S12 Main road improvement solutions. Wide-lane road in winter. Follow-up study on route 6 between Koskenkyla and Kouvola

A 54-kilometer section of wide-lane road was completed on route 6 between Koskenkyla and Kouvola at the end of 2004. The lanes are 5.5 m wide, which is clearly wider than normal (3.5 or 3.75 m). The purpose of a wide-line road is to smooth the flow of traffic, increase overtaking possibilities and improve road safety. This study assessed whether these objectives were realized in winter conditions. A wide-lane road is usually plowed with a snowplow equipped with a side plow, but if necessary, two snowplows may be used during heavy snow. Since the roadway is about 50% wider, the amount of salt needed for antiskid treatment increased around 40% -50% compared to the previous situation. There was no increase in the frequency of salting or the amount of salt used per square meter. Based on performance monitoring of the 2004-2005 winter season, the labor costs of winter maintenance of a wide-lane road were about 2,400 Euros/km/winter. These labor costs do not include overhead costs or other fixed expenses of the maintenance contract, so they do not represent the total cost of winter maintenance. The winter maintenance costs of the wide-lane road were slightly lower than the 2,600 Euros/km/winter costs of a wide-shoulder road used as a reference, which is due to the slightly lower performance quantities. Depending on the conditions, the minimum friction coefficient required on a winter maintenance class Is road is 0.25-0.30. Most of the time there were non-skidding winter driving conditions on the road, as measurements made in the middle of the lane indicated that 15% of the observations were below the limit for non-skidding winter driving conditions (friction coefficient <0.30) and 6% were below the limit for good winter driving conditions (friction coefficient <0.25). When driving on or near the centerline, the friction coefficients were slightly worse than in the middle of the lane, as 22% of the observations were below the limit for non-skidding winter driving conditions (friction coefficient <0.30) and 10% were below the limit for good winter driving conditions (friction coefficient <0.25). Based on systematic digital image monitoring, the road was bare most of the time (approx. 70%). Strips of loose or packed snow that hindered driving and overtaking accumulated only when it snowed. Road markings were difficult to see because of snow on mid-line 20-30 % of the wintertime. Driving conditions clearly affect driving speeds. The average speed of traffic on the wide-lane road with a 100 km/h speed limit dropped 11 km/h when the friction coefficient decreased by 0.1. In winter, 29% of the vehicles on the widelane road exceeded the 100 km/h speed limit, while the corresponding figure on two-lane main roads is 18%, on average. However, the 4% that exceeded the speed limit by over 10 km/h corresponded to the average. The need for speed limits that vary according to driving conditions was assessed on the basis of road weather station data. According to the criteria used by the Kaakkois-Suomi region on motorways, as far as weather and driving conditions are concerned, the winter speed limit could be 100 km/h most of the time (85-87 %). Lowering the speed limit to 80 km/h is necessary 13-14 % of the time. A 60 km/h speed limit is rarely necessary (0.04-0.11% of the time). There were 17 traffic accidents on the section of road during the six-month period following its completion. Seven were single-vehicle accidents, three were moose or deer accidents, three were junction collisions, three were head-on collisions and one was an overtaking collision. The material is not sufficient for reliable analysis, but based on the accidents that occurred during the first winter, there appear to be no particular problems resulting from the type of road. This report may be found at http://alk.tiehallinto.fi/julkaisut/pdf/3200959-vleveakaistatie_talvella.pdf