In 2001 the Finnish Road Administration decided to prohibit overtaking using the passing lane in the direction with the single lane on rural two-lane roads for safety reasons. Before this change in road markings double barrier lines (marked islands) were used only in the end of a passing lane providing that sight distances or other conditions did not require longer no-overtaking zones in the direction with the single lane. In this before-and-after study changes in the traffic flow characteristics were studied at three different locations on main road 1 and main road 2 in Southern Finland. Two locations had a pair of passing lanes, one in each direction, and one location had only one passing lane. The field studies consisted of point measurements using double induction loops, video measurements, and measurements using an instrumented moving observation car. All the passing lanes were upgrade and the speed limit was 100 km/h. After the change in road markings the space mean speeds of vehicles driving in the single lane direction has decreased clearly only at one location. The decrease is 1-3 km/h (1-4 %) at one-way flow rates from 100 to 1200 veh/h. Two other locations also showed a statistically significant decrease in speeds, the decrease being only 1 km/h at the most. At the other location the speed change is twofold: at one-way flow rates below 550 veh/h the space mean speed has decreased and at flow rates at 550-1300 veh/h the mean speed has increased. The standard deviation of the speed distribution showed small changes only at two locations. The share of vehicles driving in platoons (platoon criterion 3 sec.) has increased slightly at all locations except one. The smaller the flow rate is the higher is the increase in platoon percentage. The biggest change was from 20 % to 25 % at flow rates of 100 veh/h and from 53 % to 55 % at flow rates of 500 veh/h. At flow rates of 1000 veh/h the change is only 0.5 %-units. Overtakings are still made in the single lane direction using the opposing passing lane, although it is prohibited. However, the number of overtakings and the overtaking rate in the single lane direction have decreased by 83-96 % after the changing of the road markings. At the locations with a pair of passing lanes the overtakings moved to the passing lane downstream of the no-overtaking zone. This improves traffic safety providing that the downstream passing lanes are long enough. In the future, attention should be paid to sufficient lengths of the passing lanes, especially at road sections where the change in road markings has significantly decreased overtaking possibilities. After the change in road markings the overtaking manoeuvres take place in traffic situations that are safer than before: the share of situations classified as potentially dangerous (situations where an overtaking was performed despite the fact that a vehicle planning to overtake could have been hidden behind oncoming big vehicles or platoons) has decreased from 8 % to 2 % according to the moving car measurements and from 14 % to 6 % according to the video measurements. The double barrier lines probably have awoken the drivers to notice that overtaking at these locations might be dangerous. In process of time drivers' obedience to the law might also become better, when they are no longer overtaking from from old time,
Samenvatting