Abstract
A divided two-way two-lane (TWTL) expressway crosssection was defined in the most recent update of Road Structure Ordinance in 2003. This novel structure is expected to contribute to saving building cost of rural expressways particularly with low traffic demands. However, since its speed performance is remained unclear, the expected target speed may not be realized under some road traffic conditions.
This paper therefore aims to analyze impacts of various conditions on speed-flow relationships of the divided TWTL expressway sections by using vehicle detector data, towards implementing the performance-oriented planning and design policy. After extensive analyses on several influencing factors that affect speed performance such as heavy vehicle ratio and precipitation, speed-flow relationships under different conditions are finally formulated. By using the proposed formulae, speed performance of the TWTL expressway sections can be verified at the planning and design stage of highways.
