Due to the number of motorway construction sites with only a single-lane layout (in each direction) still required in the new German Länder, recommendations are to be drawn up for determining the arrangement of the sites, with a view to improving the traffic flow and reducing the risk of accidents, while taking the particular road conditions into account. To this end, traffic and accident studies were carried out on a total of 9 single-lane construction sites with 2+0, 2+1 and l +1 layouts, i.e. on a total of 17 construction sites with through-traffic, with zones of varying length and with varying roadside furniture elements. To analyse the traffic flow, a floating car equipped with instrumentation carried out traffic progress measurements, following traffic through the construction sites; local traffic density, speed and time intervals in the construction site bottlenecks were also measured. Accident studies were carried out on the longer-term construction sites. At practically all of the construction sites, a very high level of speed was recorded; the permissible speed limits were clearly exceeded in all zones. Speeds recorded for passenger vehicles and heavy goods vehicles were generally similar. In some instances, average speeds for HGVs in the bottleneck areas were actually higher. In the construction site bottlenecks, capacity values amounted to around 1,300 vehicles/hr in each direction, even with a high percentage of goods vehicles of 20 to 30%; on a stretch with a high percentage of local drivers, values were even cited up to 1,400 vehicles/hr in each direction with the percentage of goods vehicles at 30%, indicating higher values than previously shown. Single-lane construction sites can therefore be introduced on road stretches with DTV values up to roughly 30,000 vehicles/24hr (in both directions) without reducing the traffic flow to any great extent. Similar to previous investigations, a clear increase was shown in the risk of accidents due to the single-lane construction sites as compared with the free stretches. Divided according to the individual areas, by far the highest accident rate was recorded for areas in which the road narrows down, followed by crossover points. These areas should therefore be equipped with flashing lights and guide rails to increase awareness. To reduce the occurrence of accidents involving oncoming traffic, skid rails or crash barriers are recommended for dividing the two lanes of traffic in the inner zones, which were also shown to have the effect of reducing the speed slightly. The speed limit can be uniformly raised to 80km/h for the entire construction site thoroughfare, with the exception of narrow sections and access points within the construction site areas. (A)
Samenvatting