Microsimulation-Based Passenger Car Equivalents for Heavy Vehicles Driving Turbo-Roundabouts

Abstract

Due to its geometric design, turbo-roundabouts impose greatest constraints to the vehicular trajectories; by consequence, one can expect a more unfavourable impact of heavy vehicles on the traffic conditions than on other types of roundabouts. The present paper addresses the question of how to estimate Passenger Car Equivalents (PCEs) for heavy vehicles driving turbo-roundabouts. The microsimulation approach used revealed as a useful tool for evaluating the variation of quality of traffic in presence of mixed fleets (different percentages of heavy vehicles). Based on the output of multiple runs of several scenarios simulation, capacity functions for each entry lane of the turbo-roundabout were developed and variability of the PCEs for heavy vehicles were calculated by comparing results for a fleet of passenger cars only with those of the mixed fleet scenarios. Results show a dependence of PCEs for heavy vehicles on operational conditions, which characterise the turbo-roundabout. Assuming the values of PCEs for roundabouts provided by the 2010 Highway Capacity Manual (HCM), depending on entering manoeuvring underestimation and overestimation of the effect of heavy vehicles on the quality of traffic conditions have been found.

Passenger Car Equivalents for Heavy Vehicles at Roundabouts. a Synthesis Review

“…Based on vehicle movement data collected from video cameras at three large roundabouts accommodating large trucks, also FIGURE 1 | PCE estimations for entry lanes with a similar capacity mechanism (Giuffrè et al, 2016(Giuffrè et al, , 2017(Giuffrè et al, , 2018. Note that roundabout 1 stands for single-lane roundabout, roundabout 2 stands for double-lane roundabout and roundabout 3 stands for turbo roundabout.…”

“…Note that roundabout 1 stands for single-lane roundabout, roundabout 2 stands for double-lane roundabout and roundabout 3 stands for turbo roundabout. (Marino, 2014;Giuffrè et al, 2016Giuffrè et al, , 2018. Note that Q ce and Q ci are the circulating flows in the outer lane and in the inner lane of the ring, respectively.…”

“…Note that Q ce and Q ci are the circulating flows in the outer lane and in the inner lane of the ring, respectively. FIGURE 3 | PCE estimations for left lane on turbo roundabout minor entries with a 10% of heavy vehicles (Marino, 2014;Giuffrè et al, 2016). Note that Q ce and Q ci are the circulating flows in the outer lane and in the inner lane of the ring, respectively.…”

“…Note that Q ce and Q ci are the circulating flows in the outer lane and in the inner lane of the ring, respectively. FIGURE 4 | Capacity functions and simulated data for the right-lane on minor entries at turbo roundabouts (Marino, 2014;Giuffrè et al, 2016). Lee (2015) measured values of headways for differently sized vehicles and values of entry capacity at each site in 1 min fully saturated periods, and estimated PCEs.…”

“…AIMSUN (AIMSUN Dynamic Simulator User Manual, 2011) was used to build several scenarios where entering flows were characterized by different proportions of trucks. For double-lane and turbo roundabouts PCEs were specified by entry lane (Marino, 2014;Giuffrè et al, 2016Giuffrè et al, , 2018. The PCEs resulted increasing as the circulating vehicles increased, especially with high amounts of trucks.…”