Bus Priority on Roads Carrying Heterogeneous Traffic: a Study using Computer Simulation

Arasan, Venkatachalam Thamizh; Vedagiri, Perumal · 2008 · Crossref

DOI: 10.18757/ejtir.2008.8.1.3329

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Summary

This study addresses the challenge of improving public transport efficiency in Indian cities, where traffic is highly heterogeneous and lacks lane discipline. The authors aim to determine the impact of introducing exclusive bus lanes on urban arterials, specifically assessing how such priority measures affect the speed and level of service (LOS) of other motor vehicles. The research is motivated by the need to enhance bus attractiveness and reduce congestion without expensive infrastructure expansion, while acknowledging that existing simulation models are designed for homogeneous traffic and are unsuitable for Indian conditions. The researchers utilized a dynamic, stochastic discrete-event simulation model named HETEROSIM, which represents vehicles as rectangular blocks moving on a shared road space without fixed lanes. The model was calibrated and validated using field data collected via video recording on a six-lane bridge in Chennai, India. Data collection involved analyzing traffic composition, vehicle dimensions, free speeds, and headway distributions. Statistical tests confirmed that vehicle arrivals followed a Poisson distribution and headways followed a negative exponential distribution. Validation involved comparing simulated mean speeds against observed field speeds for eight vehicle categories (including buses, trucks, cars, two-wheelers, and bicycles); a paired t-test showed no significant difference between simulated and observed speeds at a 95% confidence level. For the experimental application, the model simulated an 11-meter wide urban arterial with a representative Chennai traffic composition. The study compared traffic flow under two scenarios: mixed traffic without a bus lane and traffic with a 3.5-meter exclusive bus lane adjacent to the median. Simulations were run across a wide range of traffic volumes. In the baseline scenario (no bus lane), the road capacity was determined to be approximately 6,900 vehicles per hour, with a Level of Service C corresponding to a volume of 4,800 vehicles per hour. When the exclusive bus lane was introduced, the available road space for other vehicles was reduced. The results indicated that the introduction of the bus lane significantly reduced the speeds of non-bus vehicles due to the constrained road width. The primary finding establishes that under highly heterogeneous traffic conditions, providing an exclusive bus lane limits the maximum permissible volume-to-capacity ratio for the remaining traffic stream. To maintain a Level of Service C for all motor vehicles except buses, the volume-to-capacity ratio must not exceed 0.53. This implies that while bus lanes improve bus performance, they impose a stricter capacity constraint on the general traffic stream in heterogeneous environments compared to homogeneous traffic standards. The study concludes that careful assessment of traffic volumes is necessary before implementing bus lanes to avoid severe degradation of service for other road users.

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• traffic density