With the concentration of vehicular exhaust possible from placing vehicular traffic into tunnelways, road tunnel design has evolved with the innovation of ventilation systems to disperse vehicular exhaust. With the concerns regarding the release of such exhaust emissions into the general atmosphere, environmentalist groups overseas, particularly in Australia, have called for highway tunnels to be equipped with ventilation systems that include filtration (rather than simply dilution, as customarily practiced in much of the world, including the United States.
Road tunnels, urban air pollution and filtration - the issues.
Electrostatic precipitation: Valuable for removing particulate matter.
Used in Norway, Japan and Australia
New clean air legislation in Austrialia:
An Act to amend the Roads Act 1993 to require pollution filtration equipment to be installed and maintained that will remove particulate matter from air exiting the M5 East motorway tunnel, the proposed Lane Cove Tunnel and the proposed Cross City Tunnel.
Valuable for removing oxides of nitrogen and sulfate dioxide
Under experiential use in Norway, Austria and Japan is a gas purification system to remove from the air oxides of nitrogen as well as sulfur dioxide. Far from increasing costs, the Norwegian experience suggests that if air-cleaning technologies are included in the design from the beginning the overall expenditure is reduced.
Filtration equipped Tunnels: RX for reduced pollution
Road tunnels equipped with exhaust filtration would tend to reduce exhaust emissions into the general atmosphere by so diverting/accepting traffic, particularly if so providing regionally more direct routes, thereby accommodating greater human activity within a given developed region, and improving the economic competitiveness of older more built up, more pedestrian and transit friendly cities.
The use of filtration in new road tunnels has been advocated by environmentalist activist Bernard Saunders in the New York City Metropolitan region, for a new combined vehicular railway/highway tunnel for relocating the I-287 Cross Westchester Expressway underground
And for CO2: