Traffic Flow Characteristics of Isolated Off-ramps in Iranian Expressways


Civil Engineering, Sharif University of Technology


The purpose of this study was to investigate traffic flow characteristics at off-ramp junctions in Iranian expressways. The study was conducted on the traffic behavior in isolated off-ramp vicinity of 6-lane expressways. The database consisted of traffic flow and traffic speed information extracted from videotapes. The relationship between diverging traffic flow in the right lane of expressway with total expressway and ramp flows was investigated. The 1985 U.S. Highway Capacity Manual, the 1985 HCM, models, and numerical values for isolated off-ramp analysis were evaluated and modifications for Iranian expressway system were suggested. The speed -flow relationship study showed that for a developing country such as Iran, the developed country's transportation engineering and planning manuals such as the 1985 HCM could give misleading results. Highway capacity analysis should be adjusted for a developing country's prevailing traffic composition and driver behavior.