Comparative Analysis of Diesel-Powered Buses and CNG-Powered Buses in Mass Transit: A Case of Phase 2 of Tanzania’s Bus Rapid Transit

Abstract

Urban transport in Dar es Salaam faces mounting challenges, including congestion, pollution, and rising costs. Diesel buses currently support mass mobility but emit around 548,392.32 kgCO₂e daily, worsening environmental and health risks. With rapid urbanisation, these issues have become more critical. Compressed Natural Gas (CNG) has emerged as a cleaner, more cost-efficient alternative. However, there is still limited empirical evidence on how CNG buses perform within Tanzania’s BRT system. This study aims to compare the performance of the 18-m BRT diesel and CNG buses in Tanzania’s Bus Rapid Transit, especially in phase 2 of BRT. The study compared the energy, economic, and environmental indicators in both buses. The study used a comparative quantitative design to assess diesel and CNG buses. Primary operational data were collected on fuel use, costs, and emissions across multiple indicators (per km, passenger, trip, and day). Secondary data from government reports and literature supported the analysis. Energy was measured in kilowatt-hours, costs in Tanzanian Shillings, and emissions in CO₂-equivalents. It was found that a CNG bus can save energy approximately 67.8% per km, 68.0% per passenger, 68.0% per trip, and 68.0% per day when compared to a diesel bus. On the economic side, the CNG bus consumed around TZS 775 per km, TZS 100.75 per passenger, TZS 15,732.50 per trip, and TZS 235,987.50 per day. This gives an equivalent saving of around TZS 4,495.4 for every kilometre it travels, TZS 588.25 for each passenger it carries, TZS 91,267.60 per trip, and up to TZS 1,368,849.30 in a single day of operation. Overall, the CNG bus showed a significant reduction in energy cost, averaging 85% in all economic indicators.  In emission savings, the CNG bus could reduce about 75.10% in emissions per km, 75.23% in emissions per passenger, 75.10% in emissions per trip, and 75.10% in emissions per day, representing a reduction of nearly 75% across all emission indicators. These findings demonstrate that CNG-powered buses offer a highly sustainable alternative to diesel buses for urban mass transit, particularly in terms of reduced fuel consumption, lower operational costs, and significantly decreased carbon emissions. Transitioning to CNG technology can enhance energy efficiency, promote environmental sustainability, and reduce the financial burden on public transport systems in developing cities like Dar es Salaam.