Road traffic and air pollution. As the 1997 ‘Inquiry into Urban Air Pollution in Australia’ noted, a significant proportion of urban air pollution (40% to 60%) comes from road transport. Diesel trucks are estimated to produce 70 - 80% of fine particulate, recently identified as a major cause of premature death. In a study recently completed across France Austria and Switzerland, the health costs resulting from air pollution were more than the total cost of motor vehicle accidents, including medical costs. Traffic congestion and stop-start driving conditions significantly increase road traffic sourced air pollution on a per trip basis and also have significant cost and greenhouse gas implications, with fuel consumption being increased by up to 50% under congested conditions. 

The place of road tunnels. An efficient network of motorways has the potential to reduce traffic congestion, and consequently fuel consumption and air pollution. However, surface motorway construction in urban areas gives rise to problems including localised air pollution, noise, loss of amenity to local residents, fragmentation of communities and reduction in property values. Road tunnels are being used increasingly to facilitate the development of integrated motorway systems as they overcome many of these disadvantages, with several thousand being built world wide in the last twenty years.

 Problems with tunnels. The drawback of road tunnels is the expense and difficulty of providing efficient ventilation for the safety of the users and the discharging of tunnel exhaust with its concentrated load of vehicle emissions. While vehicle exhausts on surface roads are dispersed along the length of the motorway, in tunnels, ventilation outlets collect this exhaust and release it all in one or two locations, through stacks or portals. Ejection of polluted air horizontally from the tunnel ends is called ‘portal emission’.

People living within 400 to 500 metres of early tunnels using longitudinal ventilation systems and portal emission experienced increased rates of respiratory and cardiac illness. This led to the use of more complex and expensive systems of ventilation and the construction of high vent stacks to disperse the pollutants eg the Sydney Harbour tunnel.

The efficiency of dispersal depends on the height of the stack, the velocity with which the gas is ejected and the nature of the surrounding terrain or buildings. Besides increased construction costs, the cost of running these ventilation systems can be up to twenty times that of a simple longitudinal ventilation system, where the moving traffic provides most of the energy required. The potential for stacks to concentrate pollutants has led to extensive and determined public opposition by the communities likely to be affected in every major Australian road tunnel project.

Overseas development. Environmental and economic factors led, first, the Japanese, and then the Norwegians, to research the use of electrostatic precipitators to remove particulate matter from tunnel air to retain the cost advantages of longitudinal ventilation systems.

The use of electrostatic precipitators within tunnels has led to improvements in external air quality and significant capital and operational cost reductions. Both Japan and Norway have developed different types of installation techniques, with 90 and 95% particulate removal efficiencies achieved. The Norwegian equipment appears to have reached the highest stage of development while the Japanese with their large number of installations and high proportion of diesel vehicles have optimised their installations. Contrary to the claims made by the RTA that electrostatic precipitators are not effective against small particles (ultra fines), an acceptance test in 1999 of a recent Norwegian installation in Korea, removal efficiencies of 94% to 97% were achieved with fine particle efficiencies between 88% and 95% while the tunnel was actually operating. A recent development has boosted these efficiencies to 92% for particles between 0.3µm and 0.5 µm and above 95% for all others. The German developments, which are supported by the government, are limited at the moment to advanced development, with a future installation planned.

Filtered tunnels are about to be constructed in Vietnam, Korea and Germany, with several planned elsewhere in Europe and Asia. 

Treatment of other pollutants. The other major pollutant in tunnel exhaust are the oxides of nitrogen (NOx) which includes nitrogen dioxide (NO₂).The importance of carbon monoxide as a vehicle pollutant has decreased by about 75% since the introduction of catalytic converters as has lead from petrol. Sulphur dioxide will decrease with the introduction of low sulphur fuels, however volatile organic compounds including benzene may show a slight increase but from a low baseline.

Only nitrogen dioxide (NO₂) is immediately dangerous to health but both are components of great concern as general air pollutants. The Norwegians (ABB) have developed an effective means of removing NO₂ (but not the remainder of the NOx.) and have installed it in the recently opened Laerdal tunnel, which is the world’s longest tunnel. The Japanese have done extensive work on this problem but have no installations and the German Clair system also appears very promising in removing both NOx and a range of other pollutants.

 Energy and Greenhouse implications. According to the NSW RTA, the energy cost of the ventilation system for the M5East will be 32 Gigawatt hours per year or about $2.5 million. This is enough energy to run the average country town. The Swiss experts at the June 2000 international tunnel conference, after referring to their government’s insistence on energy efficiency, described a similar tunnel constructed recently with an energy consumption between 1/50 and 1/100 of this. Applied to five or six Australian tunnels, such savings would result in a total reduction in greenhouse gases of between 150,000 and 250,000 tonnes per year. In addition the improved traffic flow promoted by the tunnel will reduce greenhouse gas production by a greater amount.

Why is the use of the technology not more widespread?

Outside of Japan, the technology has only been available for the last 10 years and can only have been regarded as demonstrated for the last 5 years. In Australia some appropriate considerations are:

• Few new tunnels are being built in the US or Western Europe (except in Norway).
• Due to the long development times of tunnels, decisions taken about appropriate ventilation technologies are overtaken by recent technical developments and an increasing understanding of the adverse health impacts of vehicle pollutants especially fine particulate matter. In part these decisions were based on the assumption that the ‘improved’ (EURO) motor vehicle emission standards will quickly bring about a significant reduction in adverse health effects, however this now suggested to be less likely, especially in the case of particulate matter.
• Instrumentalities such as the RTA appear unwilling to promote change because of their inherent conservatism, an understandable unwillingness by senior policy makers to admit that they may have been wrong or even sufficiently forward looking and a fear that a decision to fit such equipment would lead to community demands for ‘retro-fitting’ to other tunnels.
• The NSW and Victorian road authorities seem unwilling to accept the most recent research which indicates that the use of filtration in appropriate ways can decrease the cost of running tunnel ventilation systems and associated energy consumption. They have only been prepared to consider filtration as an ‘add-on’ to something already constructed rather than as an integral part of a rationally designed ventilation system.

These three considerations lead to a classic "Catch 22" situation where desirable and economically efficient developments are prevented from occurring. It is now absolutely clear that the extra $30 million expended on moving the M5 EAST stack could have paid for the filtration of both the M5 East and the Eastern Distributor, both in Sydney.