Passenger car units of vehicles on Singapore expressways

Abstract

Passenger Car Units (PCU) for vehicles on expressways in Singapore was developed for level of service LOS D and LOS E when the posted speed limit was 80 km/h. The posted speed limits for most expressway segments in Singapore have now been raised to 90 km/h, and the vehicle speed limits for goods vehicles have also been raised. In order to determine whether the current PCU values are still valid, data would be extracted from recorded tapes and multiple linear regression method would be selected to establish PCU values.

In this study, service flow rate for LOS D would be 2136 based on the volume to car ratio of 0.89 in the HCM. LOS D was determined by corresponding flow rate of 15mins with the service flow rate of 2136. Any lane which has service flow rates that are close to 2136 will be deemed as LOS D. From there, platoons of vehicles are determined. Multiple linear regressions are then performed using Microsoft Office Excel, and the coefficients can be obtained. In order to calculate the PCU value of a particular vehicle, its coefficient is divided by the coefficient of the passenger car.

Longer and slower vehicles imposed a greater effect on the traffic as drivers tend to slow down or keep a further stopping distance from them. The increase in flow rate therefore raises the rate of impedance which reduces PCU values. PCU values are smaller than before due to the raise in speed limits. Nowadays, drivers are more aggressive in road driving as they tend to speed up more often and they keep shorter safe distance. The fact that the raise in speed limits with driver’s behaviour could impose an impact on the PCU values.