Operating speeds for incremental and leapfrog investment strategies in bus-based transit

This study compares the leapfrog and incremental approaches taken to improve public transport with an intention of achieving a complete bus rapid transit (BRT) system as the final product. The leapfrog approach is characterised with corridor level uplift following the full specification of Latin American BRTs to replace the existing minibus taxis (MBTs) as evidenced in Cape Town, Johannesburg and Tshwane. The incremental approach was envisaged to involve three interventions starting with scheduling of the existing MBTs, operating scheduled buses in mixed traffic and final introduction of BRT dedicated lanes with median stations. Rustenburg Local Municipality has taken an incremental approach in which the existing MBTs have been scheduled and buses added to enhance capacity on certain routes. This comparison of the two strategies is based on travel time savings as the benefit accrued from the interventions.

The study relies on empirical measurements of actual public transport operations to develop models of operating speed for the interventions. Rustenburg Rapid Transit and Tshwane BRT are used as case studies. Ordinary Least Squares (OLS) models were calibrated and tested for conformity with OLS assumptions. Weighted least squares (WLS) was used to correct for heteroskedasticity while generalised least squares (GLS) was used to correct for both heteroskedasticity and serial corelation. The calibrated models were based on operating speed as the response variable while unsignalised intersections per kilometre, signalised intersections per kilometre, stations (stops) per kilometre and land use were predictor variables.

To illustrate their application, the developed models were applied to a theoretical 10 km corridor to estimate the operating speed and travel time under various interventions. Travel time was adjusted to account for variations in traffic congestion and passenger demand. Travel time savings were calculated as the difference between travel times for scenarios under consideration and the base scenario (no intervention). Results indicated that both incremental and leapfrog approaches provided positive time savings. The leapfrog approach provided maximum time savings under high demand and traffic congestion. All steps involved in the incremental approach provided a positive time saving. It is concluded that smaller cities and municipalities can follow an incremental approach while bigger cities can leapfrog to complete BRT.