Objective

To use vehicles, fuel and technology which optimize the balance of efficient operations, output emissions and environmental impact, with regulatory compliance as a minimum standard.

BACKGROUND

Technology

New technology can play a key role in improving environmental performance. However, bus priority on roads and the efficient running of trains can also have a dramatic impact on our emissions performance. In addition, if journey times are reduced more people will use bus and rail services. Reduced running times and increased utilisation are the most effective ways of improving Public Transport’s environmental impact.

Since the early 1990’s, as European exhaust emissions standards for large diesel engined vehicles progressed from Euro 0, through to Euro 5, significant decreases in the following pollutants have been achieved:

• HC Hydrocarbons
• NOx Nitrogen Oxides
• PM10  Particulates
• CO Carbon Monoxide
  
  

These standards as applied to new vehicles achieved significant benefits for the environment including a major contribution to local air quality in towns and cities.

Unfortunately, moving from Euro 0 through to Euro 3 standards had a negative impact on fuel consumption as engines are configured to achieve emission standards. Fuel consumption has also increased on public transport vehicles due to;

• Increases in weight due to
  Improved structural rigidity and crashworthiness
  Additional passenger facilities
• Increased number of double deck vehicles required to meet new school transport policy i.e. elimination of 3 for 2 rule and standing on school services.
   

Euro 4 was introduced during 2007, unlike the previous standards Euro 4 demonstrated an improvement in fuel economy.  This has been further improved with the introduction of Euro 5 in 2009.

Euro 4 & 5 technology

Engine manufacturers have chosen one of 2 different technologies in order to achieve Euro 4 & 5; Selective Catalytic Reduction (SCR) and Exhaust Gas Recirculation (EGR).

SCR uses an additive, Aqueous Urea Solution that is injected into the exhaust gases before they pass through an SCR catalytic converter. In the catalytic converter, the nitrogen oxides are turned into harmless and naturally occurring nitrogen gas and water vapour. With Euro 4, the additive corresponds to about 4% of the amount of fuel, and for Euro 5 about 5%.

The use of SCR technology allows the engine to have improved fuel economy as compared to a similar Euro 3 specification engine.
   
EGR allows Euro 4 & 5 to be achieved without the use of Aqueous Urea Solution. Some of the exhaust gases are cooled and fed back into the engine to achieve a lower combustion temperature, this combined with high injection pressures provide lower levels of NOx and PM10.

THE TRANSLINK APPROACH
 

Technology

Translink is specifying Euro 5 exhaust emissions requirements for all new vehicle deliveries.  With each tender Translink retains an open mind with respect to exhaust emissions technologies. Projected fluid (fuel plus Aqueous Urea Solution) consumption is assessed over the projected life of the vehicle; many other factors are taken into account in selecting the preferred vehicle for a particular application.

Fuel choice – Bio Diesel

Translink uses a 5% bio diesel/95% DERV blend.
An advantage of bio diesel is that it is sourced from grown crops, e.g. rapeseed which is CO2 neutral (apart from the energy to grow, process and distribute), renewable, has no sulphur content and is biodegradable if spilt. There is a small cost advantage but this may be offset by poorer fuel consumption.

Targets

• To achieve an average road fleet age of 8 years and retirement age of 12 years for coaches and 18 years for buses by 2013. This will significantly reduce exhaust emissions in terms of HC, NOx, CO and PM10.
• To optimise fuel efficiency of new road and rail vehicles by selecting appropriate engine ratings, engine technologies, transmissions and final drive ratios.
• To replace passenger trains; older than 20 years with new trains by 2013 creating significant reduction in exhaust emissions and eliminating toilet emissions direct to track.
• Improving public transport fleet generally to assist via modal shift from private car to bus and rail.