FIRE SAFETY | ROAD TUNNEL RESEARCH


frequency event tree is the initial fire frequency in UK


road tunnels, which was not available when we started developing this event tree, and was the first challenge. Incident rates vary between tunnels depending on factors such as country, location, geometry, etc. In most cases, it is challenging to use global data, which is why corrections and local rates, if possible, ought to be performed. To derive this rate, we collected the historical statics


of fire incidents in UK road tunnels from National Highways, Transport for London (TfL), and Fire & Rescue Service for the year 2021 and earlier. The period considered for analysis for each tunnel depended on the available data and the number of years that the tunnel had been in operation. The average period was 10 years. Eventually, fire incident records of 38 road tunnels on rural and urban roads were collected, which covers 83% of all England road tunnels. The tunnels have a


length of between 156m and 3260m and a total of 1,710,793 veh/km traffic density, which shows that this database is strong enough. These were all the available fire incident data for road tunnels in England


at the time of writing this article. Then this initial fire rate is updated by considering


the length, traffic volume, and gradient of tunnel under study. It is reported that short tunnels exhibit higher crash


rates, and the accident rate decreases as the tunnel lengthens. Amundsen and Ranes6


showed that the


accident rates decrease as the AADT (annual average daily traffic) is greater. DARTS7


Top, figure 2: LBAQRA Quantitative frequency analysis process Above, figure 3: LBAQRA quantitative consequences analysis sub-models


42 | Summer 2025 established an estimation


model for fire rates dependent on tunnel length and traffic density, which are used in the LBAQRA frequency event tree to update the initial fire rate for a specific


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