Comparative Analysis of Ventilation Codes for Road Tunnels in different regions and Optimization of Calculation Coefficients

• The airflow requirement calculation methods from different regions were compared • Vehicle pollutant emission tests were conducted under various conditions • The annual attenuation coefficient a in the code has been revised • A modified formula for altitude coefficient f h has been obtained The current design codes for highway tunnel ventilation in China, as evidenced by field investigations, significantly overestimate the airflow required to dilute CO and soot, resulting in excessive infrastructure and operational expenses. To optimize China's highway tunnel ventilation design code, the airflow requirement calculation methods from Chinese, EU, and Japanese codes were compared. Vehicle pollutant emission tests were conducted under varying vehicle types, speeds, gradients, and altitudes. The annual attenuation coefficient a and altitude coefficient f h used in airflow requirement calculations were optimized. Results indicate that calculation methodologies across regional codes share fundamental similarities, though they employ differing base emission values and correction coefficients. Measured vehicle CO and soot emissions were substantially lower than values calculated under Chinese codes, reaching a maximum of only 33.9% of calculated values under various operating conditions. The a for base emissions in Chinese codes is low; it is recommended that the range for a be revised to 2.5% ∼ 3%. With increasing altitude, the exhaust flow rate of vehicles under standard conditions decreases linearly. At an altitude increase from 500m to 4140m, the CO concentration in exhaust gases during idling rose from 60ppm to 612ppm, representing a tenfold increase; the light extinction coefficient increased from 0.008 to 0.021, a 2.6-fold rise. Fitting of measured data under various operating conditions yielded a modified formula for f h when calculating the air volume required for dilution of CO and soot. These findings are intended to provide reference for updating Chinese codes and optimizing the design scale of tunnel ventilation.