Incorporating Highway Safety into Level of Service

The Highway Capacity Manual is used extensively for highway design and highway evaluation purposes; it relies upon the relationship between travel speed and the volume/capacity ratio for an expression of the level or quality of traffic service. A need exists to include more consideration of highway safety within the concept of level of service, and an examination of the concept of probability of danger of collision has been conducted. This approach takes into account various values of the probability of danger of collision and provides a means of introducing a third major parameter into level of service determination. The results indicate that, for the single-lane, car-following situation, the current levels of service are not completely adequate for safety considerations.