In 1990 and 1995, PIARC published the calculation methodology and the emission factors for road tunnel ventilation design. An update of the existing PIARC methodology was necessary, as the emission standards of the vehicles were becoming more stringent and hence the vehicles cleaner. The old version described the emission situation up to the year 1995. This document has been produced by Working Group 2 of the PIARC Technical Committee on Road Tunnel Operations in the framework of its activities btween 2001 and 2003. Due to a steady tightening of emission laws for vehicles and changes in the risk assessment of tunnel fire, some design data may need constant updating. In this publication, new design information and some references are given for sizing longitudinal and transverse ventilation systems.