Guidelines for the use of traffic control devices at stop-controlled intersections in the United States are provided in the Manual on Uniform Traffic Control Devices (MUTCD). Based on that, different dimensions of stop signs could be employed, even within the same jurisdiction. The study summarized in this paper investigated the effects of driver age and dimensions of stop signs on braking distance performance at stop-controlled intersections, while paying particular attention to older drivers. Data were collected at several stop-controlled intersections in non-residential areas in Hillsborough County, Florida, where three different sizes of stop signs (30", 36", and 48") were in use. Three driver age groups were also considered: older drivers, middle-age drivers, and young drivers. Statistical testing was used to find out whether the braking distances were different among driver age groups and also among different sizes of stop signs. Based on the observational data, it was found that older drivers had significantly longer braking distances for the largest size of the stop sign. Braking distances were also significantly different among the driver groups for the two larger sizes of the stop signs, but not for the smallest. In other words, older drivers see the larger sign and apply the brakes sooner resulting in longer braking distances. As such, the study recommends considering the replacement of smaller sizes of stop signs with the largest size in non-residential areas with a high older-driver population to increase safety at stop-controlled intersections.
