Civil Engineering Reference
In-Depth Information
the electric lighting. If the installation is switched in a stepwise manner, the reduction
to lower levels and the increase to higher levels is made in steps of no greater than
3:1 and 1:3 respectively. This is in order to avoid too large and too sudden changes
in the lighting, which could startle drivers at the moment of switching. Some five to
six such switching steps are required to go from the highest level to the night-time
level.
The requirements for uniformity, glare and flicker restriction, as given in previous
sections, should be met for all switching steps.
22.5.4
Maintenance
A great deal of dust and grime, including leaking fuel and oil, is brought into a tunnel
by the traffic passing through it. And there is no rain to help wash away all this dirt.
In addition, the exhaust fumes of the vehicles contain quantities of unburnt carbon
particles. All this may reduce visibility in the tunnel and will certainly produce soiling
of the luminaires, daylight screens and light-reflecting surfaces (e.g. road surface and
walls). This can bring about a rapid deterioration in the various luminances and so
add further to the worsening of the visibility.
All the maintenance aspects for outdoor lighting that have been dealt with in
Sect. 13.5 of Part 1, are also very relevant for tunnel lighting. But cleaning has
to be more frequent for tunnel lighting than for normal, open-road lighting. As to
the method of cleaning the luminaires, washing them with a mechanical scrubber
yields better results than does water-jet cleaning alone. Quite a number of tunnels
are cleaned by special vehicles designed solely for this purpose. It need hardly be
added, that the luminaires should be easy to clean, robust (mechanical scrubbers
can be vigorous in operation), and proof against corrosion from soiling. Their water
resistance should at least be as specified by the classification “jet proof” i.e. IP65.
The tunnel walls should have a surface finish that facilitates cleaning.
The photometers mounted in the access zone, and sometimes also in other tunnel
zones that control the lighting, have to be checked and cleaned as well.
References
AdrianW (1987) Adaptation luminance when approaching a tunnel in daytime. Light Res Technol
19(3):73-79
CIE (2004) Publication 88:2004, Guide for the lighting of road tunnels and underpasses