Motorist Speed Change Behavior at Flashing Signal Operations During Late Nights

Motorist speed change behaviors at flashing yellow signal operations during late nights were evaluated by comparing upstream and downstream spot speeds. On a 1900-foot long four-lane arterial street with low traffic volume, about 110 vehicles per hour eastbound and westbound, directional analysis of aggregated spot speeds on the major street, Chain Bridge Road, shows a significant speed increase of 5.5 miles per hour eastbound and a significant speed reduction of 4.4 miles per hour westbound. A simple linear regression analysis shows a strong relationship between speed difference and ratios of upstream to downstream traffic volumes. That is, for a given traffic volume condition, a speed increase of about 5 miles per hour occurs if the downstream volume is half of the upstream volume, and a decrease of about 4.7 miles per hour occurs if the downstream volume is about double the upstream volume. The study suggests that vehicles entering or exiting minor streets is a contributing factor that affects approach speed of motorists on the major street, rather than the flashing yellow indication itself. Agencies considering flashing signals during late nights should review additional locally specific requirements that determine motorist traffic behaviors, including nearby significant traffic attractions or generators such as late night businesses or major freeway interchanges.