**4. Results**

Having referenced the current energy consumption to light the tunnels involved in the first phase of Greenlight, Table 3 summarizes the calculated yearly energy savings for each lot and its overall value. The listed values take into account the switching control and the variable absorbed power during the day (day and night hours) and during the year (sunny, cloudy, or rainy days).


**Table 3.** Yearly energy savings—first phase.

For each tunnel, the yearly energy saving represents up to 65% of the current yearly energy consumption related to lighting; the value depends on geographical, tra ffic, and meteorological conditions. At present, the yearly overall consumption for lighting all tunnels managed by ANAS is

about 220 GWh, of which 51 GWh is used for the tunnels involved in phase 1 of Greenlight. Therefore, the average energy saving is 55%: this result has both economic and environmental consequences.

Given the average Italian electricity price is 0.16 €/kWh, the economic results and savings obtained in the first phase of Greenlight are listed in Table 4. Moreover, these savings have environmental implications: the saved tons of oil equivalent (TOE) were calculated. According to the Italian Authority for Energy and Gas, the conversion factor of electric energy into primary energy is 0.187 TEP/MWh, and this is the reference value that was adopted to evaluate the e ffectiveness of the energy e fficiency measures.


**Table 4.** Economic and environmental results—first phase.

Taking into account the expected rebates in the tender phases, ANAS estimated that the actual investment is 30 million euro. Therefore, the economic gains from saving electricity consumption ensure a breakeven point at 7 years after the rehabilitation works, when the project will return its initial investment.

In regard to the environmental issue, the saved impacts from energy non-consumption were calculated using the software package SimaPro 8.0.5.13 [46]. A Life Cycle Impact Assessment was implemented to evaluate the saved environmental impacts in relation to the electricity savings listed in Table 3. The database Ecoinvent 3 was used to assess the parameters describing environmental impacts according to the characterization factors listed in EN 15804:2012+A1:2013 [47]. The examined environmental impact categories (ICs) were: Global Warming Potential (GWP), Ozone layer Depletion Potential (ODP), Acidification Potential (AP), Eutrophication Potential (EP), Photochemical oxidation Potential (POCP), Abiotic depletion-elements (ADP-e), and Abiotic depletion-fossil fuels (ADP-f).

The processes included in the environmental analysis of the transmission of high voltage electricity were electricity production in Italy and from imports, the transmission network and the electricity losses. In order to obtain reliable results consistent with the Italian energy market, the production mix was composed of 36.6% of renewable primary energy and 63.4% of non-renewable primary energy (Table 5).



Table 6 lists the impact categories that were avoided annually due to the total yearly energy saving listed in Table 3.


**Table 6.** Avoided impact categories—first phase.

The Greenlight project represents a big effort on the part of ANAS, the Italian government-owned road company to rehabilitate and improve the lighting systems in its tunnels. The investments are significant, for example, for the rehabilitation works completed in 2018, the total cost was 6 million euros (Figure 2), and in 2019, works worth 13.5 million euros are in progress or planned (Table 7).



Data in Table 7 were also analyzed in order to correlate the required investment to the tunnel length (L): Figure 3 shows the results obtained for 32 tunnels (their overall length is 39,663 m) of phase 1.

**Figure 3.** Tunnel length vs. rehabilitation lighting costs per unit length.

As shown in Figure 3, a correlation curve between *L* and the lighting rehabilitation cost per unit length (*cl*) was identified (Equation (4)):

$$c\_l = 182339 \text{ L}^{-0.901} \tag{4}$$

where *L* is expressed in m and *cl* is in €/m.

The coefficient of determination R<sup>2</sup> of the dashed trend line is 0.87. The obtained curve is valid under two important hypotheses about the cost of luminaries and the layout of the lighting systems.

With regard to the cost, the unit prices comply with those currently valid in Italy [49]; the price of each luminaire ranges between € 395 for elements with less than 3000 lm luminous flux and € 1798 for elements with more than 41,500 lm luminous flux. Regarding the layout of the lighting systems, the number and the position of LED luminaries coincide with those of existing HPS luminaries. Thus, the distance between LEDs could be less without the restriction of having to replace the HPS at the same distance, and the total initial cost of the luminaires in the interior zones could be higher.
