Facilitating and supporting the transition towards more sustainable mobility
Tunnels and underground spaces are key areas for promoting the transition to more environmentally friendly modes of transport. In urban areas, tunnels can be an optimised transport solution, leading to interconnected networks and facilitating the modal shift towards less ‘polluting’ modes (via the creation of underground multimodal hubs). Urban guided transport networks are a good example of this: tens of kilometres of tunnels increase travel efficiency by significantly reducing journey times, thereby helping to promote modal shift (as in the case of the Paris Metro and the future Grand Paris Express). Urban tunnels can contribute both to the decarbonisation of travel and to the transition to more sustainable mobility by promoting active modes (cycling, walking, scooters, etc.) or alternative modes (public transport, carpooling, personal motorised vehicles, etc.).
In rural and particularly mountainous areas, tunnels can reduce the length and gradient of a route, encouraging a shift to rail transport. It is estimated that the new Euralpin Lyon-Turin link and its tunnel will enable 50% of goods transiting through the Alps to be redirected to rail transport, compared with only 10% at present. The reduction in gradients along the route should also lead to energy savings of 40%.
Changes in the vehicle fleet are also part of the transition in mobility, with a growing proportion of vehicles using new propulsion technologies (electricity, gas, hydrogen, etc.). This shift creates new risks in road tunnels that need to be understood and taken into account in terms of operation and safety measures. Thus, when we talk about the transition in mobility, we are talking about both an ecological and an energy transition.
Integrating active mobility modes into existing tunnels
Major cities are currently seeking to reduce road traffic and therefore promote other modes of transport, particularly ‘active’ modes such as walking and cycling.
In addition, the French government has encouraged regions to develop cycle routes and greenways as part of regional cycle route and greenway plans. These are often created on former railway lines that include tunnels.
At the same time, the use of personal mobility devices (PMDs) is growing, albeit not without causing some coexistence issues: scooters, rollerblades and skateboards, which also exist in motorised (electric) versions referred to as EPMDs
A lack of guidance or recommendations
In 2015, French Decree No. 2015-808 of 2 July on the action plan for active mobility and parking aimed to adapt road traffic rules in order to make travel safer and easier for pedestrians and cyclists. However, it made no mention of the issue of tunnels.
In September 2022, the French Prime Minister launched the ‘Cycling and Walking 2023-2027’ plan to redouble efforts and make cycling a permanent part of everyday life for all French citizens. The first interministerial committee meeting on this plan was held on 5 May 2023.
The above context is relatively recent and the vast majority of existing road tunnels were designed to exclude pedestrian and bicycle traffic. To date, there are no guidelines or recommendations on this subject.
Nevertheless, the CETU is regularly questioned on how to design road tunnels with active transport modes in mind. These requests have increased since the pandemic during which numerous cycle lanes were created. The challenge is therefore to support the progression of all active modes of transport by enabling them to pass safely through both urban and interurban road tunnels and on greenways.
CETU research and publications
In the absence of established guidelines for the profession, and in order to help ensure that active modes of transport are properly taken into account in road tunnels, the French-speaking working group of road tunnel operators (GTFE) organized a workshop on this subject in October 2023.
The GTFE proceedings on this topic are available in French here.
In 2024, the CETU launched a specific research programme on the transition to sustainable mobility. The first step will be to take stock of the current situation regarding active transport modes in road tunnels, provide feedback from case studies and identify the difficulties encountered as well as the challenges in terms of regulations and safety. A document, to be published shortly, will present examples of recent bicycle facilities in road tunnels (in urban areas and non-urban areas ).
Technical guidelines will then be developed. They will specify the operation and safety provisions necessary for the integration of active transport modes in existing tunnels, with a focus on aspects such as geometry, signage, lighting and ventilation. Consideration will also be given to the introduction of new active transport measures in intervention and emergency plans. Specific technical guidelines will be developed for tunnels located on greenways.
Identify the risks and challenges associated with new propulsion technologies
New propulsion technologies have been developed to combat global warming and air pollution. Regulatory constraints already apply to public transport operators so that, in the long term, only vehicles running on these new energies will be used. However, specific phenomena linked to these new energies can pose a particular danger in underground environments, both for users and for emergency services. The intervention of the latter can sometimes be made more difficult. All types of underground structures are potentially affected by these phenomena: road and rail tunnels, urban service structures, car parks and other specific structures (waste storage centres, etc.).
There are currently no specific regulations governing the movement of vehicles or trains powered by these new energy sources in underground environments.
CETU research initiatives
In recent years, CETU has conducted several research initiatives to better assess the impact of these new energies on the safety of underground structures. A joint research project with INERIS has led to initial results in terms of analysing and measuring the additional risks associated with these new energies.
At the same time, a French working group called "NERTT " (New Energies and Technological Risks in Tunnels) was set up in 2020. It brings together representatives of the various stakeholders involved in this issue: infrastructure operators, public transport operators and their administrative authorities, and emergency services. This group aims to produce a document setting out the economic, legislative and regulatory framework, as well as the risks and constraints for the various stakeholders.
Despite these studies, questions remain. The CETU’s research work will therefore continue with two objectives:
- consolidate and improve the understanding of technologies (including safety systems), hazardous phenomena and technical mitigation measures external to vehicles;
- advise the tunnel community on how to take these new technologies into account in safety management.
The studies will initially focus on tunnels, both road and rail. Once sufficient knowledge has been established, it will be transposed or adapted to other types of underground environments.
CETU publications
Conference articles
‘Integration of new energy carriers in French specific hazard investigations, overview of principal issues’, C. WILLMANN, P. CHARLES (CETU), Tunnel Safety and Ventilation Conference, Graz, Austria, 2024
‘The use of Natural Gas Vehicles in underground facilities: Application to the Paris-La-Défense underground network’, B. TRUCHOT (INERIS), C. WILLMANN (CETU), P. PERSONNA (Paris La Défense), Tenth International Symposium on Tunnel Safety and Security, Stavanger, Norway, 2023
At the international level, the CETU was also heavily involved in drafting a PIARC technical report on this topic.