Speed-flow modeling of arterial roads in Singapore

Traffic volume and travel time data collected at a number of arterial roads in Singapore were used to analyze the speed-flow relationships for radial and ring arterial roads. A new travel time-density model was formulated by incorporating "minimum delay per intersection" and "frequency of intersections per kilometer" as model parameters. The appropriate values of these model parameters also were established. The adjusted R-2 value of this model was higher than those for the journey speed-density and running speed-density relationships. The free-flow speed and maximum flow values of the travel time-density model also fitted favorably well with field data compared with those of the journey-speed models. The radial road capacity estimates range from 835 passenger cars per hour per lane (pc/h/l) for segments with uncoordinated (unlinked) traffic signals to 905 pc/h/l for segments with proper signal (linked) coordination. Not much difference in estimated capacities is observed between linked and unlinked segments for ring roads. The capacity estimate for arterial roads is 890 pc/h/l.