ANSI C136.27-2021: Tunnel Lighting And Underpass Luminaires

As our road networks become more crowded, the use of tunnels and underpasses is expanding, both to improve traffic flow and to protect local environments from increased traffic exposure. Maintaining adequate, homogenous illumination in the interior of tunnels and underpasses is critical to allowing drivers to quickly adjust to the light within, identify potential obstacles, create maximum visual comfort, and negotiate their passage. ANSI C136.27-2021: Roadway And Area Lighting Equipment – Tunnel Lighting And Underpass Luminaires is used for illuminating roadway tunnels and underpasses.

What Is ANSI C136.27?

ANSI C136.27-2021 covers luminaires used for illuminating roadway tunnels and underpasses. The requirements in this American National Standard are limited to general attributes of tunnel luminaires because of the wide variety of possible designs.

Reliable Roadway Tunnel Lighting

Within tunnels, corrosive atmospheric conditions (due to the relative humidity within the tunnel, the concentration of SO₂ and Cl^– pollution, and particulate pollution such as brake dust) are common and maintenance access can be limited. Consequently, implementing reliable performance of the lighting system is critical, as are certain operational maintenance requirements. The aims of tunnel lighting include:

To allow traffic to enter, pass through, and exit the enclosed section safely
To assist with maintaining the traffic flow
To assure driver safety

What Are the 5 Zones of Tunnel Lighting?

The amount of light required within a tunnel is dependent on the level of light outside and on the point inside the tunnel at which visual adaptation of the user must occur. As such, the requirements for tunnel lighting can vary depending on the specific location within the tunnel, such as the entrance, middle section, or exit. When planning the lighting of a tunnel, there are 5 key areas to consider:

Access Zone (ready to enter):not within the tunnel itself, this is the stretch of road leading to its entrance. From this zone, drivers must be able to see into the tunnel in order to detect possible obstacles and to drive into the tunnel without reducing speed.
Threshold Zone (entrance lighting): the entrance to a tunnel is a particularly important area for lighting because it serves as the transition zone between the outside environment and the tunnel. The lighting in this area should be bright enough to allow drivers to adjust their eyes to the change in lighting conditions without causing glare or discomfort.
Transition Zone (transition area lighting):the area directly after the threshold zone and the luminance should be progressively reduced to allow the human eye to adapt.
Interior Zone (middle section lighting): the middle section of a tunnel is typically the longest and most uniform section, and the lighting requirements for this area can vary depending on the length of the tunnel and the speed of traffic. These luminaires should be designed to provide uniform light distribution throughout the tunnel with minimal light spillage outside the tunnel.
Exit Zone (exit lighting):the transition zone between the tunnel and the outside environment. This zone of the tunnel has increased the luminance level to bright enough to allow drivers to adjust their eyes to the change in lighting conditions without causing glare or discomfort.