Roundabouts and heavy vehicles.

Roundabouts have become a subject of great interest in the 1990s. Modern roundabouts differ from traditional traffic circles in that they force the vehicles to slow down. The behaviour of heavy vehicles in traffic is different compared to light vehicles because of their size and operation. Many large commercial vehicles are unable to negotiate small radius turns.Problems experienced at roundabouts by drivers of heavy vehicles include insufficient vehicle path curvature, high and sharp-edged kerbing on the truck apron etc. The main aim of this study was to recognise problems and investigate solutions to the problems of heavy vehicles at the roundabouts. Data was collected in both winter and summer on 10 roundabouts chosen from the Finnish main road network. Data collection included recording vehicle speeds, recording vehicle paths, recording geometric parameters and video recording of each individual vehicle. Statistical analyses have been carried out to compare the recorded vehicle data with the geometric parameters. Vehicle path and speed analyses were performed and considered against the straight path through the selected roundabouts. Significantly vehicle paths differed between summer and winter at most of the roundabouts, being generally closer to the kerb of the central island in winter than in summer. The path taken by the vehicle depends on radius of the curvature and the width of the circulatory carriageway. The smaller the curvature and width of the circulatory carriageway, the closer the vehicle path is to the central island. According to the observations of the roundabouts studied, a radius of curvature below 35 meters can cause difficulties for truck and trailer combinations. The most serious difficulties are experienced by drivers of module combinations and other track and trailer combinations, whereas drivers of buses and trucks without trailers have fewer problems. For bus drivers, the behaviour of other drivers at roundabouts seems to be the most serious problem, while for trucks without trailers the biggest problem is the slippery road surface in winter. Design aspects, such as kerbs and restricted carriageway width are some of the biggest problems for drivers of module combinations and other truck and trailer combinations. Hitting kerbs can result in punctured tyres. Most drivers seem to prefer roundabouts to signal-controlled junctions. Those with the opposite view also have a more negative attitude towards roundabouts in general. However, as drivers acquire more experience, their attitudes towards roundabouts tend to become slightly more positive.