Improved Operational Performance Assessment for Two-Lane Highway Facilities

Historically, two-lane highways served primarily as uninterrupted flow connectors between major population centers. Increasingly, however, population growth in areas between the major population centers along these highways is reaching levels such that occasional signalized intersections are commonly present. Given increasing congestion along these routes, particularly as a result of increased signalization, transportation engineers need methods and tools to analyze highway performance. The current analysis methodology contained in the commonly used highway capacity manual (HCM) for two-lane highways is limited in scope to completely uninterrupted-flow facilities. Furthermore, the spacing of signalized intersections along a two-lane highway is typically great enough such that the urban streets analysis methodology of the HCM is not applicable. Until recently, a simulation tool did not exist that could model the combination of two-lane highway segments and signalized intersections. This capability is now incorporated in the corridor simulation (CORSIM) microscopic traffic simulation program. This study uses the updated version of CORSIM to develop an analytical methodology for two-lane highway facilities (i.e., the combination of two-lane highway segments and signalized intersections). This study is a follow-up to a similar one conducted in 2009 at the University of Florida. However, a major distinction is that the previous study had to use a hybrid simulation approach [TWO-lane PASsing and CORridor SIMulation (TWOPAS and CORSIM)] whereas this study used the improved version of CORSIM that provides a unified and more accurate simulation approach. Although many similarities exist in the results for this study and the preceding one, several differences in model structures and coefficients were identified in this study. The service measure percent delay was retained for its efficacy in assessing operations on complex two-lane highway facilities (particularly those with signalized intersections), but this paper presents new percent delay-based level-of-service criteria thresholds. This paper also provides additional guidance for facility segmentation in situations in which a speed limit reduction is applied in the vicinity of a signalized intersection.