A CLEAR IDEA ABOUT ROAD MARKINGS, INTERSECTIONS, ISLANDS, TRAFFIC SIGNS, SIGNALS Etc.,

1. Traffic Designs and Visual Aids
Presented By,
T. Manikandan B.Tech., M.E.,
Asst. Prof. – Dept. of Civil Engineering,
Sembodai Rukmani Varatharajan Engineering College,
Sembodai – 614809.

2. Traffic island
• A small raised area in the middle of a road which provides a safe place
for pedestrians to stand and marks a division between two opposing
streams of traffic.
(or)
• A traffic island is a solid or painted object in a road that channelizes
traffic. It can also be a narrow strip of island between roads that intersect
at an acute angle.
• If the island uses road markings only, without raised kerbs or other
physical obstructions, it is called a painted island. Traffic islands can be
used to reduce the speed of vehicles driving through.

3. Types of Traffic islands
• Divisional Islands: Divisional islands are dividing the highway in
two one way road way so that head on collision are eliminated and
accidents are reduced.
• Channelizing Islands: Channelizing islands guide the traffic into
proper channel through the intersection area.
• Pedestrian loading Islands: They are provided at regular bus
stops and similar laces for the protection of passengers.
• Rotary Islands: Rotary islands is the large central island of a rotary
intersection.

7. Rotary Islands
• Rotary intersections or round
abouts are special form of at-
grade intersections laid out for the
movement of traffic in one
direction around a central traffic
island.
• The vehicles entering the rotary
are gently forced to move in a
clockwise direction in orderly
fashion.

9. Intersection of road
• Intersection is an area shared by two or more roads.
• This area is designated for the vehicles to turn to different
directions to reach their desired destinations.
• This is because vehicles moving in different direction want to
occupy same space at the same time.
Types
There are two main types of intersection of roads:
 Grade – separated intersections or interchanges.
 At – grade intersections.

10. Grade separated intersection or interchanges
• It is a bridge that eliminates crossing conflicts at intersections by vertical
separation of roadways in space.
• Route transfer at grade separations is accommodated by interchange
facilities consisting of ramps.
• The interchange configurations are designed in such a way to
accommodate economically the traffic requirements of flow, operation on
the crossing facilities, physical requirements of the topography, adjoining
land use, type of controls, right-of-way and direction of movements.

11. Grade separated intersection or interchanges
Objective:
The ultimate objective of grade separated intersections is to eliminate
all grade crossing conflicts and to accommodate other intersecting
maneuvers by merging, diverging and weaving at low relative seed.
Classification of Grade Separated Intersection
• One of the distinctions made in type of interchange is between the
directional and the non directional.
• Directional interchanges are those having ramps that tend to follow
the natural direction of movement.
• Non directional interchanges require a change in the natural path of
traffic flow.

12. Major Interchanges
• Underpass
• Overpass
• Trumpet Interchange
• Diamond Interchange
• Cloverleaf Interchange
• Partial cloverleaf Interchange
• Directional Interchange
• Bridged Rotary

13. Underpass
• An underpass or a tunnel is an underground passageway,
completely enclosed expect for openings for ingress and egress,
commonly at each end.
• A tunnel may be for foot or vehicular road traffic, for rail traffic.

14. Overpass
• An overpass also known as a flyover, is a bridge, road, railway
or similar structure that crosses over another road or railway.
• A pedestrian overpass allows pedestrians safe crossing over
busy without impacting traffic.

15. Trumpet interchanges
• Trumpet interchanges have been used where one highway
terminates at another highway.
• These involve at least one loop ramp connecting traffic either
entering or leaving the terminating expressway with the far
lanes of the continuous highway.
• The principal advantages are low construction cost and are
useful for highways as well as toll roads.

17. Diamond interchange
• A diamond interchange is a common type of road junction,
used where a freeway crosses a minor road.
• The diamond interchange uses less space than most types of
freeway interchange, and avoids the interweaving traffic flows
that occur in interchanges such as the cloverleaf.
• Diamond interchanges are most effective in areas where traffic
is light.

19. Cloverleaf interchange
• A cloverleaf interchange is a two-level interchange in which left
turns are handled by ramp roads.
• To go left (in right-hand traffic), vehicles first continue as one road
passes over or under the other, then exit right onto a one-way
three-fourths loop ramp (270) and merge onto the intersecting
road.

20. Partial cloverleaf interchange
• Partial clover leaf is a modification that combines some
elements of a diamond interchange with one or more lops of a
cloverleaf to eliminate only the more critical turning conflicts.
• It provides more acceleration and deceleration space on the
freeway.

21. Directional interchange
• A Directional interchange provides direct for left turns.
• These interchanges contain ramps for one or more direct or semi
direct left turning movements.
• Interchanges of two freeways or interchanges with one or more
very heavy turning movements usually warrant direct ramps,
which have higher speeds of operation and higher capacities,
compared to loop ramps.

23. At grade intersections
• At-grade intersections in which all the exchanges between the
roads take place on the sane plane.
These are of two types
• Standard at-grade intersections
• Round about at-grade intersections.

25. Simple intersections
• Simple intersections maintain the street’s typical cross-section
and number of lanes throughout the intersection, on both the
major and minor streets.
• Simple intersections are best-suited to locations where auxiliary
(turning) lanes are not needed to achieve the desired level-of-
service.

26. Channelized intersections
• Vehicles approaching an intersection are directed to definite
paths by islands, marking etc. and this method of control is
called channelization.
• Channelized intersection provides more safety and efficiency.
• It reduces the number of possible conflicts by reducing the area
of conflicts available in the carriageway.
• If no channelizing is provided the driver will have less
tendency to reduce the speed while entering the intersection
from the carriageway.

28. Traffic Regulation
Various Traffic regulatory measures are:
 Issue driving license- by checking age and conducting test drive
 Registration of Vehicles
 Transfer of Ownership
 Distinction between private and public vehicles
 Transport authorities
 Speed limit and Limits of Weight
 Parking and halting Places
 Insurance fees
 Punishment of Violation and offences
 Provision of Control Devices

29. Traffic Control Devices
The various aids and devices used to
control, regulate and guide traffic is
called TCD
Signs
Regulatory
Warning
Informatory
Signals
Fixed Time
Manually Operated
Traffic actuated
Pedestrian
Special Traffic
Marking
Pavement
Kerb
Object
Reflector unit
Delineators
Islands
Divisional
Channelizing
Pedestrian loading
Rotary
Lights

30. Traffic Signs
(A) Regulatory Signs:
Regulatory Signs are meant to inform the road user of certain laws,
regulations and prohibitions. The violation of these signs is a legal offence.
Eg.
 Stop and give way sign
 Prohibitory signs
 No Parking signs
 Speed limit and vehicle control signs
 Restriction end sign
 Compulsory direction control and other signs

31. Regulatory Signs

32. Warning Signs

33. Informatory Signs

34. Variable message signs can be placed in a wide range of places like
highways, major road junctions, and urban arteries.
Typically installed at the side or above the roadway, the VMS uses
text and graphics in monochrome or color.
Variable Message Signs (VMS)

35. Traffic Signals
Definition:
Traffic Signals are control devices which could alternately direct the traffic to
stop and proceed at intersections using red and green traffic light signals
automatically.
Advantages of Signals:
 Signal is provided at intersection to manage the traffic flow.
 Signals provide safety to vehicular traffic and pedestrian. They reduce and
avoid the accidents.
 Signals are easy to understand compare to traffic police management at
intersection.

36. Disadvantages of Signals:
 Fast moving vehicles may cause rear end collision at signalized
intersection
 Improper design of signal cycle length can cause fixed delay.
 Duration off-peak hour unnecessary delay occur at signalized
intersection.

37. Road Marking
 Road marking are made of lines, patterns, words, symbols or
reflectors on the pavement, kerb, sides of islands or on fixed object
within or near the roadway to control, warn, guide, or regulate the
traffic.
 The marking are made by using white, black, yellow, colour paints.
 Longitudinal lines are 10 cm thick and traverse lines should be
made in such a way that they are visible at sufficient distance in
advance. Yellow color marking are used to indicate parking
restrictions, continuous center line and barrier line markings.
 Longitudinal solid lines are used as guiding and regulating lines
and are not meant to be crossed by the driver.

39. Centre Line
On undivided two-way roads, the centre line separates the
opposing streams of traffic and facilitates their movements.
Lane lines
The Divided Lines visible in the pictures above are called Lane
Lines.

40. Road Delineators
Are devices or treatment to outline the roadway or portion there of to
provide visual assistance to drivers about the alignment of a road
ahead, especially at night.
Types of delineators are:
 Roadway indicators
 Hazard markers
 Object markers