CHALLENGES

According to the Austrian standard RVS 09.02.41 (“Guidelines and Regulations for Road Construction”), after installing new luminaires or replacing retrofits in road tunnels, it is mandatory to carry out light measurements on the tunnel roadway and walls.

The purpose of the measurements is:

• To confirm that the completed calculations meet the tender criteria:

• • the required overall and longitudinal uniformity
  • the needed levels of illuminance and luminance

• To verify the accuracy of the calculated results
• To confirm that the applied optics are correctly aimed

The measurements are carried out exclusively at night, when the tunnel is dry, to ensure accuracy and eliminate external influences such as daylight or reflections from wet surfaces.

Illuminance is measured in all tunnel zones (entry, transition, interior, and exit) based on tunnel length (short or long) and the number of traffic lanes to obtain comparable, standardised results.

SOLUTIONS

Since the Walchshof Tunnel is a long tunnel without a breakdown bay, according to RVS, we applied a measurement methodology with clearly defined grids of measurement points:

• For tunnels with two lanes, the measurement field consists of seven points along the length and six across the width, yielding a total measurement grid of 7×6 points.
• For the walls, a 4×3 measurement grid was used at heights of 0.20 m, 1 m, and 2 m above the roadway, while along the length, only the odd-numbered points (1, 3, 5, and 7) were measured. Both the right and left walls are measured.

We used a calibrated camera specialised for measuring luminance (cd/m²) and a professional lux meter for precise measurement of illuminance (lx).

Based on the results, overall and longitudinal uniformity were calculated, applying the appropriate maintenance factor.

Table 1 presents an example of the Walchshof Tunnel in the Prague direction, where we compared the required values specified in the tender, those calculated using the software tool, and those measured on-site with specialised equipment.

The results are presented for the entrance (EFB) and interior (ISB) zones on both the roadway and walls (RW – right wall, LW – left wall).

                                                    Table 1: Tunnel Walchshof – Measurement Results

Benefits for the investor

• On-site measurements confirmed the reliability of the tunnel lighting design, calculated and optimised using the software tool.
• All measurement procedures were carried out with calibrated instruments under controlled conditions, ensuring accurate and reliable results that verify the correct aiming of the optics and full compliance with the prescribed criteria.
• It was demonstrated that results can vary significantly in certain cases, highlighting the importance of precise information on the roadway type and the reflection coefficient — parameters that have the greatest influence on photometric values.

• Traffic safety has been ensured by correctly optimized and verified lighting levels within the tunnel.

The risk of additional costs and subsequent corrections has been reduced, as the designed values were confirmed through on-site measurements.

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