Abstract The strengthening of vehicle emission standards in the Federal Republic of Germany has also served to reduce exhaust emissions in road tunnels. The effect of the stricter standards was investigated by STUVA [Research Association for Underground Transportation Facilities] (Cologne, Germany) and Schindler Haerter AG (Zurich, Switzerland) with regard to the influence of exhaust emissions on construction costs and the costs of operating ventilation systems. The study covered topics such as ventilation systems, vehicle exhaust emissions, fresh air requirements, dispersion of pollutants outside the tunnel, and fire safety standards. The research was sponsored by the Federal Ministry of Transport, Bonn, Germany. In the future, the fresh air requirement will be governed by the traffic states “congestion” and “at a standstill”, in addition to the exhaust components smoke and carbon monoxide. It is essential to introduce particle filters for diesel-engine, heavy-duty vehicles in order to reduce demands on the ventilation systems of tunnels (e.g., for number of fans and space for air ducts) at the planning stage, as well as to reduce power consumption and/or running times of existing ventilation systems. If particle filters are made obligatory by 1995, the fresh air requirement will decrease by about 30% to 45% by the year 2000. Vehicle emission factors are calculated for vehicle speeds of up to 100 km/h for the future design of ventilation systems, up to the year 2000. In the event of fire in tunnels lacking rescue/ escape facilities, the ventilation system must be capable of delivering 80 m 3 (s·km) to 200 m 3/(s·km) of fresh air, depending on the ventilation system. In such cases, recirculation of air must be strictly avoided.