Effects of longer heavy vehicles on traffic congestion

Abstract

Two-lane, ''microscopic'' (vehicle-by-vehicle) simulations of motorway traffic are developed using existing models and validated using measured data from the M25 motorway. An energy consumption model is also built in, which takes the logged trajectories of simulated vehicles as drive-cycles. The simulations are used to investigate the effects on motorway congestion and fuel consumption if ''longer and/or heavier vehicles'' (LHVs) were to be permitted in the UK. Baseline scenarios are simulated with traffic composed of cars, light goods vehicles and standard heavy goods vehicles (HGVs). A proportion of conventional articulated HGVs is then replaced by a smaller number of LHVs carrying the same total payload mass and volume. Four LHV configurations are investigated: an 18.75 m, 46 t longer semi-trailer (LST); 25.25 m, 50 t and 60 t B-doubles and a 34 m, 82 t A-double. Metrics for congestion, freight fleet energy consumption and car energy consumption are defined for comparing the scenarios. Finally, variation of take-up level and LHV engine power for the LST and A-double are investigated. It is concluded that: (a) LHVs should reduce congestion particularly in dense traffic, however, a low mean proportion of freight traffic on UK roads and low take-up levels will limit this effect to be almost negligible; (b) LHVs can significantly improve the energy efficiency of freight fleets, giving up to a 23% reduction in fleet energy consumption at high take-up levels; (c) the small reduction in congestion caused by LHVs could improve the fuel consumption of other road users by up to 3% in dense traffic, however in free-flowing traffic an opposite effect occurs due to higher vehicle speeds and aerodynamic losses; and (d) underpowered LHVs have potential to generate severe congestion, however current manufacturers' recommendations appear suitable.

Relationship between heavy vehicle speed limit and fleet fuel consumption on minor roads

“…Impact of raised HGV speed limit on traffic congestion. Figures 10 shows the congestion levels for both simulated traffic scenarios using the congestion metric C, defined in equation (11). The effects of speed limit on congestion are most apparent in the free-flow/ bound-flow transition region ($20 veh/lane.km), where drivers are restricted most by the slowest moving vehicles.…”

“…Greenshield's chart of vehicle flux vs. mean vehicle speed 3 ) were T and v 0 . Furthermore, as observed by Morrison et al,11 these variables have seemingly independent effects on the model. The study also considered varying the standard deviation of v 0 .…”

“…An extension to the IDM, known as the enhanced IDM model (ACC), is also available to safeguard realistic behaviour after 'cutin' manoeuvres. This enhanced model was used in a recent study by Morrison et al 11 to investigate the effects of heavy vehicle size on traffic congestion and fuel consumption.…”

Sustainability Intervention Mechanisms for Managing Road Freight Transport Externalities: A Systematic Literature Review

“…Our categorisation also highlighted some heterogeneity between modality and operations. For operations, routing and scheduling, facility planning, fleet design, and energy consumption were the most common topics within the European literature [30,36,71]. In contrast, the only paper from Africa that was reviewed under these categories explored a myriad of bottlenecks such as corruption, insecurity, and infrastructure limitations to road freight operations in Nigeria [24].…”