Tunnel fire safety is a complex problem with no clear solution as yet. Current knowledge of vehicle fire behaviour in tunnels has been established on the basis of a relatively small selection of experimental fire tests, each of which is described. The characteristics of vehicle fires in tunnels are highlighted and issues to be considered when defining ‘design fire for tunnels are discussed. The mechanisms of fire spread in the tunnel environment are presented. The most common fire protection measures used in tunnels are ventilation systems, passive thermal barriers and, increasingly, water spray systems. Each of these three system types are discussed. © Society of Fire Protection Engineers 2016. All rights reserved.