The roundabout has great advantages compared to normal intersections. It's safer and has a higher capacity. In places where the capacity of roundabouts isn't sufficient to cope with the occurring traffic, city councils are thinking about placing roundabouts consisting of two lanes. Problems regarding these roundabouts are the big use of space, the unsafe weaving areas and the low capacity of two lane roundabouts in comparison to normal roundabouts. The goal of this study was to develop alternatives for the roundabouts consisting of two lanes on account of a literature study after which they were evaluated on the basis of some criterions. The one-lane roundabout is used as a reference alternative. The criterions on which the alternatives were evaluated are traffic safety, crossing of cyclists and pedestrians, capacity and use of space. A conclusion drawn from the evaluation of traffic safety is that the two lanes roundabout is unsafer than the normal roundabouts. The cause is the necessity of weaving on two-lane roundabouts and the relative high speeds, because of the big dimensions. With regard to pedestrians and cyclists there aren't many differences between the alternatives. If the alternatives are compared to the one-lane roundabout or an intersection with traffic signals the variants are much harder to pass for pedestrians and cyclists, because they have to make a detour. Capacity calculations are based on the Swiss method of Bovy. For every variant is calculated within what limits the capacity is. The capacity of a two-lane roundabout seems the best at first sight. This equals 3550 veh/h when we assume a comparable origins-destinations matrix, while the capacity of a one-lane roundabout equals 2345 veh/h. If we assume that only the left going traffic will use the left entrance the capacity of the two-lane roundabout equals 3375 veh/h. If the one-lane roundabout is extended with a bypass for the right going traffic the capacity increases to 3015 veh/h. Especially when there is a big flow of the right going traffic this variant is very useful. It appears that the capacity of the variants is only a factor 1,1 to 1,5 greater than the normal one-stroke roundabout. The capacity of a priority intersection equals 1560 veh/h. There isn't much difference in the use of space between the variants. The difference between the use of space of these variants and the one-lane roundabout is much bigger. There is a factor between 1,5 and 3,0. It appears that the construction of a two-lane roundabout is not advisable especially in city centres unless there is a combination with traffic lights. The one-lane roundabout is a safer solution with a fair capacity. Special attention must be paid to the way in which crossing for cyclists is organized. (A)
Samenvatting