Managed by Istanbul Metropolitan Municipality, the Ayazağa and Beylerbeyi tunnels are two of the main arteial routes of the European, and the Asian sides of the city, and some of the busiest roadways in the region. With responsibility for maintaining public infrastructure in a safe and efficient manner, the municipality was keen to reduce energy costs, while simultaneously improving the overall illumination within the tunnels.
The original illumination within the tunnels was provided by 400W HPS luminaires but over time these lamps started to fail, resulting in a very dark driving environment and a marked increase in road traffic collisions. The contrast between the dark tunnel and the bright daylight externally also caused problems, as drivers' eyes were often unable to adapt quickly enough to the changing road conditions.
In the Ayazağa tunnel in particular, road safety was a major concern. The tunnel connects two major highways via sharply curving passages, which presents a challenge for driver safety. Despite a speed limit of 80km, vehicles typically enter at high speeds, meaning they must brake abruptly on the approach to the bend. Clear lighting is therefore a crucial aspect of the tunnel's structure, so that drivers are able to recognise the hazard in good time and react accordingly.
The municipality therefore was looking for a solution that would improve the overall illumination in both tunnels, while also driving down the energy consumption and maintenance costs.
With a strong focus on reducing the contrast between the external and internal environment, Current, powered by GE put together an optimized lighting design that minimizes the adaptation drivers' eyes need to make as they enter the tunnels. This design can be controlled to match the lighting levels outside, so the illumination within the tunnel can be raised or lowered according to the time of day.
The design encompasses TLBt and TMBt single and double module tunnel lighting fixtures, which have been specifically designed for use in a wide range of low and high speed tunnels, underpasses and industrial areas. Developed to offer a highly durable and reliable product with a long lifespan of around 60,000 hours, the modules are designed for quick and tool-less maintenance in order to keep operational disruption to a minimum – which is good news for engineers and tunnel users alike.
The new lighting design has delivered a much better level of illumination, which has greatly improved road safety. The LEDs provide a clearer quality of white light than traditional lighting sources – it's been shown that drivers' reaction time (known as mescopic vision) is up to six times faster in white light, while the higher colour rendering also improves obstacle recognition. Similarly, the angle of the LEDs can be more closely controlled than traditional light sources, allowing precision illumination of the carriageway, while minimising glare
What's more, as LED lighting solutions consume far less energy than traditional lamps, the new installation has slashed the energy requirement within the tunnel from 130kW/h to 70kW/h – which will result in a 46 per cent annual energy saving for the municipality. With this saving taken into account, the project will achieve an impressive 3.5 year payback period as well as an annual reduction in CO2 emissions of 100 tonnes.
Yusuf Boyraz, Electrical Engineer at Istanbul Metropolitan Municipality commented: “As two of the busiest roadways in the city, safety was our biggest consideration. Choosing an LED solution has meant that we are able to control the illumination levels much more easily, which in turn has greatly improved visibility and driver reaction times. The number of collisions has significantly decreased since we installed the LED solution, which is a major indicator of success for us.”
