Roundabouts are an important form of traffic control. It is now generally accepted that driver behaviour at roundabouts is one of `gap acceptance'. However, there are a number of assumptions about the interactions between drivers in different streams that have not been well established. Using data collected at a number of roundabouts in Melbourne, Canberra, Sydney and Brisbane, the movement of drivers was quantified and used to examine the assumptions applied in design guides for roundabouts, in particular the NAASRA guide. It is concluded that in general the exiting drivers have little effect on the behaviour of entering drivers at the same leg; that all circulating streams affect the entering drivers; that the entry lanes should be considered individually but with different behaviour; and that the behaviour of drivers change with increasing circulating flow. The behaviour of drivers at higher circulating flows is one of priority reversal or priority sharing. The likely delay and capacity under this form of control is compared with that obtained from an absolute priority control. It is concluded that priority reversal is recorded as decreased gap-acceptance parameters at higher flows (A).
Samenvatting