This report presents two studies on the functionality of a section of narrow four lane road with a center guard rail on main road 5 between Vehmasmaki and Hiltulanlahti. In the first study, drivers were interviewed and questionnaires were distributed in the vicinity of the experimental road section during the summer and autumn of 2001 with the intention of mapping opinions about the road type. The second study examined the cross-directional position in the traffic lane of overtaking passenger cars and small and large vehicles being overtaken during the overtaking situation on both a narrow four-lane road and a wide motorway in summer and winter conditions. The study was implemented by videotaping overtaking situations while driving behind vehicles being overtaken and then performing computer-assisted analyses of the videotaped situations. The measurements were made in May - June 2001 and January 2002. The studied sections of road were the narrow four-lane road on main road 5 between Vehmasmaki and Hiltulanlahti and a section of motorway between Hiltulanlahti and Kettulanlahti as well as a section of motorway on main road 7 between Ring III and Skoldvik. Drivers interviewed in the summer of 2001 felt the condition of the road surface was a major hindrance that greatly affected their evaluation. Because the road section was constructed in winter, it suffered from settlement in several places, which were repaired the following autumn in conjunction with repaving. In interviews conducted after the repair work was done, the narrow four-lane road was given nearly as high grades as a motorway of normal width (8.55 vs. 8.71). In the respondents' evaluations, the positive factors of the narrow four-lane road type were sufficient lane width, smooth traffic and a suitable speed limit. A negative factor was drifting of snow alongside the road, which made overtaking difficult. The good and bad factors of the road are presented in more detail in the report. The study that assessed driving behavior indicated that the position in the right lane of a vehicle being overtaken on a narrow four-lane road and a motorway depends on the type of vehicle in question. The left side of trucks and heavy trailer-towing vehicles was closer to the left edge of the lane (the lane divider line) than that of passenger cars, which is partly due to the greater width of the heavy vehicles. However, the distance of different vehicle types in the right lane from the left edge of the lane (the lane divider line) was of the same magnitude on both road types. There were no significant differences in the driving lines of vehicles in the right lane in winter and summer conditions. The driving lines of vehicles being overtaken on a narrow four-lane road moved a little further from the lane divider line in winter than in summer, but on a motorway the effect of winter conditions was mainly apparent as a greater spreading of driving lines. A comparison of driving lines of overtaking cars in summer and winter showed that the distance of the overtaking vehicle from the left edge of the overtaking lane on a narrow four-lane road was 50-90 cm in summer and 90-180 in winter. Thus, the driving lines of overtaking vehicles moved about 50-100 cm further from the center divider in winter. The corresponding distances on a motorway were 30-60 cm in summer and 10-110 in winter. So, driving lines on a motorway did not clearly move further from the center divider, but rather the driving lines spread out more. Therefore, it was concluded that overtaking drivers on a narrow four-lane road select driving lines that are about 10-30 cm further from the left edge marker line and center divider in summer conditions and about 65-100 cm further in winter conditions than on a motorway. In winter conditions the driving lines of overtaking vehicles on both road types are spread out more than in summer conditions. Drivers in overtaking situations on a narrow four-lane road accept 20-50 cm shorter distances to the vehicles being overtaken in summer and about 70 cm shorter distances in winter than on a motorway. Apparently, on a motorway overtaking drivers can maintain desired overtaking distances regardless of the time of year. Drivers on a narrow four-lane road in winter conditions prefer to drive further from the center divider and guard rail, meaning they have to shorten the distance to the vehicle being overtaken. However, drivers on a narrow four-lane road in summer conditions "watch out" more for the vehicle being overtaken than the center guard rail.
Samenvatting