Travel speeds on two-lane main roads. The use of data on road safety work

The Finnish Transport Agency monitors travel times in real time on the busiest roads. The aim of this work was to test the compatibility of collected travel time data with travel speed and passing frequency research, particularly from the perspective of information needs in road safety work. The project examined the 2010 travel speeds of 66 road links on two-lane main roads, the length of a link being 30 km on average. Bypass frequency was studied on seven links. Travel-time monitoring data are very suitable for speed studies, as long as clear outliers are excluded. Travel speeds calculated from the data are roughly equal to average point speeds on main roads. Travel speeds are useful for identifying road sections where speeding is common. The summer season travel speed in 2010 was on average 90.6 km/h, and the winter season travel speed 85.5 km/h on the studied two-lane main road links. Travel speed in summer was most commonly about 2 km/h lower than the speed limit. During the winter season travel speed exceeded the speed limit on roads with 80 km/h winter speed limit, and was below the speed limit on roads with higher speed limits. In addition to the speed limit, travel speed correlated with traffic volume, type of road, roadside settlements and automatic speed control. Travel time monitoring data are suitable for passing rate studies only when the monitoring system registers a vast majority of cars on the road. Even then, observed passing rates seem to be significantly smaller than in previous studies. Thus, the passing rates calculated with travel-time monitoring data are comparable only with each other.