Although accepted almost worldwide as the definitive document to guide engineers in the design and operational analysis of highways, it could be argued that the Highway Capacity Manual (HCM) does not address two major issues: (i) the role of levels of service in strategy design, and (ii) the timing of investment based upon level-of-service criteria. In recent years, the United Kingdom Department of Transport has embarked upon a $10 billion motorway (freeway) widening program. This in turn has led the authors to develop a simplified level-of-service approach to guide the process of strategy design and the timing of investment. It is based upon three thresholds, termed capacity, congestion and design thresholds which define operating conditions at different flow levels. The breaking of the congestion and design thresholds define the need first, for additional capacity and second, the time period over which some flexibility can be exercised. As such, this approach addresses the two issues identified above. (A)
Abstract