Improving a Model for Speed / Density Relationship on Arterial Roads in Baghdad City


This paper was undertaken to investigate the relationships between speedand density on urban arterial roads of Baghdad City. This research work was basedon the traffic survey data (PC volume and average speed) collected in PalestineStreet in 3 sections at two directions through 12 hours within 3 weekdays. Thedensity is computed using fundamental formula of traffic flow. Eight theoreticalSpeed-Density models (5 are single Regime Models and 3 are Multi-Regimemodels) are validated by the field data by two statistical test methods (CHISQ testand Paired T-test). The results show that no one of the theoretical models is goodin fit with the real data. Then a Multi-Regime Model is improved under two rangesof density (<70 and >70) at south approach and (<60 and >60) at north appraoch .This model is tested using regression analysis, CHISQ test, and Paired T-test. Thisanalysis shows that the model has good fit with the field data.