ROAD TUNNELS GEOMETRIC DESIGN

4 Geometric design

401 General same road with corresponding traffic

Tunnels are distinguished from open roads type and volume.
in respect of conditions such as: The demands placed on standards increase
correspondingly with traffic volume and
• little or no lateral movement tunnel length. Tunnels are therefore placed
• other winter conditions in categories which determine the required
• regular lighting throughout the day and geometric specifications and features.
year, except from the entry zone
• difficulties in estimating gradients 402 Selection of tunnel category
• difficulties in estimating distance to The traffic volume is normally given in
vehicle in front AADT (Annual Average Daily Traffic vol-
• other safety measures, breakdown ume). AADT is the total annual traffic
services, etc. divided by 365 and is given as the total
These require that a number of design ele- traffic volume in both directions.
ments will differ to those of the open road. The tunnel category is determined
Maintenance and operations shall ensure according to the estimated traffic volume
a constant level of safety in the tunnel. twenty years after opening, AADT(20).
Where the traffic volume varies
Important elements in this connection are: throughout the day or over the year, or
• selection of the appropriate construc where there is considerable uncertainty in
tion method and equipment in the plan calculating AADT(20), the tunnel catego-
ning and construction phases ry may be based on selected criteria. The
• uniform standard for tunnels along the chosen category must be approved by the

Average annual
daily traffic AADT F 2 x T 9.5
15000

E 2 x T 8.5 (2 x T9.5*)

10000
Special evaluation

D T 9.5
7500
C T 8.5 (T9.5*)
5000

B T 8.5

A T 5.5
300

0.5 2.5 5.0 7.5 10.0 12.5

Figure 4.1 Tunnel categories. T9.5*
applies to trunk road network Tunnel length in kilometres

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 ROAD TUNNELS GEOMETRIC DESIGN

Directorate of Public Roads. must be allowed facilitating construction

The tunnel categories are based upon traf- of this second tube at a later point in time.
fic volume and tunnel length. (See Figure If construction of tunnel tube number
4.1) The tunnel categories are the basis for two is deferred, this may necessitate con-
a specific cross-section, number of traffic struction of an overtaking lane in accor-
lanes, need for emergency lay-bys and dance with section 412.5 “Overtaking
turning points together with safety equip- lanes”.
ment. The latter is described in more detail
403 Tunnel cross-sections
in Chapter 6, “Traffic and Fire Safety”.
The tunnel cross-sections are designated
Figure 4.1 applies to tunnels longer than
according to the total width of the road
500 m. Initially, the cross-section is also
surface. (See Figure 4.2).
selected according to this figure for short-
er tunnels except that the width of the The cross-section of Tunnel T4 has ver-
shoulder at the open road may be extend- tical walls.
ed throughout the tunnel. Tunnel cross-sections T5.5 – T12.5
Tunnels with a single lane (AADT< 300 have a circular contour above the road sur-
on county roads) are defined as Tunnel face.
Category A. The cross-section of these The vertical clearance requirements in
tunnels is shown in Figure 4.4. tunnels is 4.6 m except for pedestrian and
Tunnels on trunk roads in Categories C cycle tunnels. The vertical clearance spec-
and E shall be constructed with tunnel ifications apply to the vertical distance
cross-section 9.5 measured on the carriageway boundary.
If traffic volume AADT(20) prescribes Normal cross-sections will be in excess
tunnel Category E, a decision of when to of this to allow for:
construct the second tube shall be made. • extra clearance for subsequent road
Where this is deferred, circumstances resurfacing

Centre line Tunnel

Profile line

Standard cross section

Theoretical excavated cross-section

Reserved for support measures

Traffic zone
Pavement structure

Carriageway boundary

Theoretical drainage
Formation level trench cross-section

Verge
area Carriageway width Shoulder

Figure 4.2 Tunnel cross-section

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 ROAD TUNNELS GEOMETRIC DESIGN

. . .

Figur 4.3 Tunnel cross-section T4 (measured in metres) T4 is used for pedestrian and cycle paths.
Stipulated clearance height is 3 m. This cross-section is also used for footway interconnections in tunnels
with two tubes (Tunnel categories E and F)

.
. . .

Figure 4.4 Tunnel cross-section T5.5 (measured in metres)T5.5 is used for sliproads with a single lane
without requirements that a broken-down vehicle may be passed. T5.5 is also used for single lane roads
with meeting points in Tunnel category A. Vertical walls may be an alternative in single-lane tunnels.

33
 ROAD TUNNELS GEOMETRIC DESIGN

. .
. . . .

Figure 4.5 Tunnel cross-section T7 (measured in metres).T7 shall be used for slip roads on a single lane
with possibilities for a broken-down vehicle to be passed. The carriageway is marked as a driving line
width 3.5 m, and an emergency lane width 1.5 m. The emergency lane is included in the extended bre-
adth in order to ensure vision requirements.

. .
. . . .

Figure 4.6 Tunnel cross-section T8.5 (measured in metres) T8.5 is used for tunnels with two-way traffic
in tunnel categories B and C, and for each tube in Tunnel category E.

34
 ROAD TUNNELS GEOMETRIC DESIGN

. .
. . . .

Figure 4.7 Tunnel cross-section T9.5 (measured in metres). T9.5 is used for tunnels with two-way traffic
in tunnel category D, and for each tube in tunnel category F together with tunnel categories C and E on
the trunk road network.

. .
. . . . .

Figure 4.8 Tunnel cross-section T11.5 (measured in metres) T11.5 is used where there is a requirement
for three lanes or an emergency lay-by in tunnel categories B,C and E. The cross-sections also provides
room for two lanes and a separate pedestrian and cycle path seperated with concrete guardrail. (see
Figure 4.16). The figure shows normal lane partitioning with an emergency lay-by. In other situations the
lane partitioning must be considered in the light of the local traffic situation.

35
 ROAD TUNNELS GEOMETRIC DESIGN

. .
. . . . .

Figure 4.9 Tunnel cross-section T12.5 (measured in metres) T12.5 is used where there is a requirement
for 3 lanes or emergency lay-by in tunnel categories D and F. The figure shows the normal partitioning
with an emergency lay-by. In other situations the lane partitioning must be considered in the light of the
local traffic situation.

• normal tolerance for tunnel linings, the carriageway. For laterally-mounted

water and frost protection / concrete equipment such as traffic signs etc., the
linings (total deviation = 0.1 m) clearance must be individually deter-
• requirements for vertical clearance mined. With consideration to emergency
including kerbstone. exits laterally mounted signs should be
Normally the tunnel cross-section will placed such that the minimum height
also include space for traffic signs and below the sign is at least 2.0 m.
technical installations. The need for extra Requirements of signs are discussed in
width locally must be considered in each Section 414.
individual case. The minimum height for
technical equipment must be 4.8 m above

Table 4.1 Geometric specification for the various tunnel cross-sections

Total Carriage- Centre point Centre height Wall radius Centre height Lining
Cross- width way width wall radius wall radius lining radius radius
section BT BK X YV RV YH RH

T4 4.0 3.0 - - - 1.33 2.40

T5.5 5.5 3.5 3.40 1.77 4.79 3.17 2.59
T7 7.0 5.0 2.06 1.57 4.79 2.78 3.20
T8.5 8.5 6.5 0.40 1.77 4.79 1.98 4.50
T9.5 9.5 7.0 0.44 1.57 4.79 1.22 5.20
T11.5 11.5 9.5 2.60 1.77 4.79 - 0.26 7.20
T12.5 12.5 10.0 3.44 1.57 4.79 - 0.46 7.45

All measurements in metres

36
 ROAD TUNNELS GEOMETRIC DESIGN

Centre line
Vertical clearance 4.60m

x x
2 2

Verge Verge
area Carriageway width BK area

Total width BT

Figure 4.10 Geometric measurements for tunnel cross-sections categories T4 -T8.5 (measurements are
given in Table 4.1).
Centre line
Vertical clearance 4,60m

x x
2 2

Verge Verge
area Carriageway width BK area

Total width BT

Figure 4.11 Geometric measurements for tunnel cross-sections categories T9.5 - T12.5 (measurements
are given in Table 4.1).

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 ROAD TUNNELS GEOMETRIC DESIGN

Table 4.2 Cross-section data for the various tunnel cross-sections

Theoretical excavated cross-section Normal cross-section

Tunnel cross-section Area AS Arc length, BS Area AN Arc length, BN
m2 m m2 m

T4 20.31 12.31 13.65 10.04

T5.5 39.11 17.12 28.77 14.90
T7 47.85 18.32 37.23 16.01
T8.5 61.92 20.56 49.66 18.24
T9.5 66.53 21.02 53.53 18.71
T11.5 85.95 23.76 70.89 21.43
T12.5 91.23 24.30 75.41 21.99

Specifications will be dependent upon the pavement construction and area reserved for lining. The following specifications apply to the table:
AS = Area calculated on a theoretical excavation cross-section. The pavement has been determined at 0.5 m and lining at 0.4 m in the
table.
AN = Calculated area of a normal cross-section above the carriageway and verge area assuming a 5% decline on the shoulder
BS = Calculated arc length based on a theoretical excavation cross-section down to the formation level assuming 0.5 m for the pavement
and 0.4 m for lining.
BN = Calculated area of a normal cross-section down to the level for the carriageway

Geometric measurements In the entry zones where the environ-

The geometric specifications are given in mental impact is particularly large, shoul-
Table 4.1 and illustrated in Figures 4.10 ders shall always have a concrete surface
and 4.11 in tunnel categories C, D, E and F.
The cross-section data of the tunnel Shoulders in these zones with a concrete
cross-section are given under the assump- surface should extend a minimum of 200
tions made in Table 4.2 and Figure 4.2. m into the tunnel at each end.
The tables also apply to tunnel cross-
sections with a unilateral cross-fall. In this
405 Safety measures with dangerous
event the cross-section pivots on the cen-
side obstacles
tre carriageway. The tables are thus inde-
Cushions should be used along slip roads
pendent of the degree of the cross-fall.
and other structures which may comprise
Standard cambers are not normally used
dangerous side obstacles.
in tunnels.
The ends of the linings shall be designed
404 Verge area to take safety into consideration. This is
The verge area refers to the area outside done using a slope (1:10) for a minimum
the marked driving lane. of 0.9 m above the carriageway.
The shoulder should be bordered with
kerbstones and constructed of asphalt or 406 Construction below the carriage-
concrete with a minimum decline of 5% way level.
towards the carriageway. The kerbstones The formation level (the theoretical exca-
should be low with an obtuse face (lip vation cross-section) is determined by the
kerbs) placed 0.25 m from the edge of the thickness of the pavement. The formation
carriageway. (See Figure 4.2). below the carriageway level is otherwise

38
 ROAD TUNNELS GEOMETRIC DESIGN

determined by drainage trenches, cable might suggest a deviation from the nor-
ducts, and so forth. mal tunnel cross-section include:
The excavated base shall have an incli- • The need for a shallow tunnel course.
nation corresponding to that of the pave- The tunnel roof is formed parallel to
ment. the carriageway while the circular
See also Chapter 8 and Chapter 9 cross-section is retained for the walls
• When it is desirable that the breadth of
407 The tunnel cross-section for the building site is reduced
concrete tunnels • For tunnels where the design is deter-
The choice of tunnel cross-section is mined by water pressure, a square
determined following a comprehensive profile has a lower volume and conse
technical/economic evaluation. The main quently less buoyancy.
rule is that the ordinary tunnel cross-sec- If it is necessary to reduce the height of a
tions will apply unless special circum- concrete tunnel, the technical equipment
stances determine otherwise. and signs can be placed in the side areas.
Examples of circumstances which This may then require the shoulder area to
be increased.

Figure 4.12 Emergency lay-by

Figure 4.13 Turning point

39
 ROAD TUNNELS GEOMETRIC DESIGN

Figure 4.14 Example of a turning point for a snowplough.

408 Extension for lay-bys and niches be located together with the emergency
lay-bys. See Section 408.2.
408.1 Design and location of emergency In long tunnels, special turning points
lay-bys and turning points for snow ploughs are required. An exam-
Emergency lay-bys enable parking outside ple of the design is given in Figure 4.14
of the carriageway in the case of emer- The distance between the lay-bys is
gency. Emergency lay-bys are designed as determined by the tunnel category. The
in Figure 4.12. The tunnel cross-sections distances given are approximate. The loca-
in emergency lay-bys are shown in tion will depend upon the local circum-
Figures 4.8 and 4.9. stances including rock mechanics and geo-
Turning points are built into two-way metric considerations. Further, considera-
tunnels. Emergency lay-bys can also func- tion must be made to designing niches for
tion as turning points for light vehicles. several purposes (for example, technical
Turning points for heavy vehicles are room, pump station etc.). Deviations in
designed as in Figure 4.13. location should be within ±50 m for emer-
Technical equipment is located in sepa- gency lay-bys and ±100 m for turning
rate niches with an enclosing wall along points.
side the traffic lane. These niches should

Table 4.3 Normal distances between lay-bys

Tunnel Normal distance Normal distance Comments

category emergency lay-bays turning points

A - - See Section 410 for meeting points

B 500 m 2 000 m
C 375 m 1 500 m
D 250 m 1 000 m
E, F 500 m - The given distances for tunnel categories E
and F apply to each of the tunnels tubes

40
 ROAD TUNNELS GEOMETRIC DESIGN

Figur 4.15 Niche for technical equipment

The normal distance between lay-bys is an extra overtaking lane is constructed

shown in Table 4.3. Examples of location (see Section 412.5).
are given in Chapter 6 “Traffic and fire
safety”. 408.2 Niches for technical equipment
For Tunnels in Category A, single lane Technical equipment must be located in a
tunnels, see section 410. separate niche, preferably linked to an
The first emergency lay-by shall be emergency lay-by and separated by a
located not less than 250 m from the tun- sealed off wall from the traffic lanes
nel entrance. (Figure 4.15). Regulations for cooling
When preparing a lay-by plan the fol- require that the technical equipment niche
lowing additional considerations must be shall be constructed in concrete.
made regarding the number of lay-bys and Where the niche is located away from an
their location: emergency lay-by, a separate parking lay-
• Normally, lay-bys should not be situat by must be constructed. The design for
ed on an inside curve with regard to vis this is illustrated in Figure 4.15.
ibility for approaching vehicles
• At a junction in the tunnel, the start 408.3 Extension in mountain tunnels
and the end of the slip roads is consid with convoy traffic
ered as an emergency lay-by area In tunnels with periodic closures on
• In tunnels where the AADT(20) <2500 account of convoy traffic for example,
and the gradient >6% over a length of consideration should be given to increas-
1 km, consideration should be given ing the width in order to increase the safe-
to an extra emergency lay-by for every ty factor with convoy formation.
kilometre of the incline.
If the AADT(20) is >2500 in tunnels 409 Interconnections
with two-way traffic, the need for an Where two parallel tunnel tubes have been
extra lay-by is catered for in so far as constructed, interconnections linking the

41
 ROAD TUNNELS GEOMETRIC DESIGN

Figure 4.16 Pedestrian and cycle paths in a two-lane tunnel, tunnel cross-section T11.5

two tunnels shall be constructed at inter- fic be permitted in tunnels longer than 4
vals of 250 m. km. There are special requirements for
The footway interconnections shall be lighting and ventilation for these tunnels,
constructed using tunnel cross-section T4. as described in Chapter 10 “Technical
Further information is given in Chapter equipment”
6 “Traffic and fire safety”.
The pedestrian and cycling area is locat-
410 Single lane tunnels ed on one side of the tunnel, having a min-
In single lane tunnels used by traffic in imum breadth of 2.0 m and a minimum
both directions meeting points have to be height of 3.0 m. A concrete safety barrier
constructed. Distance between meeting- separates pedestrian/cycle traffic from
points should be 250 m, but never longer automobile traffic.
than that a driver can see ahead to the Tunnel cross-section T11.5 is designed
next meeting point. Meeting points shall to permit the construction of a pedestri-
be designed as emergency lay-bys. See an/cycle way separated from the two-lane
Figure 4.12. carriageway by a concrete safety barrier
(Figure 4.16). In special circumstances the
411 Pedestrians and cyclists Directorate of Public Roads can permit
Under certain circumstances it may be pedestrian and cycle traffic in tunnels with
necessary to permit pedestrian and cycle other cross-sections, and without a con-
traffic in tunnels where no alternative crete barrier. One solution can be a foot-
route exists. Only in exceptional circum- way with a high kerbstone combined with
stances should pedestrian and cycle traf- a low speed limit.
Where pedestrian and cycle traffic pro-

42
 ROAD TUNNELS GEOMETRIC DESIGN

Figure 4.17 Line of sight in a tunnel

ceed in a separate tunnels cross-section T4 prevent overtaking and to avoid daylight

is used. in the openings complicating the lighting
conditions for motorists. In tunnels longer
412 Alignment than 6 km gentle curves may be designed
412.1 General to counteract monotony.
Alignment specifications in a tunnel differ The horizontal curve diameter is con-
from those of a normal highway on stant within 2/3 of the stopping sight dis-
account of different driving conditions. tance within the tunnel entrance and the
Trunk roads employ a different align- approach section. It is particularly impor-
ment theory which may permit some devi- tant to avoid a transition from a curve to a
ation to that described below. straight section within the immediate tun-
Both the under-mentioned and trunk nel entrance.
road norms can be used in the design. The requirements of the stopping sight
distances will determine the sharpest hori-
412.2 Design speeds zontal curve. (See Table 4.4).
In tunnels the radius of the sharpest hori- Where it is desirable or necessary that
zontal curve is determined by the viewing the horizontal radius is less than that
distance. Thus, based on dynamic consid- required by the stopping sight distance,
erations it is possible to drive faster than the width of the inner curve must be
the speed for which the tunnel is designed. increased.
If the tunnel exceeds 2.5 km the design The association between the horizontal
speed should be at least 80 km/h. curve radius (R), the length of sight (stop-
If the gradient is 6% or steeper for at ping distance) (LS) and distance as viewed
least 1 km, the design speed should be at from the driver’s eye to the tunnel wall (B)
least 80 km/h. is given by the formula:
For shorter tunnels and tunnels in urban R = LS2 / 8B [m]
areas the design speed may be determined
by the neighbouring road system of which See Figure 4.17, Table 4.4 and Figure
the tunnel forms a part. 16.25 in Manual 017 for further specifica-
tions.
412.3 Horizontal curves/view I two-way tunnels the eye is considered
A curve should be considered as part of to lie 1.1 m above the carriageway and 1 m
the approach at each end of the tunnel to from the centre line.

43
 ROAD TUNNELS GEOMETRIC DESIGN

Table 4.4 Stopping sight distances (LS) in metres for different incline gradients, AADT and design speeds

Design. AADT(20) 0 - 1 500 AADT (20) 1 500 - 5 000 AADT(20) > 5 000
speed gradient s gradient s gradient s
km/h
≥ -8 % -7 - +7 % ≥8% ≥ -8 % -7 - +7 % ≥8% ≥ -8 % -7 - +7 % ≥8%

50 55 49 41 59 57 47 64 54 49
60 72 64 58 79 68 61 88 73 64
70 94 82 74 109 87 77 116 94 82
80 119 102 91 131 109 96 149 119 102
90 146 124 110 164 134 116 189 147 124
100 178 149 131 201 162 139 234 178 149
110 215 177 154 244 193 165 288 215 177
120 255 208 180 293 229 193 350 255 208

In left-handed curves in one-way tun- The AADT values in Table 4.5 apply to
nels, the eye distance is considered to lie 1 road stretches with a normal traffic distri-
m from the carriageway boundary. bution throughout the year and where the
The specifications for lane widening are proportion of heavy vehicles throughout
the same as for open roads. the year is 10-15%.
Widening is carried out on the inside In suburban areas with typical rush-hour
lane and does not change the radius of traffic where the proportion of heavy vehi-
the tunnel wall. cles is < 7%, the AADT values in the table
may be increased by 25%.
412.4 Vertical curves
The maximum incline for tunnels is shown 412.5 Overtaking lanes
in Table 4.5. With regard to the general norms for over-
Where an overtaking lane is constructed, taking possibilities along each 5 km road
the values in the table may be increased by stretch, measures will often be required in
1%. tunnels to facilitate overtaking.
Tunnels with local characteristics and Opportunities for overtaking require that
low traffic volume, together with urban the line of sigth is sufficient, or that an
tunnels outside the main road network, extra lane is constructed.
may be constructed with a gradient of up The need for an overtaking lane is based
to 10%. It is necessary to have this ratified upon estimated capacity.
by the Directorate of Public Roads. In tunnels with two-way traffic and a
The AADT values for one-way traffic in gradient of > 6% over a stretch exceeding
Table 4.5 apply to both tunnel tubes in 1 km, a separate overtaking lane shall be
aggregate. constructed when the AADT(20) is > 2500.

Table 4.5 Permitted gradients for tunnel

Two-way traffic One-way traffic

AADT (20) 0 - 1 500 > 1 500 < 15 000 > 15 000

Max.gradient 8% 7% 7% 6%

44
 ROAD TUNNELS GEOMETRIC DESIGN

Table 4.6 MInimum permitted vertical radius (m) in dips

Design speed (km/h)

30 40 50 60 70 80 90 100
Standard class

H1, S1 240 420 650 930 1270 1650 2090 2580

H2, S2 140 250 390 560 760 990 1250 1550

H3, S3, A1 100 180 280 400 550 710 900 1110

The lane commences latest at that point ority, normal intersections (X-junction and
where the difference in speed of heavy T-junction) should not be located closer to
vehicles and light vehicles is 15 km/h or the tunnel entrance than 2 x the stopping
greater, and should be at least 1 km in sight distance (LS). With good visibility
length. and satisfactory advance warning of the
In tunnels where overtaking possibilities junction, the distance may be reduced
have to be ensured with an adequate line somewhat, but not less than 1.5 x the stop-
of sight, it is preferable to construct long ping sight distance.
straight stretches rather than long curves When traffic exiting the tunnel has the
with large radii. This also applies to tun- obligation to give way or is controlled by
nels with an overtaking lane in long gradi- traffic lights, the distance from the tunnel
ents to give the possibility for overtaking opening to the give-way line, stop line or
traffic in a single lane (decline). Very strict pedestrian crossing shall not be less than
regulations apply where such overtaking
may be allowed.
Figure 4.18 Required lengths of the decelerati-
on lane at the tunnel exit. Values for LS are given
412.6 Vertical curve radius in Table 4.4
The recommended vertical curve radius is
shown in Table 4.6. Direct slip road
In dips with a gentle curve the driver will
have difficulty in recognising the change
from a decline to an incline. This can LS
result in an involuntary reduction in speed
resulting in reduced traffic flow and dan- Parallel slip road

ger of collision in the rear.

The radius of the summit is designed as
for open roads in accordance with Manual L1 L2

017.
Parallel slip road
The transition from decline to incline
can be indicated with the warning sign
“Steep Incline”, or with horizontal mark-
_
> 50m L1 L2
ing on the tunnel wall.

413 Intersections Design speed

70 - 80 90 - 100
km/h
413.1 Intersections outside the tunnel
L1 70 m 90 m
entrance
L2 30 m 50 m
When the road through the tunnel has pri-

45
 ROAD TUNNELS GEOMETRIC DESIGN

Figure 4.19 Required length of acceleration lane deceleration lane commences within the
at the tunnel entrance and in the tunnel
tunnel, road signs shall be placed above
the driving line.

L1 L2 413.2 Intersections inside the tunnel

413.21 General
Intersections within the tunnel shall
always be approved by the Directorate of
L1 L2
L= entrance zone + transition zone I
(see tunnel lightning)
Public Roads.
Intersections in tunnels often require
Design speed large excavated space. Rock-mass proper-
60 70 80 90 - 100
km/h ties shall always be evaluated to ensure
L1 80 m 110 m 140 m 175 m that the required excavations are possible.
L2 30 m 50 m 50 m 50 m
With regard to lighting, no part of an
intersection shall be located closer to the
tunnel entrance than a distance correspon-
ding to the entry zone where special light-
the stopping sight distance, based on the ing requirements apply plus transition
speed limit at the tunnel exit. In tunnels in zone I (see Figure 4.19). A slip road may,
urban areas with a speed limit 50 km/h or however, commence in the transition zone
lower, this distance may be reduced where if the deceleration lane commences at least
there is satisfactory stopping sight dis- 100 m before the tunnel entrance. In the
tance to traffic islands, signs, traffic lights intersection zone and on stretches where
and other road users. Roundabouts may be much lane-changing occurs in connection
situated near to the tunnel opening if the with the intersection, the minimum lumi-
traffic speed is low and the central island nance shall be 3 cd/m2.
can be observed in good time before exit- Ventilation in the tunnel is complicated
ing from the tunnel. If the roundabout is by intersections. It is important that elec-
located closer to the tunnel than 2 x LS, tro-technical considerations are made at an
the give-way warning should be shown on early stage in the planning process.
a dual-faced sign in the tunnel. With regard to safety, the intersection in
When the junction is located outside the the tunnel shall be designed for a higher
tunnel opening, special importance must traffic volume than for corresponding
be attached to the reduction of glare prob- intersections on open roads. The ratio of
lems for traffic driving out of the tunnel. designed traffic/calculated capacity (v/k)
In two-level junctions outside the tunnel shall not exceed 0.75 for the period of
entrance, neither the entry nor exit lanes maximum traffic volume.
shall be shorter than that stated in Manual Crossroads or signal-controlled intersec-
017. The entry lanes shall have merged tions shall not be used in tunnels.
before the tunnel opening. Forks in tunnels shall be protected with
A direct slip road shall not commence buffers (see Section 405).
closer to the tunnel entrance than the stop-
ping sight distance (Figure 4.18). A paral- 413.22 Roundabouts
lel deceleration lane may commence at the Roundabouts in tunnels may be used in
tunnel entrance although can be located urban and built-up areas where the speed
entirely within the tunnel. In this event the level (defined as 85 % fractile) in the tun-
lane shall be extended for an extra 50 m nel does not exceed 60 km/h. A 3-arm
beyond the tunnel entrance. Where a mini-roundabout or a larger roundabout

46
 ROAD TUNNELS GEOMETRIC DESIGN

10m
4m

Figure 4.20 Three-armed mini-roundabout Figure 4.21 Large roundabout, three or four-
armed

with 3 or 4 arms and a raised central island er curve radius is required or where the
may be used (Figures 4.20 and 4.21). traffic volume is greater, a parallel decel-
Mini-roundabouts are primarily used on eration lane should be used.
local roads where AADT(20) is less than The entry slip roads shall end with a par-
ca. 5000. allel lane for acceleration and shall be at
3-arm mini-roundabouts entail 120- least 50 m longer than the corresponding
degree angles between the arms, and a lane on open roads as the sight conditions
marked-out central island about 1.5 m in from the slip road are more restricted in
diameter. Under these conditions the sight junctions inside the tunnel.
zone (10 x 50 m) will correspond to the Slip roads in the tunnel should be broad-
broadened approach to the junction. er on the inner curves to satisfy the
Medium sized and large roundabouts requirements for free sight in the curve. If
may be constructed with concrete or natu- possible, the slip roads should not have
ral rock pillars on the central island. sharper curves than R = 50 m.
The size of the pillars depends upon When planning two-level junctions in
rock mechanics. A free-sight zone with a tunnels, importance should be attached to
width of ca. 4 m is required around the pil- solutions which reduce the need for
lar. The width of the carriageway around changing lanes inside the tunnel.
the roundabout should be 8–10 m. For a 3- Where traffic on the entry slip road
arm roundabout with an 120 degree angle exceeds 1200 vehicles/h in designed time,
between the arms, the diameter may be consideration should be given to the entry
reduced slightly. slip road continuing as a separate lane. A
The criterion for free sight is that from a separate lane for exiting traffic should also
point 10 m behind the give-way line in be considered where there is a high risk of
each approach, there shall be 50 m free queue formation in the exit lane.
sight to the left along the circulation area Where traffic on the through-lane and
and into the previous approach road the entry/exit lanes is of such volume that
(Figures 4.20 and 4.21). there is a danger for queues, speed restric-
tions should be considered on the tunnel
413.23 Exit and Entry slip roads – two- approach rather than in the tunnel itself.
level junctions
Exit slip roads with a small amount of traf- 413.24 T-junctions
fic can be designed as a direct lane leading T-junctions should not be used in tunnels,
to a curve with R > 50 m. Where a small- although may be exceptionally permitted

47
 ROAD TUNNELS GEOMETRIC DESIGN

where the traffic volume is small with appears suddenly for road users. Sign 122
AADT(20) < 500 on the main highway, may be combined with sign 802
and AADT(20) < 100 on the side road. “Distance” positioned below sign 122, but
The design will be considered with regard shall not be used in conjunction with sub-
to the specific circumstances. signs which show the tunnel length.
The prohibition sign 314 “Height limit”
is only used for tunnels where the meas-
414 Equipment, traffic signs and road ured clearance is 4.59 m or less. Prohibition
marking sign 334 “No overtaking” and 306.8
414.1 General “Prohibited for pedestrians and cyclists” is
A detailed sign/signal plan shall be pre- only used where curves in the road or
pared for the tunnel. This is done at an other special circumstances advise this.
early stage in the project as this is essential Special regulations apply to the cross-sec-
for the design of the tunnel and can be a tion, illuminations and ventilation in tun-
decisive factor for important construction nels used by pedestrians and cyclists.
aspects. The information sign 601 “Radio sta-
Detailed regulations for traffic signs and tion” shall be used in all tunnels with
road marking are given in Manual 50 radio communication
“Traffic signs” and Manual 49 “Road The flashing red stop signal (see Section
marking” (in Norwegian). Signs and 602.207 and Manual 048 “Traffic sig-
marking outside the tunnel shall be in nals”) is indicated with sub-sign 808. No
accordance with these manuals. Some other signs shall be placed on the same
signs and selected road markings require pole as the flashing red warning sign.
to be approved. These are specified in the Barriers must bear sign 908 “Barrier”, or
manuals together with the approval be similarly designed but in red and white.
authorities. See also Section 602.208 “Remote-con-
Signs in connection with road works and trolled barriers for tunnel closure”. The
surveillance equipment are supplementary barriers should be located at least 50 m
to ordinary traffic signs and are described before the tunnel entrance to ensure suffi-
in Chapter 6 “Traffic and fire safety”. cient space in the event of evacuation,
smoke hazard, etc.
414.2 Equipment and traffic signs out- Emergency telephones and fire extin-
side the tunnel guishers, where found (See Chapter 6), are
With regard to traffic safety, signs near the installed outside the tunnel entrances. The
tunnel entrance should be reduced to a precise location will depend upon the
minimum. Signs shall be considered with actual tunnel, but it will be convenient to
respect to the individual tunnel. Some of assemble emergency equipment, emer-
the safety measures inside the tunnel will gency telephone, fire extinguishers etc at
require to be linked to signs the same place, i.e. about 50 m from the
The sign 712 “Tunnel name” with a tun- tunnel entrance.
nel symbol and length shall be used for The minimum distance between signs
tunnels exceeding 500 m in length. The given in Manual 050 “Traffic signs” also
sign is located on the right-hand side, at applies to the tunnel approach. The
least 50 m from the tunnel entrance. Manual also gives precise information on
As an alternative to sign 712, warning which signs may be attached to the same
sign 122 “Tunnel” may be used where the pole/mast and the maximum number of
tunnel entrance is not clearly visible and signs per post.

48
 ROAD TUNNELS GEOMETRIC DESIGN

200 m
712 122 314 334 306.8
802

Figure 4.22 Road signs approaching the tunnel

20-50 m
og 606

50-100 m

Rødt stoppblink
808.67
Snuplass
Eventuell bom
plasseres sammen
med stoppblink 50-100 m

601

Plassering av
ev. var. skilt
50-100 m

Figure 4. 23 Example showing location of signs in the tunnel approach

49
 ROAD TUNNELS GEOMETRIC DESIGN

601 605 606 916

Figure 4.24 Signs used in the tunnel

Consideration shall be given whether See Figure 4.24.

signs relating to the tunnel and which are The service sign 601 “Radio station” is
normally located near the tunnel entrance located outside the tunnel as described in
are better located at the last opportunity Section 414.2. Where it is possible for the
for turning or the last intersection before Norwegian Public Roads Administration
the tunnel. Examples of such signs are 314 or emergency services to be able to inter-
“Restricted height” combined with sub- rupt broadcasts with warnings to road
sign 802 “Distance”, together with a flash- users the sign must be repeated every 500
ing red stop signal with associated sub- m in the tunnel. The sign is then combined
signs and barriers. with a flashing amber warning light which
Example of the location of signs is is activated when the warning is broadcast
shown in Figure 4.23. (See Table 6.1 and Chapter 6 “Traffic and
Fire Safety”). The text on the sign shall
414.3 Traffic signs in the tunnel also refer to radio NRK channel P1 even
The number of signs inside the tunnel though the warning is broadcast on other
should be kept to a minimum. This applies channels.
particularly to large signs as the tunnel All emergency telephones are indicated
cross-section provides only restricted with service sign 605 “Emergency tele-
place for signs. Intersections in the tunnel phone”. All fire extinguishers are indicat-
or immediately after the tunnel require a ed with service sign 606 “Fire extinguish-
number of signs, and this should be taken er”. The signs shall be indicated on the
into consideration. front and reverse; alternatively signs are
All signs in the tunnel shall be clearly placed facing oncoming traffic in both
visible using either built-in or external directions.
lighting. Sign 916 “Distance marking for tunnels”
Signs in the tunnel do not differ from shows the distance to the tunnel entrance
those employed outside the tunnel. Traffic in both directions. These are relevant for
regulation signs, warning, information and tunnels longer than 3 km.
direction signs shall be considered in a Turning points are indicated with a sep-
similar manner to signs on the open road. arate sign with a flashing stop signal.
The following describes some signs which These have to be approved by the
are especially appropriate to tunnels. Directorate of Public Roads. In the event

50
 ROAD TUNNELS GEOMETRIC DESIGN

of a fire extinguisher being removed all shall be indicated according to the given
signs up to the point of closure will be cross-sections. See guidelines for use of
automatically switched on. In the direction profiled road marking. Reflectors on the
of the exit all signs are switched off. road should be considered, particularly
For emergency signs which are not traf- where lighting is poor. Normally the pro-
fic signs, see Section 602.203 “Emergency filed marking and road reflectors should
exit signs”. continue for at least 100 m outside the tun-
Certain interior-illuminated signs may nel. Otherwise the marking is as for the
be reduced in size compared to those on open road.
the open road. This applies to triangular In tunnels with poor lighting and diffi-
and circular signs where those of medium cult curves, sign 914 “Tunnel marking””
size (900 and 800 mm respectively), and may be used to improve visibility.
large size (1200 and 1000 mm respective-
ly), can be reduced by one class size. This
applies also to information signs 530–538,
which may be reduced by up to 30 percent,
and service signs 605 and 606 which can
have a width of 440 mm. For overhead
traffic lane sign 724, a minimum height
for the text of 210 mm can be used.
Manual (050) “Traffic signs” provides
details.
As far as possible effort should be made
to locate signs in the tunnel corresponding
to that on the open road. Road direction
signs require considerable space and
should be placed above the driving lanes.
The effect of signs on ventilation and illu-
mination have to be especially considered.
Normally, there is insufficient space for
more than one or two text lines on road
direction signs above the lane. The num-
ber of direction signs should therefore be
reduced to a minimum. Laterally placed
signs which are too large with regard to
the tunnel cross-section may be placed in
the emergency lay-bys. The clearance
under lateral signs should to be at least 2.0
m. See Section 403 “Tunnel cross-sec-
tions”.
See also Chapter 6 “Traffic and fire safe-
ty”.

414.4 Road marking and visibility

Warning lines, prohibitory lines and com-
binations of these together with the car-
riageway boundary line in the tunnels

51
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