Gray Areas in Isolated Intersection Control-Type Selection: Complementary Decision-Support Tool

The intersection control-type selections for future facilities can be determined by comparison of a common measure of effectiveness that is average control delay. However, rigid comparisons of such measures tend to mislead the decision-making process in practice, since there must be latent factors in quantification. To this end, this paper proposes the performance comparison framework of different transportation facility alternatives using a common quantitative measure. By considering the uncertainties in a quantification process, the proposed framework provides gray areas (i.e., intuitively visualized information, which decision-makers can use to assist in their engineering decisions). The average control delay of two-way stop control, all-way stop control, signal control types, and roundabouts were compared with contour lines of delay differences. It is found that the delay of a roundabout increases rapidly as the traffic demand increases. Hence, a signal control type has the minimum delay level in that case, despite the fact that the roundabout outperforms for most of the low-demand conditions. When the signal timing plan is optimized, this feature becomes evident. With consideration of the margin of error in the delay, a gray area on the minimum delay surface between the signal control and roundabout types enlarges in the low-demand area. The gray areas can be utilized by practitioners to decide the best intersection control type with consideration of construction and maintenance costs over delay reduction benefit.