Examining lateral positions of cars and heavy vehicles on a two lane, two way motorway

Abstract

While most motorways in Queensland are divided with at least two lanes in each direction, a few motorways have been constructed as two lane, two way roads. These "half motorways" have been designed and constructed with the intent of eventual duplication to divided carriageways. This type of roadway is similar to a two lane, two way highway constructed to a high standard. Motorways are critical elements of urban freight networks. There is a growing need from the freight industry to allow multi-combination vehicles to use a larger network of urban roads. This raises concerns regarding the psychological impacts on drivers of surrounding vehicles, and their behaviour around the MCVs.

Lennie and Bunker (2004) studied some behavioural characteristics of passenger car drivers surrounding MCVs on a four lane, divided motorway. However, drivers are expected to behave differently while opposing each other on an undivided two lane, two way motorway or highway. That study was extended here to examine driver behaviour on the Port of Brisbane Motorway, which is a "half motorway". Specifically, the following were examined: Lateral position distribution for passenger cars, semi-trailers and B-doubles (23m or longer); and lateral separation distribution of passenger cars from heavy vehicles and other passenger cars.

The study showed that a maximum 7s time gap between opposing vehicles influenced drivers’ positioning of their vehicles. It was shown that the lateral positions of cars, utility vehicles, and semi-trailers are statistically different when opposed than when unopposed; whereas, the lateral positions of B-doubles were not. This indicates that B-double drivers did not tend to move laterally when opposed by oncoming traffic.

On average, passenger car drivers did not position their vehicles appreciably differently when opposed by semi-trailers and B-doubles than other passenger cars, and there was no appreciable difference in passenger car drivers’ positions when faced by oncoming semi-trailers than B-doubles.

Average and 95th percentile envelopes were provided to indicate position in the lane of unopposed and opposed vehicles on this type of roadway section. The off-side edge of the 95th percentile passenger car straddled the edge line, while both the 95th percentile semi-trailer and B-double occupied part of the wide, sealed shoulder. The semi-trailer wandered further onto the shoulder. The vehicle envelopes are useful to understand the impacts of heavy vehicles on driver behaviour, and can also inform road design and pavement asset management.