Testing cleaner buses

Basic Information

Mobility solution ID






Trials were carried out in Preston to select the most appropriate clean engine technologies for the city.

Implementing sustainable mobility

In seeking to encourage cleaner and better transport, many CIVITAS cities included the use of clean vehicles and clean fuels in their strategies. As part of the Preston’s efforts towards reducing air pollution and creating a cleaner urban environment, the public transport operator Preston Bus carried out trials of new clean engines that aimed to produce at least a 5 percent saving in emissions and fuel consumption.

Specific objectives were to:

  • test clean engine technologies in the Preston bus fleet to increase engine efficiency, fuel efficiency and reduce environmental impacts, primarily air pollution;
  • use biodiesel to demonstrate its technical feasibility and environmental advantages in city fleets;
  • operate the vehicles on a high-profile route serving the city centre, thereby increasing public awareness of alternatively powered and fuelled vehicles and their advantages; and
  • stimulate the market for alternatively powered and fuelled vehicles in the UK.


The original plan was to assess three hybrid buses, but this proved not to be feasible, as did other alternatives based on refining biodiesel locally. The partners made attempts to purchase suitable hybrid buses but faced a number of barriers: vehicle availability was low, costs were high and government grants were withdrawn on a national basis, significantly undermining the cost to benefit ratio.

As an alternative, trials in both the commercial and school bus fleet operating in Preston were undertaken in partnership with the company Firepower, using their “clean and purge” technology. The objectives for the test group of 10 vehicles were to increase diesel fuel efficiency rates and decrease levels of exhaust emissions to at least the same, if not a greater, extent as was expected by the introduction of hybrid buses.


The disappointing progress of the Firepower trial resulted in only partial evaluation of the measure. Results from the clean and purge engine trials remained inconclusive and the trials were not pursued.

Subsequent trials on three buses with 5 percent biodiesel showed little difference in performance, but it was considered that biodiesel use may have contributed to some sludge build-up. The introduction of biodiesel increased costs for bus operators, who had previously been able to reclaim 80 percent of the duty paid on fuel. Due to difficulties in obtaining a 5 percent blend from recognised suppliers and a competitive price, the local authority began exploring possibilities for local production and supply. National legislation subsequently made a 5 percent blend the UK standard.



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