Use environmentally friendly (low pollution, low noise) vehicles.
Spurred on by the evolution of regulations supporting clean air, the number of choices in vehicle propulsion system is increasing. Technology is evolving to provide new propulsion systems that use clean, alternative fuels and new controls on emissions, resulting in reduced pollution and lower noise levels. At the present time many new technologies are being introduced and market conditions, such as demand and cost of production, are developing alongside. For further information see ► Background information on Common propulsion systems and European emission standards (EURO 1 to EURO 5 and EEV).
Today, bus technology developers are seeking to provide cleaner bus options. Propulsion systems and alternative fuels options now include: clean diesel, mix of bio-diesel and fossil diesel, methane in the form of compressed natural gas (CNG) or biogas, liquid petroleum gas (LPG), hybrid-electric, ethanol, electric and fuel cell.
Because of the range of various fuels and propulsion systems, it is preferable for tendering bodies (e.g. public transport authorities) to only specify particular qualities, such as emission standards, rather than force a specific technology upon an operator. The operator will need to consider a range of factors such as fuel costs, fuel availability, maintenance, reliability, refuelling times, and performance. Likewise, each operator should be able to choose manufacturers based upon their own circumstances.
Note that moving existing vehicle fleets to alternative fuels, where this is possible, may necessitate some engine modification. Importantly, introduction of vehicles with alternative fuels may require depot modifications and the installation of new equipment and facilities.
Energy efficiency of the fleetshould be checked if older buses are in use; in particular if a purchase of second-hand buses is envisaged. Considerably better efficiency can be a positive reason for buying new vehicles.
Higher costs of alternative traction concepts can still be regarded as a problem in many European countries.
Brighton & Hove (UK): The entire bus fleet runs on bio-diesel. The company was one of the first in the industry to use low sulphur fuel as soon as it became available and is also a market leader in the fitment of specialist equipment to reduce pollution of exhaust gases from bus engines. All the operator's modern vehicles have particulate traps fitted on their exhausts.
Graz (Austria): The bus-fleet in Graz runs with a high share of bio-diesel mixed with fossil diesel. Waste oil from food processing (a local recycling project using oil from restaurants and food production industry) is also used for some vehicles.
Reading (UK): Since May 2008 Reading Buses has had 14 bio-ethanol double deck buses on its Premier Route 17, operating around the clock, seven days a week. Using E95 ethanol, these buses are some of the cleanest there are. Unlike E85 ethanol, which includes a 15% petrol mix, E95 ethanol comprises 95% ethanol and 5% additive to improve ignition. Particulate emissions from these ethanol buses are ten times lower than for the least polluting (Euro V) diesel bus. The bio-ethanol fuel also dramatically reduces the emissions of the global greenhouse gas CO2 by more than 95%, earning these ethanol buses the EEV – ‘Environmentally Enhanced Vehicle’ – classification under European emissions regulations.
Background information: European emission standards (EURO 1 to EURO 5 and EEV)
The European emission standard defines the limit for emissions of new vehicles in the EU. In order to give an indication, the respective limits and the respective commencement date for buses are given below (Table 2‑2). In contrast to cars (g/km), emissions of buses and lorries are indicated in g/kWh. Currently, emissions of carbon monoxide (CO), hydrocarbons (HC), nitrogen oxide (NOx), particulate matter (PM) and smoke are part of this standard.
Background information: Common propulsion systems
Internal Combustion Engines: The internal combustion engine fuelled by ultra low-sulphur diesel (ULSD) or compressed natural gas (CNG), biogas with spark-ignition, or ethanol coupled with an automatic transmission, is the most common propulsion system today. Some public transport authorities are testing other fuels such as bio-diesel, diesel emulsion blends and even LNG but these are a small fraction of public transport applications. The impending EPA requirements on emissions in 2007 and 2010 for NOx and PM will require engines with Exhaust Gas Re-circulation (EGR) plus exhaust after-treatment technology.
Trolley, Dual Mode and Thermal-Electric Drives: Electric trolleybus drives powered by overhead catenary-delivered power are still produced today and are planned in limited quantities for operation in tunnel applications. Dual mode systems with an on-board thermal engine (usually diesel) can provide a capability to operate as a trolleybus and as an ICE (Internal Combustion Engine) vehicle off the catenary for specialised operations. Also, a thermal-electric drive, which couples an ICE to a generator, is used as a drive system in vehicles.
Hybrid-Electric Drives: Hybrid-electric drive systems offer improved performance and fuel economy with reduced emissions (e.g. of nitrogen oxides (NOx) and particulates (PM)). They differ from dual-mode systems in that they incorporate some type of on-board energy storage device (e.g., batteries or ultra capacitors). Though the thermal or internal combustion engines used for hybrid drives are diesel in most public transport applications, in a number of cases CNG or petrol-fuelled engines have been used. Fuel economy gains of up to 60% are being claimed in urban service. Operational tests show improved range and reliability over ICE buses. Hybrid buses have entered operation in places such as New York and Seattle. Hybrid drive buses offers numerous operational advantages over conventional diesel buses, such as smoother and quicker acceleration, more efficient braking, improved fuel economy and reduced emissions.
Fuel Cells: A number of operational tests of fuel cell buses are underway this year and next in Europe and the US. Although the price is prohibitive currently, there is great interest in future development to provide zero emissions using domestically produced hydrogen. As far as we are aware, there are no plans as yet for large-scale introduction of fuel cell buses in public transport system applications in the United States or Europe.