The impetus for the introduction of the earliest traffic signals was to ensure safety at intersections by keeping conflicting traffic streams apart. As well as increasing safety, the introduction of traffic signals also increased delay to vehicles; and there has subsequently been much research into ways of minimising unnecessary delay whilst preserving safety, leading to the development of many different methods of traffic signal control. Traditionally, the main performance measure for judging the efficacy of a new traffic signal control system, whether for an isolated intersection or fora network, has been the reduction of vehicular delay and stops. Other considerations such as convenience and safety for pedestrians or bus priority have usually been incorporated into the systems later in their development as pragmatic features required for on-street operation, but have not been used as performance measures during the development and optimisation phases. This may be partly due because of the difficulty of modelling pedestrian behaviour or bus priority strategies, but is also due to the underlying assumption that the most important road-users are the vehicles (and their drivers!)
展开▼
