Speeds on a three-lane road section with median barrier and vehicle distances from median barrier on main road 54 in Finland

The Finnish Road Administration aims to equip all new and part of the old passing lanes with a median barrier. With a median barrier it is possible to prevent head-on collisions, which are the most serious accident type on main roads. In Finland the first three-lane road section with a median barrier was opened in October 2002 on main road 54 in Loppi. The passing lane is in the westbound direction towards Loppi center. In this research work spot speeds and platooning in different weather and road conditions on the three-lane road section and on a two-lane road section nearby were investigated. Data were gathered from the end of May 2003 to the beginning of May 2004 using traffic analyzers with double induction loops. In addition the position of the vehicles on the lanes next to the median barrier were measured in two locations using a distance measuring device (LAVEG). The ADT of main road 54 in Loppi was about 6,000 veh/day in 2003. In the summer time the speed limit is 100 km/h and in the winter time 80km/h. During the measurements the flow rates were mainly below 500 veh/h in the summer time and below 400 veh/h in the winter time. The share of vehicles using the passing lane was 5-10% in daytime traffic and 2-5% in night-time traffic. The mean speed in the three-lane cross-section was, depending on time of day and weather and road conditions, in the summer time in the westbound direction towards Loppi 87-95km/h on the basic lane, 97-110km/h on the passing lane, and 88-93km/h in the one lane eastbound direction. In the winter time the mean speeds towards Loppi were 77-88km/h on the basic lane, 87-100km/h on the passing lane (except during snowfalls in the night), and 81-90km/h in the one lane eastbound direction. During snowfalls in night time traffic the mean speeds on the passing lane were 63-81km/h. However, the number of vehicles on the passing lane was very small in the night, and the speeds of the maintenance vehicles probably affected the mean speeds more than on other lanes. In the one lane eastbound direction the mean speed was usually higher in the three-lane cross section with median barrier than in the two-lane cross-section without median barrier. The speed difference was 1-3km/h (1-4%). Only in rainy conditions or during snowfalls in the night the mean speed was 1-2km/h (1-2%) lower in the two-lane than in the three-lane cross-section, or there was no difference at all. In the westbound direction, towards Loppi, the mean speed on the basic lane in the three-lane cross-section in daytime traffic and in good road and weather conditions was on the same level or 1km/h (1%) higher than in the two-lane cross-section. In daytime traffic in rainy conditions or during snowfalls and in night-time traffic regardless of road conditions the mean speeds on the basic lane were 1-6km/h (1-7%) lower in the three-lane than in the two-lane cross-section. On the passing lane, instead, the mean speeds were almost in all weather and road conditions higher than in the two-lane cross-section in the westbound direction. The difference was 4-14km/h (4-15%). Only in night-time traffic during snowfalls the speed on the passing lane were 4-20km/h (5-24%) lower than in the two-lane cross-section. In the two-lane cross-section road lighting makes driving easier in the dark. In the three-lane cross-section there is no road lighting. As expected, the drivers on the passing lane drove closer to the median barrier when overtaking a heavy vehicle than when overtaking a light vehicle. This report may be found at http://alk.tiehallinto.fi/julkaisut/pdf/3200916-vnop_ohitkaistkohd_ja_ajo.pdf