CR 14380:2003

Lighting applications - Tunnel lighting

This standard is valid for all road tunnels and underpasses which are used by the motorised traffic, and which are decided to be lighted.

Eclairagisme - Eclairage des tunnels

Uporaba razsvetljave – Razsvetljava v predorih

General Information

• Status: Withdrawn
• Publication Date: 08-Apr-2003
• Withdrawal Date: 13-Apr-2025
• ICS: 93.080.40 - Street lighting and related equipment
• Technical Committee: CEN/TC 169 - Lighting applications
• Drafting Committee: CEN/TC 169/WG 6 - Tunnel lighting
• Current Stage: 9960 - Withdrawal effective - Withdrawal
• Start Date: 16-Oct-2024
• Completion Date: 14-Apr-2025
• Ref Project: SIST-TP CR 14380:2004 - Lighting applications - Tunnel lighting

Relations

• Replaced By: CEN/TR 14380:2024 - Lighting applications - Tunnel lighting
• Effective Date: 18-Jan-2023

Standards Content (Sample)

SLOVENSKI STANDARD
01-september-2004
Uporaba razsvetljave – Razsvetljava v predorih
Lighting applications - Tunnel lighting
Eclairagisme - Eclairage des tunnels
Ta slovenski standard je istoveten z: CR 14380:2003
ICS:
93.060 Gradnja predorov Tunnel construction
93.080.40 &HVWQDUD]VYHWOMDYDLQ Street lighting and related
SULSDGDMRþDRSUHPD equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

CEN REPORT
CR 14380
RAPPORT CEN
CEN BERICHT
April 2003
ICS
English version
Lighting applications - Tunnel lighting
This CEN Report was approved by CEN on 10 November 2001. It has been drawn up by the Technical Committee CEN/TC 169.
CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,
Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and United
Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2003 CEN All rights of exploitation in any form and by any means reserved Ref. No. CR 14380:2003 E
worldwide for CEN national Members.

CONTENTS
0 Introduction . 6
1 Scope . 6
2 References. 6
3 Definitions. 6
3.1 Tunnel related zones
3.2 Lighting
3.3 Luminances, illuminances
3.4 Traffic related concepts
4 General aspects of tunnel lighting. 10
4.1 Tunnel conditions
4.1.1 Stopping Distance
4.1.2 Tunnel Lighting Requirements
4.1.3 Traffic composition
4.1.4 Road and Tunnel conditions
4.2 Distinction between long and short tunnels
4.3 Lighting systems and contrast rendition methods
4.3.1 Artificial lighting systems
4.3.2 Screened daylight systems
4.4 Aspects common to the various design methods
4.4.1 Flicker
4.4.2 Glare restriction
4.4.3 Lighting control
4.4.4 Maintenance
5 Lighting of long tunnels. 18
6 Artificial lighting of short tunnels and underpasses . 18
7 Emergency lighting. 19
8 Traffic signals. 19
9 Measurement of tunnel lighting installations . 19
9.1 Quality numbers for tunnel lighting installations
9.2 Measuring fields
9.3 Instruments and methods
9.3.1 General
9.3.2 Illumination measurements
9.3.3 Luminance measurements with spot-luminancemeter
9.3.4 Reflection measurements
ANNEXE A1 – L20 METHODOLOGY. 22
A.1.1 Luminance level in the threshold zone
A.1.2 Length of the threshold zone
A.1.3 Lighting requirements for the transition zone
A.1.4 Lighting of the interior zone
A.1.5 Lighting of the walls
A.1.6 Uniformity of the road surface luminance
A.1.7 Lighting of the exit zone
A.1.8 Night time lighting
A.1.9 Glare and flicker
A.1.10 Determination of the luminance in the access zone
A.1.10.1 Approximation of L20
A.1.10.2 Determination of L20
ANNEXE A2 – TRAFFIC WEIGHTED L20 METHOD. 30
A.2.1 The determination of the tunnel class
A.2.2 The lighting of the threshold zone of long tunnels
A.2.3 The length of the threshold and transition zone
A.2.4 The road surface luminance of the interior zone
A.2.5 The exit zone
A.2.6 Non-uniformity of the luminance
A.2.7 The lighting of the tunnel walls
A.2.8 Glare restriction
A.2.9 Restriction of the flicker
A.2.10 Night-time lighting
ANNEXE A3 – VEILING LUMINANCE METHOD AS USED IN THE NETHERLANDS. 34
A.3.1 Introduction
A.3.2 The determination of the required contrast in the threshold zone of a long tunnel
A.3.3 The veiling luminance Lv
A.3.3.1 The determination of the veiling luminance Lv
A.3.3.2 The determination of Lseq
A.3.3.3 The determination of Latm
A.3.3.4 The determination of Lwinds
A.3.4 The determination of the threshold zone luminance
A.3.5 Object and road luminance
A.3.5.1 No daylight influence
A.3.5.2 The influence of daylight falling into the tunnel at the tunnel entrance
A.3.6 Further tunnel lighting design aspects
A.3.6.1 The threshold zone
A.3.6.2 The lighting of the transition zone
A.3.6.3 The lighting of the interior zone and the exit zone of long tunnels
A.3.6.4 Glare restriction
A.3.6.5 Restriction of the flicker
ANNEXE A4 – THE SPACE AND ADAPTATION METHOD AS USED IN France . 40
A.4.1 The principle of the method
A.4.2 The luminaire adaptation
A.4.3 The space adaptation
A.4.4 The time adaptation
A.4.5 Characterising the lighting installation
A.4.6 Calculating road luminance
A.4.7 Algorithm of LCR calculations
A.4.8 Calculation details for one 10 meters step for a rather simple case
A.4.9 Calculating illuminance levels
A.4.10 The results
A.4.11 Road surface luminance of the interior zone at day-time
A.4.12 Night-time lighting
A.4.13 Lighting of the walls of the interior zone
A.4.14 Emergency guidance lighting
A.4.15 Fire emergency guidance lighting
A.4.16 Uniformity of the road surface luminance
ANNEXE A5 – DETERMINATION OF THE NEED FOR DAYTIME LIGHTING OF SHORT TUNNELS …54
A.5.1 Determination of the look through percentage
A.5.2 Using the look through percentage
A.5.3 Influencing the look through percentage
A.5.4 Daytime lighting of short tunnels
A.5.5 A table method for determining the need of artificial daytime lighting
0 Introduction
The aim of tunnel lighting is to ensure that users, both during the day and by night, can approach, pass through,
and exit the tunnel without changing direction or speed with the degree of safety commensurate to that on the
approach road.
To achieve safe passage through a road tunnel, it is necessary that all users have sufficient information regarding
the course of the road ahead, possible obstacles and the presence and actions of other users. Furthermore it is
necessary that users,particularly drivers of motor vehicles, have at least an equal sense of security to that
experienced on the approach roads.
Principal characteristics required to describe the quality of tunnel lighting are:
– the luminance and illuminance levels of the road surface;
– the luminance level of the walls up to 2 m in height above the road surface;
– the uniformity of the luminance distribution on the road and walls;
– the control of induced glare;
– the avoidance of critical flicker frequencies.
1 Scope
This CEN Technical Report gives guidance on the design of the lighting of road tunnels and underpasses for
motorized and mixed traffic. This guidance concerns arrangements, levels and other parameters including daylight,
which are related only to traffic safety. Aspects concerning visual comfort should be chosen in agreement with
national practice. The guidance in this report may be applied to any tunnel or underpass where the decision to
provide lighting has been taken by any authority working within national legislation or other constraints. The report
is based on photometric considerations, and all values of luminance and illuminance are maintained values.
The main body of the report covers the common aspects of Tunnel Lighting, and the various methods currently in
use in Europe are detailed in the annexes. No single method is recommended.
2 References
This Technical reports incorporates by dated or undated reference, provisions from other publications. These
references are cited at the appropriate places in the text and the publications are listed in appendix. For dated
references, subsequent amendments to or revisions of any of these publications apply to this Technical Report only
when incorporated in it by amendment or revision. For undated references the latest edition of the publication
referred to applies.
Not applicable
3 Definitions
For the purposes of this document, the definitions of prEN12665 and prEN13201 and the following apply. The
definitions of zones in a tunnel are based on lighting considerations and not on aspects of installation technique
or on civil engineering. The lighting terms are in agreement with the CIE Publications.
3.1 Tunnel related zones
3.1.1 entrance portal: the part of the tunnel construction that corresponds to the beginning of the covered part of
the tunnel or, when open sun-screens are used, to the beginning of the sun-screens.
he end of the covered part of the tunnel or, when open sun-screens are used, to the end of the
3.1.2 exit portal: t
sun-screens.
3.1.3 access zone: the part of the open road immediately outside (in front of) the tunnel portal, covering the
distance over which an approaching driver should be able to see into the tunnel.
3.1.4 access zone length : the access zone begins at the stopping distance point ahead of the portal and ends
at the portal.
the first part of the tunnel, directly after the portal. The threshold zone begins at the portal.
3.1.5 threshold zone:
3.1.6 transition zone: the part of the tunnel following directly after the threshold zone. The transition zone
stretches from the end of the threshold zone to the beginning of the interior zone. In the transition zone, the lighting
level is decreased from the level at the end of the threshold zone to the level of the interior zone.
3.1.7 entrance zone: the combination of the threshold zone and transition zones.
3.1.8 interior zone: the part of the tunnel following directly after the transition zone. The interior zone stretches
from the end of the transition zone to the beginning of the exit zone.
3.1.9 exit zone: the part of the tunnel where, during day-time, the vision of driver approaching the exit is influenced
predominantly by the brightness outside the tunnel. The exit zone stretches from the end of the interior zone to the
exit portal of the tunnel.
3.1.10 parting zone: the first part of the open road directly after the exit portal of the tunnel. The parting zone is
not a part of the tunnel, but it is closely related to the tunnel lighting. The parting zone begins at the exit portal.
3.2 Lighting
the optical and geometrical means that ensure that motorists are given adequate informa-
3.2.1 visual guidance:
tion on the course of the road in the tunnel.
3.2.2 threshold zone lighting: lighting of the threshold zone of the tunnel which allows drivers to see into the
tunnel whilst in the access zone.
3.2.3 transition zone lighting: lighting of the transition zone which facilitates the drivers' visual adaptation to the
lower level in the interior zone.
lighting of the interior zone of the tunnel which provides adequate visibility in the
3.2.4 interior zone lighting:
interior of the tunnel, irrespective of the use of vehicle headlights.
3.2.5 exit zone lighting: lighting of the exit zone which improves the visual performance during the transition from
the interior zone to the open road beyond the tunnel.
3.2.6 emergency lighting: lighting provided for use when the supply to the normal lighting fails. [prEN 12665]
3.2.7 fire emergency guidance lighting: lighting providing visual guidance in the event of fire and smoke.
3.2.8 daylight screens, louvres: devices that transmit (part of) the ambient daylight. They may be applied for the
lighting of the threshold zone and/or the entrance zone of a tunnel.
screens that are designed in such a fashion that direct sunlight cannot reach the road
3.2.9 sun-tight screens:
surface under the screen.
3.3 Luminances, illuminances
3.3.1 access zone luminance : the eye adaptation luminance in the access zone.
3.3.2 L20 access luminance : average luminance contained in a conical field of view, subtending an angle of
20 ° with the apex at the position of the eye of an approaching driver and aimed at the centre of the tunnel mouth.
L is assessed from a point at a distance equal to the stopping distance from the tunnel portal at the middle of the
relevant carriage-way or traffic lane.
3.3.3 equivalent ocular veiling luminance (Lseq): the light veil as a result of the ocular scatter L is quantified
seq
as a luminance.
3.3.4 atmospheric luminance (Latm): the light veil as a result of the scatter in the atmosphere expressed as a
luminance.
3.3.5 windscreen luminance (Lwinds): the light veil as a result of the scatter in the vehicle windscreen expressed
as a luminance.
3.3.6 threshold zone luminance (L ): the average road surface luminance of a transverse strip at a given
th
location in the threshold zone of the tunnel (as a function of the measurement grid).
the average road surface luminance of a transverse strip at a given location
3.3.7 transition zone luminance (L ):
tr
in the transition zone of the tunnel (as a function of the measurement grid).
3.3.8 interior zone luminance (L ): the average road surface luminance of a transverse strip at a given location
in
in the interior zone of the tunnel (as a function of the measurement grid).
3.3.9 vertical illuminance (E ): the illuminance at a particular location at a height of normally 0,1 m above the
v+
road surface, in a plane facing the direction of oncoming traffic. The height of 0,1 m above the road surface is meant
to represent the centre of an object of 0,2 m x 0,2 m.
3.3.10 contrast revealing coefficient (q ): the quotient between the luminance of the road surface, and the vertical
c
illuminance E at that point.
v+
L
q =
c
E
v
-2 -1
where q is the contrast revealing coefficient in cd.m lx
c
3.3.11 threshold zone luminance ratio (k) at a point: the ratio between the threshold zone luminance L and the
th
access zone luminance L .
L
th
k =
L
3.3.12 overall uniformity (of road surface luminance, wall surface luminance) (U ): ratio of the lowest to the
o
average luminance on the reference field of calculation or measurement.
ratio of the lowest to the
3.3.13 longitudinal uniformity (of road surface luminance of a carriageway) (U ):
l
highest road surface luminance found in a line in the centre along a driving lane. The longitudinal uniformity is
considered for each driving lane.
3.3.14 veiling luminance (Lv): the luminance that, when added by superposition to the luminance of both the
adapting background and the object, makes the luminance threshold or the luminance difference threshold the same
under the two following conditions:
– glare present, but no additional luminance;
– additional luminance present, but no glare.
3.4 Traffic related concepts
that part of the road normally used by vehicular traffic.
3.4.1 carriageway:
a strip of carriageway intended to accommodate a single line of moving vehicles.
3.4.2 traffic lane:
a lane parallel to the traffic lane(s), not destined for normal traffic, but for
3.4.3 emergency lane (hard shoulder):
emergency (police) vehicles and/or for broken-down vehicles.
3.4.4 traffic flow (british) or volume (american): the number of vehicles passing a specific point in a stated time
in stated direction(s). In tunnel design, peak hour traffic, vehicles per hour per lane, will be used.
3.4.5 speed limit: the maximum legally allowed speed.
1)
3.4.6 design speed : a speed adopted for a particular stated purpose in designing a road.
1)
3.4.7 reaction time : the minimum time interval between the occurrence of an event demanding immediate action
by the driver and his response. The reaction time includes th time needed for perception, taking a decision and
acting.
the stopping distance SD is the distance needed to bring a vehicle, driving at design
3.4.8 stopping distance SD:
speed, to a complete standstill. The SD is usually defined in national legislation or regulation. The concept "Safe
stopping distance" is not used in this standard.

1) The terms indicated conform to the "Vocabulary of traffic engineering terms", published by Traffic
Engineering and Control, London, 1960.
3.4.9 mixed traffic: traffic that consists of motor vehicles, cyclists, pedestrians etc.
3.4.10 motor traffic (motorized traffic): traffic that consists of motorized vehicles only. It depends on national
legislation which vehicle types are included in this classification. In some countries it only includes vehicles which
are capable of maintaining a minimum speed. In others, mopeds are not considered as motorized traffic.
Remark concerning traffic flow : if the actual value is not known, peak hour traffic can be derived as follows. Average daily traffic
(ADT, vehicles per day) is the most used concept in traffic planning and it is always known. Peak hour traffic (vehicles per hour) is on
rural areas 10% and in urban areas 12% of ADT. On undivided roads, number of vehicles per hour per lane can be calculated by
dividing peak hour value by the total number of lanes. If the actual directional distribution is not known on dual carriageway roads,
assumption 1:2 can be made. Then the higher flow will be divided by the number of lanes of this carriageway.
4 General aspects of tunnel lighting
4.1 Tunnel conditions
Road and traffic conditions in tunnels may differ considerably from those that prevail on the open road. The design
of tunnel lighting installations should take these different conditions into account, in particular as regards the traffic
safety aspects.
It is desirable to measure tunnel lighting installations after completion to ensure that the design requirements have
been met. Advice on measurement is given in section 9.
4.1.1 Stopping Distance
Important parameters for the design of tunnel lighting installations include the speed, volume and composition of
traffic flow entering, and passing through.
There is a strong, but non-linear relationship between the traffic flow and the accident risk: higher volumes show
a higher accident risk (with the exception of very low or very high traffic volumes). The extra risk can be
counteracted, at least in part, by increasing the light level. This relationship is established for many types of open
roads, and it is assumed that it also holds for tunnels.
One of the most important factor is speed. In practice, road and tunnel designs are such that speed and flow usually
are interrelated, as a high design speed is selected for roads for which a high flow is expected. High speeds require
better visibility and therefore generally a higher luminance level.
The stopping distance SD that often has to be evaluated for the correct design of the lighting is the sum of two
stretches of road:
• the x distance covered during the reaction time
o
• the x distance covered during the braking time
If u is the travelling speed, constant at the beginning of the stopping action,
x = u⋅t (1)
o o
where t is the reaction time.
o
The x distance can be calculated comparing the impulse for a dt time with the momentum












Figure 1: forces acting on a vehicle with different slopes.
⋅ ⋅ ⋅ b6 ⋅ ⋅b⋅ ⋅
- (f m g cos m g sin ) dt = m du (2)
where:
f  =  friction coefficient tire-pavement
m = mass of the vehicle
g  = gravity acceleration
the + sign must be considered for ascending slope; the – sign for descending slope.
=bThe time dt can be expressed as dx/u. Introducing the slope s  tan the (2) becomes:
- cosß⋅g⋅(f6s)dx/u = du or
u
dx du
=-
cosb⋅ g ⋅ f s
()–
Being cosß always close to the unit, it can be neglected.
Integrating the left-hand member between the distance 0 and x, the right-hand member must be integrated between
the speed u and the speed 0. So:
x 0
u
dx =-du
(3)
∫ ∫
g ⋅()–f s
0 u
The integration of the right-hand member is impossible because the friction coefficient f is an unknown function of
the speed and other parameters depending on the speed, such as the atmospheric conditions, the tires condition
and so on.
But assuming f as a constant versus u the (3) gives:
u
(4)
x
=
2 ⋅ g ⋅()–f s





With this hypothesis the formula (4) can be used to determine x if the friction coefficient is assessed by practical
tests and reported in a graph as a function of the speed.
Fig 2: typical diagrams of the friction coefficient as a function of the speed for dry and wet pavement.
Summing the reaction distance (1) and the braking distance (4) the general formula of the stopping distance is
obtained.
u
SD = u ⋅ t +
o
2⋅ g ⋅()–f s
In all the hereabove formulae’s (except in the figure 2 where u is expressed in km/h), u is expressed in m/s, x in m,
t in s and g is equal to 9,81 m.s-2
Without any particular value, t can be assumed equal to 1 sec and f taken from the curve of fig. 2 for wet pavement
o
as a function of the design speed.
4.1.2 Tunnel lighting requirements
The lighting of a tunnel entrance should be adequate:
– to avoid the 'black hole effect' when a driver is unable to see into the tunnel;
– to reduce the likelihood of a collision with another vehicle (or bicycle or pedestrian);
– to enable a driver to react and stop within the SD if an unexpected hazard appears.
4.1.3 Traffic composition
The traffic composition is relevant for the tunnel lighting in several aspects:
– the percentage of trucks;
– the presence/absence of pedal bicycles and/or mopeds;
– the presence/absence of pedestrians (non emergencyconditions);
– the presence/absence of authorization to allow the transit of hazardous material.
The lighting has to be adapted to these circumstances. Higher levels or better quality lighting for the walls or the
road are necessary for the visual task when the conditions are more difficult or more hazardous.
4.1.4 Road and tunnel conditions
Driving comfort is an important aspect of the quality of the lighting installations of road traffic tunnels. Tunnels,
constructed to overcome traffic obstructions, should not become a traffic obstruction by themselves. The design should
be such that the traffic flow in and through the tunnel must be just as fluid as on the open road. As a result of feelings
of anxiety, drivers are likely to slow down near the tunnel entrance. Sudden drops in speed reduce the traffic capacity
and easily might lead to traffic jams and even to accidents. So, a good lighting that helps to overcome any feeling of
anxiety is not only a matter of driving comfort but also a matter of road capacity and of traffic safety.
This may be explained as follows. Driving a car safely is mainly a matter of attention. On long stretches of motorway,
attention may waver and the level of arousal is low. Drivers are not well prepared to cope with emergencies should they
occur unexpectedly. Near tunnels, the attention must be higher to cope with additional hazard factors. Tunnels, being
low and narrow, might cause concern or even fear, but also will lead to an increase in arousal. The fear and the arousal
are likely to cancel out each other to a large extent, so that the more dangerous tunnel entrance need not to lead to
more accidents. However, what happens to the driving comfort is another matter.
The object of installing lighting in a road tunnel is to enable the traffic to pass through with the same degree of
safety and comfort, as is customary on the open road, and with an acceptable speed. The difficulty of the driving
task when approaching and passing through a tunnel is mainly 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. To enable
a road user to drive safely when a tunnel is on his route, it is pertinent to give him adequate and relevant
information, which allows the driver to situate himself in space and time, to foresee a "model" of his future position
and to adapt his behaviour to this anticipated "model".
When making the lighting design for a tunnel, the following aspects should be taken into account:
a) Altered perception
The spatial perception is confined and cut off from any familiar reference marks. The walls may generate a "wall
shyness effect" which tends to make drivers keep further away. Drivers' visual performance may be considerably
lower, especially regarding visual acuity, the perception of contrast and distances, peripheral vision and the
discrimination of colours. Time perception may change: the perceived duration seems to be about twice as long as
the actual time span. And finally, some drivers can be affected by sensations such as claustrophobia.
b) Overall perception
1. Before entering a tunnel
– the layout should clearly show that one is approaching a tunnel - this should be supported by relevant signs;
– portals should be constructed with dark materials in order to reduce the access zone luminance;
– there should be a black asphalt surface for the road up to the portal.
2. Entering the tunnel
– East-West orientations may cause more problems than North-South orientations;
– avoid light coloured surfaces in the immediate surround of the portal such as buildings, walls, etc.;
– adopt trees or other screens to avoid direct glare from the sun.
3. Inside the tunnel
– if discontinuities, ramps and intersections in the geometric design, it is advised to treat them specifically by
an ad hoc lighting system;
– adopt a light coloured road surface that should be near diffuse for symmetric lighting and more specular for
counterbeam lighting;
– adopt and maintain good guiding facilities (road markings, delineators etc.) along the road;
– adopt separate sign lighting when the tunnel is lit by monochromatic light-sources.
4. At the exit
– adopt, when a glaring situation may be expected outside the exit, civil engineering works or planting that will
screen off the direct sunlight.
4.2 Distinction between long and short tunnels
The lighting requirements for long and short tunnels differ according to the degree to which the approaching motorist
can see through the tunnel as seen from a point at a distance equal to the stopping distance in front of the tunnel
portal. The ability to see through the tunnel depends primarily on the length of the tunnel but also on other design
parameters (width, height, horizontal and/or vertical curvatures, etc).
Short tunnels normally occur when a traffic road passes under another road or railway or are covered over for a
short distance in urban situations. Tunnels shorter than 25m do not need daytime lighting. Tunnels longer than
200m always need some kind of artificial daytime lighting to avoid adaptation problems for road users. For tunnels
of length between 25m and 200m, a method to determine if daytime lighting is needed is given in Annex A5. Another
method produced by the CETU may be found in the following reference (Cetu Dossier pilote des tunnels; Novembre
2000; Centre d‘Etude des tunnels ; Bron, France).
The need for artificial lighting during day-time is determined by the degree in which other road users or objects are
visible for a driver in front of the entrance at stopping distance against the scene behind the exit which is lit by the
daylight.
When the exit portal is a large part of the scene visible through the entrance other road users and objects can easily
been seen as dark against the lighter scene behind the exit portal. At the other hand artificial lighting is needed
when the exit is in a relative large dark frame, in which objects can be hidden. This can happen when the short
tunnel is relatively "long", or when the short tunnel is curved in such a way that only a part of the exit can be seen
or when the exit cannot be seen at all.
So the critical factor is whether approaching drivers when their distance from the entrance portal is equal to the
stopping distance can see vehicles, other road users or obstacles.
For determining the need of artificial daytime lighting the "Look Through" is used.
The "Look Through" is defined as the ratio between the visible exit and the visible entrance, expressed as a
percentage. This leads to the "Look Through Percentage" (LTP):
The ratio is based on:
• geometrical measures of the tunnel as width, height, and length (the length has much more influence as the
width and height)
• horizontal and vertical curves of the tunnel
• the stopping distance
• the influence of day-light at both the entrance and exit portal

Fig 3:view of a short tunnel
4.3 Lighting systems and contrast rendition methods
4.3.1 Artificial lighting systems
The contrasts of objects can be negative or positive, depending on the reflection properties of the surface of the
object and on the lighting system used. There are two artificial lighting systems in common use : the symmetrical
lighting system and the counterbeam lighting system. Pro-beam lighting is seldom used and will not be described
in this report. The symmetrical and counterbeam terms refer to the luminous intensity distribution of the luminaires
that are used for the two systems. The symmetrical system is a system where the luminaires show a luminous
intensity distribution that is symmetrical in relation to the 90°/270° C-plane (the plane usually normal to the direction
of the traffic). In a counterbeam lighting system luminaires are applied where the maximum luminous intensity is
aimed against the direction of the traffic and with a low luminous intensity in the direction of the traffic so that the
luminous intensity distribution is strongly asymmetric. The terms refer only to the direction of normal traffic.
The luminous intensity distribution is not sufficient to quantify the effect of the installation, because the effect of the
lighting is determined by the contrasts. The effect of the lighting is characterized by the value of the contrast
revealing coefficient q . CBL systems should have a value of L/E above 0,6.
c v
Fig 4:counterbeam lighting system
Fig 5:symmetrical lighting system
The counterbeam lighting system comprises luminaires with a luminous intensity distribution that is aimed against
the direction of the traffic. It usually produces a higher negative contrast for objects on the road, because the
illuminance on the planes that are facing the approaching drivers is low. When specular road surfaces are used (R3,
R4, C2, see CIE publication 66), the luminance yield usually is significantly higher than with symmetrical lighting.
The counterbeam system will normally create greater contrast between objects and the background (e.g. road
surfaces and walls).
However, the counterbeam system:
– may give some increase in the "black hole" effect, because in some design methods the threshold luminance
may be lowered, so that drivers' guidance may be reduced;
– may not be appropriate for a tunnel entrance with high daylight penetration;
– may prove to be less effective for tunnels with very high traffic flows or for tunnels with a high percentage of
heavy goods vehicles;
– may be less effective in revealing road markings that show a diffuse reflection.
4.3.2 Screened daylight systems
Daylight, controlled by screens, may be used as an alternative light source for tunnel entrances. As regards the
luminance and illuminance levels, the daylight has to comply with the same minimum requirements as the artificial
light. It is recommended, however, that the road surface luminance under the screens is higher than would
correspond to these minimum requirements. This recommendation holds for the different tunnel lighting design
methods described in this report. The Contrast Revealing Coefficient q should be determined in the same way as
C
for artificial light. Daylight screens may be sun-tight or non-sun-tight. Sun-tight screens over the roadway serve to
realize the threshold zone luminance and sometimes part of the transition zone luminance in much the same way
as artificial lighting. Non-sun-tight screens over the roadway serve primarily to screen the bright sky directly over
the tunnel entrance from direct view. Non-sun-tight screens may cause unwanted flicker effects (see 4.4.1). When
open daylight screens are used in situations where heavy snowfall is common, provision must be made to avoid large
blocks of snow falling on the road below the screen.
4.4 Aspects common to various design methods
4.4.1 Flicker
Flicker sensations are experienced when driving through spatially periodic changes in luminance, such as those
produced by louvres in the tunnel walls or ceiling, or by incorrectly spaced luminaires (with high rate of change in
their luminous intensity distribution). The visual discomfort experienced due to flicker depends upon:
A) the number of luminance changes per second (flicker frequency);
B) the total duration of the flicker experience;
C) the rate of change from light to dark in a single cycle;
D) the ratio of peak (light) to trough (dark) luminance within each period (luminance modulation depth).
The influences of points (a), (b) and (c) depend upon vehicle speed and luminaire spacing; points (c) and (d)
depend also on the optical characteristics and spacing of the luminaires.
When the distance between the ends of adjacent luminaires is less than the length of the flashed area of a single
luminaire, the fourth point (d) is typically minimised and perceived flicker rendered negligible - at least with respect
to the artificial lighting.
To calculate the flicker frequency within a stretch of tunnel, divide the velocity (m/s) by the luminaire spacing (m).
For example:
If velocity = 60 km/h = 16,6 m/s and luminaire spacing = 4 m,
then Flicker frequency = 16,6/4 » 4,2 Hz.
In general, the flicker effect is negligible at frequencies below 2,5 Hz and above 15 Hz. When the frequency is
between 4 Hz and 11 Hz, and has a duration of more than 20s., discomfort may arise provided no other measures
are taken.
The lengthwise interdistance between consecutive luminaires for compact light sources with a high gradient in the
luminous intensity distribution (eg high pressure sodium lamps with optical systems) should be such that
frequencies of luminance variation between 2,5 Hz and 15 Hz occurring at the design speed, and over a duration
of more than 20 s are avoided. This value is valid for all tunnel zones, including non-suntight daylight louvres at the
entrance and/or the exit. For large size luminaires with low gradients in the luminous intensity distribution the
requirements to restrict flicker effect are less stringent. For daylight louvres that are non sun-tight, the frequency
of luminance variation should be always higher than 50 Hz, independent of the distance covered by the louvres.
4.4.2 Glare restriction
As glare reduces visibility, it is important to minimize it. In tunnel lighting the physiological (disability) glare has to
be considered. Disability glare effects are quantified by the Threshold Increment TI as described in "Glare and
Uniformity in Street lighting" CIE Publication No. 31,1976.
During day-time the threshold increment TI must be less than 15% for the threshold zone, and the interior zone of
the tunnel, and for all tunnel zones during the night. For the exit zone during day-time no restriction is given. The
following formula shall be used to calculate TI:
0,8
TI = 65 / if  < 5 cd/
m
Lv Lroad Lroad
1,05 2
TI = 95 / if  ‡ 5 cd/
L L L m
v road road
With L : average road surface luminance
road
And L : veiling luminance created by all luminaires in the field of view where the axis of fixation is 1° down from
v
the horizontal at the relevant location. The calculations shall be made on the base of the initial values and with a
full cut-off angle of 20° above the axis of observation due to the roof of the car.
4.4.3 Lighting control
The access zone luminance varies with changes in day-light conditions. During the day, the luminance levels in the
threshold and transition zones need to be constant percentages of the luminance in the access zone. Therefore,
it is necessary to provide automatic control of the artificial lighting in these zones. Two systems are possible:
switching off (or on) groups of lamps, or dimming them. The first is the most commonly applied, particularly at high
luminance levels.
For the automatic control, the most practicable solution is to place a luminance meter with a measuring field of 20°,
centered on the tunnel portal and positioned at the stopping distance (SD) in front of the tunnel portal. For practical
reasons, the luminance meter usually has to be mounted at a greater height than the driver's eye position. Therefore
the instrument has to be calibrated separately at the correct position.
The switching of lamps may be done in steps to switch various lamps on or off. This switch should have a time delay
of several minutes to avoid unnecessary switching owing to transient variation in the local lighting level caused by
passing clouds.
Dimming can be considered but the actual saving must be taken into account. Studies have shown that dimming
can result in considerable financial savings. The increased equipment cost and sometimes the lowering of the lamp
efficacy (lm/W) must be taken into account.
Maintaining and cleaning of the control equipment should be done frequently.
4.4.4 Maintenance
In order to maintain the design performance of the lighting installation cleaning is particularly important and walls
and luminaires should be washed frequently. The actual cleaning cycle should be related to the maintenance factor
used in the calculations of the lighting levels.
The maintenance factor refers to the depreciation in the photometric performance of a luminaire from its state when
new to its worst acceptable state in service. At the design stage, a factor of 0,7 is recommended for the
maintenance factor in calculating luminance (and illuminances) on the road. This factor applies to the luminaire only.
Lamp output depreciation is accounted for by use of the lamp lumen maintenance factor in the calculation. The
initial values should be related to 100 h of use. In practice the luminance of the walls will decrease faster than that
of the road surface because both the luminaire output and the reflection factor of the walls will decrease. This can
be allowed for at the design stage by assigning a maintenance factor to the wall reflectance, approximately equal
to that applied to the luminaire output. Thus the effective maintenance factor used in the calculation of wall
luminance is the square of the recommended value of 0,7 i.e. about 0,5. This means that the road luminance in the
tunnel should not drop below 0,7 of its initial value and the cleaning cycle should be arranged to ensure that this
is the case. The relamping cycle should be monitored in order that the maintenance factor does not fall below 0,7,
or that failed lamps give unacceptable uniformity.
5. Lighting of long tunnels
It is essential to know the luminance in the access zone in order to determine the luminance levels that are required
in the entrance zone of the tunnel. Alternative methods of assessing the access zone luminance are given in
annexes A1 to A4. The value of the access zone luminance that is used for the lighting design and/or the lighting
control should be determined in one of two ways: it is either the maximum access zone luminance occuring during
the year, or it is that value which is only exceeded for a certain proportion of a year decided by national agreement.
a. The L20 method is described in Annex A1. It covers daytime lighting of the threshold, transition and interior
zones and nighttime lighting of the whole tunnel.
b. A traffic-weighted adaptation of the L20 method is described in Annex A2. It classifies tunnels into classes,

using parameters related to the traffic and visual conditions. It covers daytime lighting of the threshold,
transition, interior and exit zones, with guidance on the parting zone where appropriate and nighttime lighting
of the whole tunnel.
c. An alternative method of assessing the luminance of the threshold and entrance zones is provided in Annex

A3, using the veiling luminance Lv.
d. A further method of assessing adaptation luminance is described in Annex A4.
6. Artificial lighting of short tunnels and underpasses
When artificial daytime lighting is needed, the lighting should comply with the requirements of long tunnels. Part-
time daytime lighting is provided during periods when the daylight penetration does not provide a background of
sufficiently high luminance to enable the silhouette effect to operate. Such conditions may arise after dawn, prior
to dusk and on overcast days.
For short tunnels longer than 25 m where the approach roads are lit, night-time lighting is recommended even if
there is no justification for daytime lighting. The luminance should be at least equal to, but not more than twice that
of the approach roads.
7. Emergency lighting
In the event of a failure in the normal power source that supplies the lighting system, it is recommended that an
emergency uninterruptible power supply is employed to energise sufficient system luminaires to allow users to exit
the tunnel in safety. Conventionally, the emergency luminaires form part of stage 1 of the normal tunnel lighting
system, stage 1 being the normal night time level throughout the tunnel. The emergency configuration by example
could consist of : -one lamp from a selection of the system luminaires, forming a linear symmetrical and interspaced
series of emergency luminaires, being energised from the uninterruptible power supply source. It is recommended
that the average illuminance level of the emergency lighting should be at least 10 lux with 2 lux being the minimum
level at any location within the tunnel. For recommendations relating to escape lighting in the event of fire,
appropriate references and standards should be sought by te reader (e.g : CETU guide on tunnel lighting and EN
1838).
8. Traffic signals
When Sodium Vapour Lamps (both high and low pressure) are used for lighting, the spacing between the luminaires
and yellow traffic signals should be either a horizontal distance of at least 1 m, or an angular separation of at least
1 ° (whichever is higher), observed from a distance equal to 50 % of the SD.
9. Measurement
of tunnel lighting installations
9.1 Quality numbers for tunnel lighting installations
To describe quantitatively the performance of a tunnel lighting installation, the following performanc
...