Code of practice for the design of road lighting
BS 5489-2:2003 pdf free.Code of practice for the design of road lighting一Part 2: Lighting of tunnels.
NOTE 1 Information on tunnel design, use and operational aspects that affect tunnel design is given in Annex A.
Road and traffic conditions in tunnels can differ considerably from those that prevail on the open road. The design of tunnel lighting installations should take these different conditions into account, particularly with regard to traffic safety.
The object of installing lighting in a road tunnel is to enable traffic to flow through it with the same speed. degree of safety and comfort as on the approach roads.
This aim can be achieved only when road users are sufficiently aware visually of the roadway ahead of them and, in particular, of the presence or absence of other vehicles and possible obstructions.
Driving comfort is an important aspect of the quality of the lighting installations of road traffic tunnels. As a result of feelings of anxiety, drivers are likely to slow down near a tunnel entrance. Sudden drops in speed reduce traffic capacity and might lead to traffic jams and possibly to accidents. A lighting system that helps to overcome any feeling of anxiety can improve traffic safety, increase road capacity and improve driving comfort.
The difficulty of the driving task when approaching and passing through a tunnel is influenced by the
speed, the volume (flow) and the composition of the traffic and by the layout of the road and the tunnel and their immediate surroundings.
The tunnel lighting class and lighting levels are affected by the traffic flow, and the type and mix of traffic, and should be determined in accordance with Clause 5.
NOTE 2 Information on diffornt lighting gvtem i givc.n in Annex B.
4.2 Daytime conditions
The major difference between tunnel lighting and conventional road lighting is in the need for lighting by day. A driver needs to be able to see a certain distance ahead such that if an unexpected hazard appears, the driver can react and stop within that distance. When this distance extends into a tunnel there should be a sufficiently high lighting level inside to maintain visibility. If the lighting level is not high enough, the driver will be unable to see into the tunnel, the so-called “black hole effect”.
During approach and entry to a tunnel, drivers’ eyes become adapted to the darker surroundings. This adaptation is a continuous process with the result that further into the tunnel, providing it is of sufficient length, the lighting level may be steadily reduced until it reaches the constant level in the tunnel interior zone. On emerging from a tunnel into daylight the eye adapts far more quickly to the higher luminance level.
Similarly, rearward visibility should be maintained when leaving a tunnel, to facilitate safe rnanoeuvres within the parting zone.
The lighting of a tunnel should be sufficient to:
— avoid the “black hole effect” when a driver is unable to see into the tunnel:
— reduce the likelihood of a collision with another vehicle (or bicycle or pedestrian):
— enable a driver to react and stop within the stopping distance SD (see 5.1) if an unexpected hazard appears;
— provide visual guidance.
4.3 Night-time conditions
During night-time the “black hole effect” does not exist, as the external luminance values are low. Lower lighting levels are needed in the tunnel than during daytime, with all zones treated in the same manner. (See 5.7.)
4.4 Lighting for different tunnel lengths
Lighting design for long and short tunnels differs according to the degree to which an approaching driver can see through the tunnel to the exit portal from a point at a distance equal to the stopping distance in front of the entrance portal.
The ability of a driver to see through a tunnel depends primarily on the length of the tunnel, although other design parameters also have an effect (width, height, horizontal and/or vertical curvatures, etc.).
The critical factor is whether approaching drivers can see vehicles, other road users or obstacles when their distance from the entrance portal is less than or equal to the stopping distance SD (see 5.1). When the exit portal is a large part of the scene visible through the entrance, other road users and objects can easily be seen silhouetted against the lighter scene behind the exit portal. On the other hand, artificial lighting is needed when the exit portal is in a relatively large dark frame, in which objects can be hidden. This can happen when a tunnel is relatively long in relation to width, or when a tunnel is curved in such a way that only a part of the exit can he seen or the exit cannot be seen at all.
Tunnels shorter than 25 m do not normally need daytime lighting. Tunnels longer than 200 m should always have artificial daytime lighting, to avoid adaptation problems for road users. For tunnels of length between 25 m and 200 m, the method described in Annex C should be used to determine if daytime lighting is needed. If full daytime lighting is needed, it should conform to the recommendations given in Clause 5.
If full daytime lighting is not needed for tunnels of length between 25 m and 200 m, some limited daytime lighting can be provided for tunnels where the traffic flow is classified as“high” (see 5.2), when luminancelevels within the tunnel are low, and during the periods immediately before dusk and after dawn,particularly on overcast days. The decision to provide such limited daytime lighting is a matter for the highway authority.
In order to determine the necessary daytime lighting levels within a tunnel, the access zone luminance should first be determined, in order to determine the threshold zone luminance and the luminance in the other zones.
There are two methods of determining access zone luminance L20. Whenever possible direct measurement at the site should be used, as described in Annex D.
Where direct measurement is not possible, the grid method should be used, as described in Annex E. A method of estimating L2() may be used to provide an interim value for provisional design purposes, but should not be used for the final design.
NOTE 1 The method given in Annex D is preferable, particularly when the orientation of the tunnel is likely to produce different results for each approach.
NOTE 2 A method of estimating L1 is given in Annex F.
5.4 Determination of tunnel zone daytime lighting levels
5.4.1 Threshold zone
The road surface luminance of the threshold zone should be derived from the luminance of the access zone during daytime. The length of the threshold zone is equal to the stopping distance SD.
The threshold zone luminance LLh should be provided during daytime from the beginning of the threshold zone for a length of O.5SD (see Figure 2). The appropriate value of 1? should be selected from Table 3, and the threshold zone luminance Lh should be calculated using equation (4).BS 5489-2 pdf download.Code of practice for the design of road lighting