Effectiveness of Grips in alleviating traffic congestion

Graphic route information panels (Grips) provide traffic information by displaying a few distinct colours on simple network topologies. The images that the Grip are able to present are usually limited, as are their corresponding splitting rates. Assessing the effectiveness of these limited splitting rates in alleviating traffic congestion is of practical significance. To this end, this paper considers the simple but typical Grip that presents three colours on a network with two routes. An optimal iterative guidance strategy is taken as the strategy for selecting splitting rates. All possible splitting rates that the Grip can deliver are enumerated in deterministic and stochastic simulation scenarios, in which drivers completely follow route guidance and subsequently choose a route based on a probability. The results are analysed and compared, and further general conclusions are made. A number of investigations are addressed including a basic requirement for the Grip's capacity to alleviate congestion, stability of the traffic influenced by the guidance information, impact of the uncertainty of drivers' understanding of the information, and so on. The results are useful in the assessment and proposal of practical route guidance strategies as well as when educating drivers to understand better the guidance information provided by the Grip.