traveling in platoons behind slower vehicles due to the inability to pass ( Transportation Research Board, 2000, 2010). In turn, the percent time-spent following (PTSF) emerged as the most important and widely used traffic measure of performance among traffic practitioners for determining the level of service (LOS) of two-lane highways ( Al-Kaisy et al., 2008 Al-Kaisy and Freedman, 2010). All these interactions ultimately lead to the formation of platoons of fast-moving vehicles behind slow-moving vehicles, subject to a time headway threshold. The geometric variables include available passing opportunities in terms of percent passing zones, dedicated traffic lanes, passing sight distance, and horizontal and vertical alignments. The operational variables include directional distribution of traffic flow levels, vehicular traffic mix with slow-moving heavy vehicles or recreational vehicles, free-flow speed of the highway segment, and driver's aggressiveness factors. Traffic flow on two-lane highways is characterized by some complex interactions among many contributing operational and geometric variables. The results of this research would be useful for a convenient and direct estimation of directional PTSF of two-lane highways. Comparison of the proposed models with the new directional PTSF analytical model of the Highway Capacity Manual shows that the proposed models are capable of predicting simulation-generated PTSF quite closely with absolute mean error <3% using two different sets of validation datasets. ![]() ![]() Both models are based on data generated from the corridor micro-simulation (CORSIM) software. This study proposes two alternative direct models for estimating PTSF: (1) a general linear regression model using typically-used input variables and (2) a non-linear form using only the follower density. However, PTSF is currently estimated indirectly using various measured field data. The percent time-spent following (PTSF) is a key measure for estimating the level-of-service for two-lane highways. Department of Civil Engineering, Ryerson University, Toronto, ON, Canada. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. Archives
January 2023
Categories |