Assessment of Design Hours for Freeways

Conventional methods for the assessment of the level of service on freeways are based on the analysis of one specific peak hour. In Germany, as in many other countries, the 30th hour is defined as the design hour; in other words, the 30th highest hourly traffic demand that arises in 1 year is used as the input value for freeway design. This paper analyzes the impact of different design hours on the level-of-service assessment of basic freeway segments. On the basis of traffic data from 50 freeway sections in Germany, the extent of congestion over a whole year is estimated through the application of a macroscopic simulation model. With the model, all travel time losses attributable to congestion can be related to the hours in which the congestion was caused. It is found that on freeways with mainly recreational traffic, most time losses are caused within the first 30 h; in comparison, on freeways with mainly commuter traffic, considerable time losses occur even beyond the 100th hour. Therefore, the choice of a specific design hour between the 30th and the 100th hours does not significantly affect the assessment results.