Maintenance tasks are not very different from one tunnel to another when there is similar equipment. However, some tunnels have specific features (dense and non-stop traffic, very long diversion route, etc.) that make total or even partial closures of the tunnel very difficult. In this case, the operator may have to maintain a certain operational level, while maintenance interventions are being carried out. This is possible only by deploying special measures that should take into account not only the safety offered to the users but also the safety of the maintenance staff.
Chapter 2 of technical report 2008R15 "Operation of existing urban road tunnels" defines the conditions for carrying out maintenance when the tunnel is in operation.
The same difficulties as those mentioned above are likely to be encountered during a refurbishment of equipment in a tunnel that cannot be closed down easily. With regard to maintenance interventions, this type of works may require several weeks, or even several months to be completed. Consequently, more elaborate (and often costlier) measures have to be planned.
Chapter 6 of technical report 05.13.B "Renovation of tunnels" discusses aspects relating to refurbishment.