Medians/Traffic separators , kerbs, Road margins , Shoulders , Guard rails, embankment slopes

1. DEPARTMENT OF
CIVIL ENGINEERING
Medians/Traffic separators
Kerbs
Road Margins
Er. Ramprasad Kumawat
M.Tech

2. CONTENT
• Medians/Traffic separators
• Kerbs
• Road Margins

3. Medians/Traffic separators
• In highways with divided carriageway, a
median is provided between two sets of traffic
lanes intended to divide the traffic moving in
opposite directions.
• The main function of the median is to prevent
head-on collision between vehicles moving in
opposite directions on adjacent lanes.
• The median is also called or traffic separator.

4. • The traffic separators used may be in the form
of pavement markings, physical dividers or
area separators.
• Pavement marking is the simplest of all these,
but this will not rule out head-on collision.
• The mechanical separator may be suitably
designed keeping in view safety
considerations.

5. • The medians/traffic separators may also serve
the following functions:
• (a) to channelize traffic into streams at
intersections
• (b) to shadow the crossing and turning
traffic
• (c) to segregate slow traffic
• (d) to protect pedestrians

6. • It is desirable to provide wide median/traffic
separators of 8 to 14 m width so that it is
possible carry out future widening of the
carriageway towards the median.
• But the width should be decided in conformity
with the availability of land and its cost.
• A minimum of 6 m is required to reduce head
light glare due to vehicles moving in opposite
directions on either side of the median at night.
• The glare can be reduced in narrower strips by
planting shrubs.

8. • The IRC recommends a minimum desirable
width of 5.0 m for medians of rural highways,
which may be reduced to 3.0 m where land is
restricted.
• On long bridges the width of the median may
be reduced up to 1.2 to 1.5 m.
• The medians should normally be of uniform
width on a particular road, but where change in
width is unavoidable, a transition of 1 in 15 to
1 in 20 must be provided.

9. • Thus in highways with divided carriageway,
the total road width depends on the width of
pavement or carriageway and the width of the
median/dividing island/traffic separator.
• On urban highways with six lanes or more,
medians should invariably be provided.

10. • The minimum recommended width of medians
at intersections of urban roads are 1.2m for
pedestrian refuge, 4.0 to 7.5 m for protection
of vehicles making right turn and 9.0 to 12 m
for protection vehicles crossing at grade.
• The absolute minimum width of median in
urban area is 1.2 m and desirable minimum is
5.0 m.

11. Kerbs
• Kerb indicates the boundary between the
pavement and median or foot path or island or
shoulder.
• It is desirable to provide kerbs on urban roads.
Refer Fig. 4.3. There are a variety of kerb
designs.
•

13. • Kerbs may be mainly divided into three
groups based on their functions.
• (a) Low kerb' or 'mountable type kerb‘
encourages traffic to remain in the through
traffic lanes, yet allows the driver to enter the
shoulder area at slow speed.
• The height of this type of kerb is about 100
mm above the pavement edge with a slope or
batter to enable vehicles to climb the kerb at
slow speed.
• This type of kerb is provided at medians and
channelization schemes and is also useful for
longitudinal drainage system

14. • (b) `Semi-barrier type kerb' is provided on
the periphery of a roadway where the
pedestrian traffic is high.
• This type of kerb has a height of about 150
mm above the pavement edge with a batter of
1:1 on the top 75 mm.
• This kerb prevents encroachment by the
parking vehicles, but at acute emergency it is
possible to drive over this kerb with some
difficulty

15. • (c) Barrier type kerb is provided in built-up
areas adjacent to foot paths with
considerable pedestrian traffic.
• The height of kerb stone is about 200 mm
above the pavement edge with a steep batter of
1.0 vertical 0.25 horizontal

16. • At times submerged kerb is provided on rural
roads between pavement edge and shoulders.
• The submerged kerb provides lateral
confinement and stability to the flexible
pavements in general and to the granular base
course of pavements in particular.

17. Road Margins
• The various elements included in the road
margins are shoulder, guard rail, footpath,
drive way, cycle track, parking lane, bus bay,
lay-bye, frontage road and embankment slope.

18. • Shoulders
• The important functions of shoulders are:
• (a) The capacity of the carriageway and the
operating speeds of vehicles increase if the
shoulders are laid and maintained in good
condition

19. • (b) Shoulders serve as emergency lanes for
vehicle compelled to be taken out of the main
carriageway or roadway.
• Shoulders should have sufficient load bearing
capacity to support loaded truck even in wet
weather

20. • (c) Shoulders also act as service lanes for
vehicles that are disabled. The width of
shoulder should be adequate to accommodate
stationary vehicle fairly away from the edge of
adjacent lane.

21. • Guard rails
• Guard rails are provided at the edge of the
shoulder when the road is constructed on a fill so
that vehicles are prevented from running off the
embankment, especially when the height of the
fill exceeds 3 m.
• Various designs of guard rails are in use.
• Guard stones (painted with black and white strips)
are installed at suitable intervals along the outer
edge of the formation at horizontal curves of
roads running on embankments along rural areas
so as to provide better night visibility of the
curves under head lights of vehicles.

22. • Footpath or side-walk : Min width : 1.5 m to
2.0m.
• Drive ways : connect the highway with
commercial establishment like fuel-stations
service-stations.
• Cycle tracks : min. width 2m provided.
• Parking lane : min. lane width 3.0m.

23. • Embankment slopes
• Embankment slopes should be as flat as possible
for the purpose of safe traffic movement and also
for aesthetic reasons.
• Though from the slope stability point, a steeper
slope may be possible, the slope may be kept as
flat as permitted by financial considerations.
• Road side landscaping can improve the aesthetic
features of road side, making road travel more
pleasant.
• For safety considerations, the desirable slope for
the embankment is 1 in 3

24. Fig : Cross section details

25. • THANKS!
• Gmail: ramkumawat001@gmail.com