A proposal for evaluation of energy consumption and sustainability of road tunnels: The sustainability vector

https://doi.org/10.1016/j.tust.2017.02.008Get rights and content

Highlights

  • Energy consumption and sustainability of tunnels are critical issues.

  • Energy consumption, landscape integration and construction costs are quantified.

  • This quantification is implemented by three parameters scaled from 0 to 5: e, l and c.

  • A “sustainability vector” to check tunnel sustainability is proposed.

  • A labeling system as tool for Public Administrations is proposed.

Abstract

In the last years, besides traffic safety, two aspects of road tunnels have become really critical: energy consumption of the lighting installations and landscape integration of the portal gate. However, both aspects have been considered from different perspectives, and their development and advances seem to follow separate paths. In this work, energy consumption and landscape integration, together with the cost of portal construction, are proven to be strongly related when considered from the common framework of sustainability and its implications in a necessary global Policy for road tunnels. Departing from the evaluation of real tunnels in a real highway, three quantitative parameters ranged from 0 to 5 (energy consumption parameter, landscape integration parameter and construction cost parameter) are proposed to build a more general tool, the sustainability vector, that gives account of the degree of sustainability and highlights the necessity of corrective actions when necessary. Depending on the values of its module and director angle, a labeling system ranging from A to D, is proposed for the use of Regulatory Bodies and Public Administrations in matter of tunnel classification and sustainability requirements. According to this system, two of the tubes analyzed reach the “A” labeling, whereas two are “B” and six are “D”.

Introduction

One of the most challenging and singular strategies developed by Mankind to get over the natural difficulties and expand its activities has been the construction of tunnels. After several centuries going through mountains or under rivers in quite rudimentary ways, the current degree of development of tunnels exceeds by far the expectations just some decades ago.

However, the design and construction of road tunnels still has serious problems, not only from the constructive and geotechnical perspectives, but also from their performance and maintenance once they are working. Thus, the most prominent problems of road tunnels are traffic safety, energy consumption and landscape integration. This last pretends that tunnels do not appear as artificial discontinuities in Nature, but as part of the landscape itself.

The close relationship between traffic safety and energy consumption has been known and assumed for ages and considered by Regulatory Bodies and Working Groups in their recommendations for tunnel lighting (CIE Publ. 88, 2004). In many aspects, this topic can be considered as an isolated problem, but the relationship between landscape integration and these last is not so well-known nor properly used so far. These problems of road tunnels will be considered in this introduction.

The main problem when drivers go into road tunnels is the visual adaptation from the external luminous conditions to the internal ones. This is due to the slow adaptation of the human visual system, that makes people functionally blind during a too long period when lighting levels are suddenly decreased (CIE Publ. 88, 2004), that is, in the transition from high levels of illuminance (the so called photopic conditions) to lower ones (mesopic conditions), where illuminance is the received luminous flux per unit of surface. It is measured in lux. This eventuality is unacceptable in driving, where one single second of visual impairment when travelling at 100 km/h, means 28 m of uncontrolled driving with the subsequent danger for vehicle's occupants and other users of the road travelling near them. This problem is specially dramatic during daytime and good meteorological conditions, when going into road tunnels means the transition from bright to darker environments.

Thus, the solution to achieve a smooth visual transition when going into these infrastructures is a lighting installation providing very high illuminance levels inside the tunnel, especially in the zone immediately after the portal gate (called threshold zone) and in the zone just before the exit, where glare could impair the visual performance of drivers. A deeper treatment of visual adaptation and other visual aspects of tunnel lighting such as luminance contrast, contrast revealing coefficient (ratio between road luminance and the vertical illuminance on one specific location of the tunnel, qc=L/EV), black hole effect, flicker effect or glare can be found in several standards like CIE 88:2004 (2004) and some of the references cited in this section like Gil-Martín et al. (2011). Given that the target of this research is the provision of new tools to evaluate and improve the sustainability in tunnels, this article will not treat these concepts in depth

The necessary high levels of illuminance, make tunnel lighting extremely expensive in economic terms (the yearly invoice due to lighting in a not extremely long road tunnel can be millionaire), but also in environmental terms (higher CO2 emissions due to energy consumption and manufacture of more luminaries and electrical material), sustainability (higher demand and increase of prices of raw materials for more luminaries, light sources, wiring or ballasts), maintenance (a higher number of luminaries and light sources requests more frequent maintenance operations, that are especially dangerous and expensive in tunnels because they require total or partial traffic interruption) and other concepts.

Hence, the positive impact of high illuminance levels for safety is seriously counteracted by other important effects like energy consumption. This makes almost impossible to split the binomial tunnel safety-tunnel lighting into two separate problems.

In the last years, several lines of active research have been developed to reduce the impact of lighting without impairing traffic safety in tunnels. On one hand, different strategies to decrease the required electric lighting in the threshold zone have been studied: use of road pavements improving the reflective efficiency in order to reflect the same luminous flux with lower illuminance (Salata et al., 2015a); optimization of luminaries distribution (Pachamanov and Pachamanova, 2008), use of intelligent systems to optimize the luminous flux depending on the external conditions of natural light and other eventualities (Leitao et al., 2009, Caicedo et al., 2014, Salata et al., 2016) and forestation of tunnel surroundings with low reflectance plants to decrease the luminance (luminous flux per unit of surface and solid angle in the direction of observation) in the driver eye (López et al., 2014, Peña-García et al., 2015). This last strategy, consisting on the consideration of vegetal species for several purposes has been also frequently considered in other kind of buildings besides tunnels (Salata et al., 2015b; Bernardi, 2016).

In parallel, the use of natural light to complete the required illuminance levels diminishing the electrical light supply, has considered several possibilities like shift of threshold zone out of the tunnel with pergolas (Peña-García and Gil-Martín, 2013, Gil-Martín et al., 2015), translucent tension structures (Gil-Martín et al., 2011, Peña-García et al., 2011, Peña-García et al., 2012), and other kind structures (Abdul Salam and Mezher, 2014, Drakou et al., 2015, Drakou et al., 2016, Wang et al., 2015). Introduction of sunlight into the tunnel without shifting the threshold zone with light-pipes (Gil-Martín et al., 2014, Peña-García et al., 2016) and optical fibers (Qin et al., 2015) is also under consideration with promising results.

One of the strategies above to reduce the consumption of electrical lighting installations, precisely forestation of portal surroundings, is the nexus with another target of this research: landscape integration.

Landscape integration of road tunnels is one aspect included in the broad issue of environmental impact of roads and civil infrastructures. Tunnels are effective solutions to reduce environmental impact of roads hiding them, but their negative effects are concentrated at the portal. According to Peila and Pelizza (2002) “the architectural and landscape aspects related to tunnel portals become very important as the awareness of environment protection by designers gives rise to elevated concerns of integrating an infrastructure with its surroundings”.

Beyond structural and geotechnical difficulties, landscape questions are clearly perceived by drivers and have a deep impact in safety due to visual distractions. Hence, the greening of tunnel entrances is one important challenge (Depei, 2006, Lingli and Dongping, 2008, Fei et al., 2012). As shown in the case of China (Fei et al., 2012), there are several ways to solve the landscape integration of tunnel portals, but they can be summarized in two: promoting its artificial character by structures design and decorations or increasing the environmental integration by mimic them with their environs. At this point it could be considered that a more complete and sustainable landscape integration is linked to an entirely forested portal.

In summary, items 1.1 and 1.2 above show real efforts to solve important problems concerning road tunnels, but they have been considered from separate perspectives in both, technical and regulatory aspects. However, as shown in the following sections, there is a clear link between landscape integration, energy savings and cost of the infrastructure. Hence, a higher and common perspective achieved with an effective Policy in matter of sustainability via an easy labeling system can be a good solution.

This work develops and presents a quantitative parameter and one associated labeling system allowing a quick and unified handling of energy consumption and landscape integration together with construction costs that, up to date, were considered like different problems. Some simple considerations will allow Public Administrations and Regulatory Bodies to evaluate the status of one tunnel and foresee the necessary actions to enhance its sustainability and decrease its energy consumption from a global perspective.

Section snippets

Purpose of the work

Departing from the road tunnels in one given infrastructure, the Trans-European highway A7, the phases of the work have been the following:

  • (1)

    Quantification of the energy consumptions due to the electrical lighting with a scale.

  • (2)

    Quantification of landscape integration of portals in terms of forestation with a scale.

  • (3)

    Quantification of the construction costs of the portal gates with a scaled score.

  • (4)

    Construction of a compact parameter (the sustainability vector) from the defined scales to quantify the

Materials and methods

To carry out the objectives described above, 26 last generation tunnels have been considered. They are placed in one of the most challenging, strategic and modern infrastructures in Europe, the Trans-European highway A7, also called “Mediterranean Highway N-340”, in Spain (Fig. 1).

The choice of this highway arises from its high traffic intensity. It makes its tunnels specially critical in matter of road safety and, hence, their lighting requirements are specially strict.

Table 1 shows the

Results

Once the scales to quantify electrical consumption, landscape integration and construction costs are defined, the tunnels under consideration have been scored. Due to the recent construction of the Trans-European highway A7, the parameters e, l or c cannot be presented in some cases (tunnels still in construction or data not available yet).

Conclusions

The presented proposal provides a labeling Policy filling the current gaps in matter of sustainability of road tunnels from a global perspective integrating energy consumption, landscape integration and constructions costs of the portal gate.

Departing from three parameters e, l and c, scaled from 0 (worst) to 5 (best) to quantify the energy consumption of the lighting installation, the landscape integration of the portal in terms of vegetation and its price of construction, several tunnels in

Funding

This work was supported by the Spanish Ministry of Economy and Competitiveness as part of the Research Project ENE2015-67031-R (MINECO/FEDER).

References (31)

  • U. Bernardi

    The outdoor microclimate benefits and energy saving resulting from green roofs retrofits

    Energy Build.

    (2016)
  • P. Blaser et al.

    Tunnel lighting: method of calculating luminance of access zone L20

    Light. Res. Technol.

    (1993)
  • Caicedo, D., Pandharipande, A., Willems, F.M.J., 2014. Light sensor calibration and dimming sequence design in...
  • Commission Internationale de l’Éclairage, CIE, 2004. Guide for the lighting of road tunnels and underpasses, CIE Publ....
  • Z. Depei

    Greening design of portal part of tunnel and case analysis

    Sci. Soil Water Conserv.

    (2006)
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