The ‘’sustainable development’’ concept may have a slightly different meaning from one country to another and its scope may vary. However the most widely accepted concept is based on three main pillars: economic, environmental and societal.
The concept of sustainable development may be applied to different fields or sectors, including road tunnels, in particular for the operation of this type of infrastructure.
As we know, the operation of a road tunnel is highly dependent on the design and construction phases which precede its commissioning. More precisely it is necessary to take account of the effect of solutions opted for during a project’s design phase on subsequent operating conditions. In other words, this means that, if the chosen solution is not ideal, it will be very difficult to optimize it throughout the tunnel’ life cycle. The technical Report 2017R02EN "Road Tunnel operations: First steps towards a sustainable approach’’ is entirely devoted to sustainability issues and in particular, to optimizing the three pillars.
This chapter gives information about the three main pillars of the sustainable development concept. The balance between these pillars should be estimated accurately for each project design. Nevertheless we should have in mind that sustainable development represents a holistic approach of all involved sectors and parameters, as well as an acceptable and balanced weighting of economic, environmental and societal objectives.
The chapter is broken down into four pages:
A tunnel creates wealth. On a national level, the main part of this wealth creation is due to reduced travelling time, notably for goods transport. It should be noted that the economic benefits of investment in road tunnels are a very complex matter and mostly related to subjective evaluation by decision makers. However, the economic arguments behind the decision to build a tunnel will largely consider the benefits of doing so against the costs.
The potential benefits from constructing a tunnel may consider the following range of issues:
The decision-making evaluation behind the costs for installing a new tunnel will need to consider three main elements: investment, operating and maintenance costs. Construction and maintenance costs will need to consider the impacts on road user travel time and vehicle operating costs during scheme construction and for maintenance.
During the construction phase, it is necessary to ensure that all the planned technical specifications are implemented and that the identified objectives are attained. Finally, it is important to be particularly vigilant with regards to financial aspects, so as to ensure that the cost of works remains within the overall allocated budget.
The primary aim of environmental protection is to reduce the impact on air, water and ground to a long-term acceptable level.
The benefits of the construction of a tunnel should consider the greenhouse gas benefits arising from reduction in travel time and vehicle operating costs.
The preservation of the species living around the tunnel may require the set-up of special measures. These measures may be aimed at restoring passageways for certain species or preserving reproduction areas. In some cases, the position of certain technical facilities may be modified (ventilation units, extraction shafts, etc.).
In order to avoid the exceptional presence of these species on the roadway or in the tunnel (which can present significant risks for drivers and for the species in question) specific measures like fencing or enclosures may be necessary.
The use of natural resources should be carefully examined in the design phase, if possible by favouring materials which have the lowest carbon footprint, or by recycling materials already used elsewhere. Also, to minimize the use of energy resources, the design should take into account the energy consumption during both the construction phase (adapt the design to less energy-intensive construction methods) and the operational phase of the tunnel.
With regard to the three components of the environmental pillar (conservation of species, resources and energy), the construction phase has considerable impacts. A tunnel should be built in such a way that the impact on the environment is as low as reasonably practicable. Selected suppliers must:
All the actions planned for the conservation of animal species present in the vicinity of the works or in the vicinity of the finished tunnel must be undertaken in strict compliance with the environmental specifications outlined during the study phase.
The impact of a tunnel on housing conditions and health may be positive for the residents who will no longer suffer from sound nuisances as they will disappear with the construction of the tunnel. It may sometimes be negative for people living near the portals of the tunnel (if the tunnel was badly designed) who will be subjected to increased sound nuisances or higher pollution levels. The installation of noise barriers could therefore be considered a measure for sustainable road tunnel operations.
In addition, we need to examine the impact that the road tunnel may have on the economic attractiveness of areas which previously had poor access conditions.
The points mentioned above on economic appraisal should also be viewed through the lens of social benefits or costs. For instance, by creating new links with a tunnel the journey time for someone commuting to work could be greatly improved and this would yield not just economic but social benefits – for instance with greater time with family and friends through a reduced commute time.
Other aspects for consideration for sustainable options could be feasibility for walking and cycle ways with measures such as dedicated cycle ways that could be used by pedestrians also being built into the design at the outset.
From a social point of view, the construction phase can have quite different effects: either positive or negative.
For inhabitants in the vicinity of the works site, it is clear that the works can pose a nuisance (traffic disruptions, noise, dust, etc.). Suitable measures must therefore be taken to reduce such forms of nuisance, so that residents are disrupted as little as possible.
On the positive side, it is during the construction phase that the impact on employment is the greatest. Tunnel construction requires considerable manpower over a long duration, especially if the size of the tunnel is substantial. This manpower is not necessarily local, but more often than not a considerable part of this manpower is hired near to the works site. Moreover, non-local manpower has an indirect impact on the local economy (hotels, restaurants, etc.).
The main energy-consuming devices in a tunnel during normal operation are:
The respective share of each of these energy-consuming systems varies greatly, depending on the specific characteristics of the tunnel: length, gradient, water ingress, etc. Let us consider, for example, the case of a short tunnel: it will not be ventilated (therefore the ventilation element is removed), but it will be lit with entrance zones covering almost its entire length and, due to its shortness; lighting will be a major energy-consumption factor. In contrast, for very long tunnels, the energy-consumption of lighting will be low compared with the energy-consumption of the ventilation system.
In relation to energy expenditure, the first thing that an operator can do, for any given energy requirement is to play competitors off against each other by consulting several suppliers that provide the kind of electricity to be used (renewable energy). This approach assumes that the installation is optimized in terms of the power installed and the operating times of the various pieces of equipment.
In effect, we have seen that energy expenditure is closely linked to two factors: the power installed per family of equipment and each family of equipment’s operating time.
For each family of equipment, the installed power is assessed during the study phase and is fixed during the implementation phase. Once the structure is operational, the power can mainly be changed during renovation. At this time, it may be decreased if the regulations haven’t changed and if the energy performance of the replacement equipment has improved. It may be increased if regulations have become stricter (for example: greater smoke extraction capacities).
Basically, outside of renovations, if an operator wants to reduce its expenditure on electricity, it can only do so by optimizing the operating times of the installed equipment and by monitoring peak hours.