South Africa flagship on green mobility: Johannesburg Metrobus, Part I: Greening the future fleet

This research focuses on an emissions control strategy for the Metrobus fleet in Johannesburg, South Africa. While Metrobus has not set any fleetwide emissions reduction targets, both the Johannesburg Integrated Development Plan (IDP) for 2017/2018 and South Africa’s National Green Transport Strategy (GTS) have endorsed deployment of diesel dual-fuel (DDF) engines as a key technology solution for reducing greenhouse gas (GHG) emissions. DDF technology converts a diesel engine into a dual diesel and compressed natural gas engine, and the national GTS is South Africa’s government plan for the sector in support of meeting its nationally determined contribution under the Paris Agreement.

This first of two papers presents an assessment of technology and fuel pathways, emissions modeling, and total cost of ownership analysis. The authors find that although DDF buses provide a minor GHG emissions benefit relative to older diesel buses in the current fleet, the benefit is not enough to offset the increased activity projected for the fleet in the future. The ongoing procurement of DDF buses with no DDF optimization program and no change in the existing fuel mix would increase, not decrease, fleetwide GHG emissions. This would not contribute to achieving South Africa’s climate goals.

Nonetheless, other technology and fuel pathways that are available to Metrobus could meet and even exceed goals. Results show the procurement of dedicated Euro VI gas engines in the near term, accompanied by a transition from fossil gas to biomethane, can deliver a 55% reduction in fleetwide GHG emissions by 2040. Alternatively, the procurement of Euro VI diesel engines in the near term, operated without coal-to-liquids fuel and followed within 10 years by the exclusive procurement of zero-emission engines, would deliver a 73% reduction in fleetwide GHG emissions by 2040. Part II of this work examines the environmental and operational performance of the DDF buses by focusing on fuel consumption and real-world emissions.