Alternative fuels and propulsion systems and the future ofroad tunnel design

Alternative propulsion systems, including battery-electric vehicles, are becoming more prevalent. Whilst such vehicles remain a small overall proportion of the vehicle fleet, the combination of impacts of Government policy and technological advances in alternative fuels is expected to accelerate their increase in numbers on the road and in tunnels in coming years. There may also be particular initiatives in certain geographical areas, such as on airport land for example, where much higher proportions of alternatively fuelled vehicles are seen much sooner than on the open road. As a result, tunnel safety risk (including fire) is expected to change with time. This paper assesses the nature of the most common alternative fuels, their prevalence and the particular vulnerabilities of these types of vehicles to events that may result in fire or toxic release. The paper then assesses the potential consequences of incidents involving these vehicles with particular attention paid to fire characteristics and toxic emissions and their impact on tunnel users and on intervention strategies. The paper draws on the most recent research and testing in this field and provides discussion on impacts on tunnel safety design and operations.