Road tunnels: Vehicle Emissions and Air Demand for Ventilation

The design of a road tunnel ventilation system must consider fresh-air demand for maintaining in-tunnel air quality during normal and congested traffic operations and the control of smoke and hot gases in case of fire. The ventilation capacity to manage a fire incident frequently drives the ventilation sizing in highway and non-urban tunnels. Nevertheless, the fresh-air requirement for dilution during normal and congested operation, or special environmental constraints, can be dominant in tunnels with high traffic volumes and frequent congested traffic. This report provides emission rates and an assessment methodology to support the tunnel ventilation system designer in establishing the minimum fresh-air demand for adequate in-tunnel air quality and visibility thresholds.
The emission standards for new vehicles are becoming more stringent and the vehicle fleet is constantly being renewed. Therefore, the data for calculating vehicle emissions and the resulting fresh-air demand requires updating on a regular basis. This report provides the emission rates for exhaust pollutants (CO, NOX and PM), as well as the appropriate factors for non-exhaust particle emissions for passenger cars, light-duty commercial vehicles, and heavy-goods vehicles.
In recent years many international programmes have been undertaken to extend the existing database for emission rates for road vehicles. These programmes have provided updates to data for existing vehicles and have added factors for vehicles in accordance with upcoming emission standards. Factors representing driving situations in road tunnels have now been developed by PIARC for the purposes of this report and a dataset for tunnel ventilation design has been established. This dataset is intended for ventilation design purposes and differs from emission data used for environmental assessments. Specifically, in the derivation of factors relevant to tunnel ventilation system design, a conservative approach is taken where specific factors may lie within a range.
Data collection and methodologies to derive fresh-air volumes are similar to those described in PIARC’s previous reports concerning emission estimations for ventilation design. However, the emission rates found in older reports are outdated. Vehicle legislation has enforced more stringent emission rates since their publication, and vehicle technology has rapidly advanced, resulting in lower emissions.