LEVEL OF SERVICE OF TWO-LANE RURAL HIGHWAYS WITH LOW DESIGN SPEEDS

The parameters and approach to the evaluation of levels of service for two-lane highways were changed substantially from the 1965 Highway Capacity Manual (HCM) to the 1985 HCM. A principal change was the introduction of percentage time delay as a parameter used to describe service quality. Another significant change was the elimination of an explicit and fully defined methodology to analyze two-lane highways with design speeds lower than 96 km/hr (60 mph). Although the 1985 HCM can be applied to highways with low design speeds, the procedure is acknowledged to be incomplete, at least as far as speed is concerned. Alternative methods are proposed to analyze the level of service for two-lane highways with design speeds of 80 km/hr (50 mph); the methods are based on relationships among speed, volume, density, and percentage time delay. The relationships were developed with the aid of the TWOPAS computer model, which is the same model used for the development of the basic relationships used in the HCM. In conclusion, a strategy for future development is proposed.