This report provides guidelines for a step-by-step process for the development of a safety upgrade programme for existing road tunnels, ensuring that the required safety levels are achieved. The report represents the work of PIARC Technical Committee C.4, Working group 2.

A five step methodology is proposed for the development of safety upgrade works:

• Step 1: "establish a safety framework" to confirm or to prescribe the regulatory framework applicable to the existing tunnel in terms of safety. Safety objectives are defined at this stage.
• Step 2: "investigate current condition" to obtain a clear view of the current situation.
• Step 3: "evaluate current tunnel safety level" in order to determine the existing level of tunnel safety.
• Step 4: "define a safety improvement programme" specific to the existing tunnel and focussed on the deficiencies identified in previous steps.
• Step 5: "evaluate future tunnel safety level" after the works; to demonstrate the safety benefits obtained through refurbishment works.

The presentation of this structured methodology is complemented in appendices with examples of the identification of weak spots for existing tunnels and of case studies of tunnel safety improvement programmes.