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Road Tunnels Manual
Following construction, the unavoidable deterioration of tunnel ventilation equipment reduces the ability of the system to maintain the required safety and performance levels. In addition, new safety measures may be required for technical reasons or because of changes in the tunnel environment.
Appendix A.5 "Ventilation systems" of the PIARC report 2012 R20 "Assessing and improving safety in existing road tunnels" identifies some examples of weak spots for existing tunnels, explaining why it is often necessary to make modifications to the ventilation systems of existing tunnels, including among others the following:
In addition, chapter 6 "Ventilation" of the PIARC report 2016 R19 "Complex Underground Road Networks", explains the reasons that make the refurbishment of the ventilation systems of the complex networks considerably more complicated than in conventional tunnels and section 3.1 "General aspects relevant for design and refurbishment" of the PIARC report 2008 R15 "Urban Road Tunnels: Recommendations to managers and operating bodies for design, management, operation and maintenance" explains some general aspects that also impact the capacity to conduct refurbishment programs for this kind of infrastructure.