This paper gives a broad outline of recent advances in the design of unsignalised intersections in the UK, and refers to many additional papers providing more details. It reviews work in the following areas: (1) estimation of the capacity of major/ minor junctions and roundabouts; (2) levels of service, in terms of congestion, delays, and queues; (3) safety; (4) balance between different factors and issues, operational and economic appraisal, and computer aided design. The UK approach is strongly empirical, and it is based on the primacy of directly measured quantities (capacity, delay, accident rate) and on the importance of ensuring that models and relations correspond clearly to these quantities. The designer of an intersection has to achieve a difficult balance between many factors; it is important to guide that process to use computer programs and other automatic aids as much as possible, so that the designer can see quickly the key consequences of any trial design. Roundabouts have been used to good effect in the UK for many years; improvements since the introduction of the offside priority rule have led to particularly flexible principles for their design. When used appropriately, these improvements considerably improve the capacity and safety of roundabouts.
Abstract