Speed and Delay on Signalized Arterials

This research presents a model to predict the influence of demand and capacity on the running speed of signalized arterials in Montgomery County, Maryland. The model separates the changes to link running speed due to same-direction traffic and intersection approach delay from cross traffic. It is found that flow has a small impact on link speed, each 1000 vehicles per lane per hour reduces speed by 4 - 8 kph. Longer links have higher speeds, indicating that they more closely approximate free-flow conditions. A surprising result comes from measuring the effect of an additional lane on link speed, after controlling for flow per lane. It is found that there are slight diseconomies of additional lanes in terms of speed, each additional lane is associated with somewhat slower speeds. Measures of intersection and link travel times are also compared. Although link running times exceed intersection stopped delay, total intersection delay (stopped and approach) exceeds the delay caused by same-direction traffic. This information can inform investment decisions about roadway and intersection improvements.