|Authors:||Alena Katharina Høye, Tor-Olav Nævestad, Grétar Ævarsson|
|ISBN (digital version):||978-82-480-2245-9|
Full report - in Norwegian only
Negative binomial regression models were developed in order to calculate predicted numbers of vehicle fires, crashes, and breakdowns as a function of traffic volume and several tunnel-related variables, such as vertical grade, speed limit, and twin- vs. single-tube tunnel. The model results indicate that the number of vehicle fires in tunnels increase with increasing vertical grade, especially at grades at or above 7%, and with increasing length of steep grades. The number of vehicle breakdowns is also higher in tunnels with steep grades of 7% or above, than in other tunnels. Other variables than vertical grade (and volume) have little or no effect on the numbers of fires and breakdowns. The number of crashes is not related to vertical grade. It is higher in twin-tube tunnels than in single-tube tunnels, higher at lower speed limits (below 80 km/t), higher in completely straight tunnels than in tunnels with slight curves, and lower in tunnels with a height of at least 4.5 meters than in lower tunnels.