1. Intersection safety
Semarang
23rd & 24th April 2012
Phillip Jordan, Consultant
Road Safety International Pty Ltd

2. Objectives of this presentation
• To explain why we need to consider the safety of intersections.
• To give some details of how to improve safety at intersections.

3. An intersection can be defined as :
“a place where two or more roads meet at grade”.
Intersections are particularly high risk locations because different road users
(trucks, buses, cars, pedestrians, and motorcycles) are required to use the
same space.

4. Intersections are critical locations in the road network in
terms of capacity, level of service and safety.
They are the place where opposing streams of traffic have to
compete for space and time.
They are high risk locations for crashes because road users on
conflicting paths in intersections are required to use the same
space, and a collision is only avoided if they are separated in
time!
The art of the crash investigator

5. SERIOUS CASUALTY CRASHES – AUSTRALIA 2010

6. Intersections also present a risk of serious injury or
death when a crash occurs because of the potential for
high relative impact speeds.
Intersections are the location of up to 50% of reported
urban crashes in most countries.
They are the location of between 10-20% of reported
rural crashes in most countries.
The art of the crash investigator

7. Intersections can be found in urban and rural
areas. They are usually in one of four main
groups:
– Four way (cross road) intersections
– T intersections
– Y intersections
– Multi-leg intersections
The art of the crash investigator

9. The main forms of control at intersections are:
– Road Rules (no physical control) - relying on a priority rule to
indicate right of way;
– Priority road designated by ‘Give Way’ or ‘Stop’ signs;
– Roundabout;
– Traffic signals, with partial control of right turning traffic;
– Traffic signals, with full right turn control;
The art of the crash investigator

10. The basic principles you need to consider and try to
provide for safe intersections are:
• Reduction in the relative speed between vehicles
• Give precedence to major traffic movements;
• Separate conflicts in space and time;
• Define and minimize conflict areas;
• Define the vehicle paths;
• Provide clear indications of right-of-way requirements;
• Provide for all vehicular and non-vehicular traffic likely to
use the intersection;
• Simplify the driving task;
• Minimize road user delay.
The art of the crash investigator

11. Conflict points at intersections
The fewer
conflict
points – the
safer!
24 points of major conflict

12. Conflict points at intersections
The fewer
conflict
points – the
safer!
6 points of major conflict

13. Conflict points at intersections
The fewer
conflict
points – the
safer!
4 points of major conflict

14. ASD is the minimum level of sight distance which
should be provided at an intersection. It is equal
to car stopping sight distance (SSD) – which is
defined as the distance travelled by a vehicle
between the time when the driver receives a
stimulus indicating a need to stop, and the time
that the vehicle does come to a stop.
This distance is sufficient to allow drivers/riders to
be able to see the line marking and kerbing at the
intersection.
The art of the crash investigator

15. Basic elements of intersection safety

17. • ASD – approach sight distance • ASD addresses overshoot crashes
• SISD – safe intersection sight • SISD addresses restart problems
distance

20. With intersection right angle crashes – we need
to determine if the crash is an overshoot or a
re-start
Why?
Because our countermeasure(s) may be quite
different

21. With intersection right angle crashes – we need
to determine if the crash is an overshoot or a
re-start
Overshoot – the driver did not know the intersection
was there
Re-start – knew it was there, slowed, maybe
stopped, but selected a “wrong” gap

22. Overshoot – the driver did not know the
intersection was there
--------------------------------------------------------
Improve Approach Sight Distance
Make intersection more conspicuous
Advance warning signs
Advanced direction signs
Duplicate GW or Stops
Lighting
Roundabout or signals

23. Re-start – knew intersection was there,
slowed, maybe stopped, but selected a
“wrong” gap
------------------------------------------------------------
Improve Safe Intersection Sight Distance
Maximise sight lines
Reduce speeds,
Alter the traffic control
Geometric changes
Cut trees/grass
Reduce speed limits
Roundabouts or signals

25. Y junctions are
very dangerous

26. We need to eliminate
Y junctions

31. We need to eliminate
Y junctions

32. Treatment of low angle intersections
Modified Treatment
•Controls turn speed
•Reinforces priority
for increased safety
• Enhances sight lines

33. Treatment of low angle intersections

34. This is not the way to safely
manage traffic for the future.
Keep intersections open and
provide correct traffic control

35. Roundabouts are the safest form of
intersection control. Why?
The art of the crash investigator

36. Why are roundabouts “safe”?
• Few conflict points (only four)
• Good geometry induces slow entry speeds
• Clearly defined “right of way”
• Simple decision making process for drivers/riders
• Low relative impact speed if collisions occur
The art of the crash investigator

38. The art of the crash investigator

42. Always look for visual
deceit at any site

51. Traffic signals

52. Traffic signals

54. Vehicle actuated traffic signals are best.
-They reduce lost time.
-They usually have “in ground” detector loops
that record the presence of a vehicle and tell
the controller to give that approach a green
signal.
- Much more efficient than fixed time signals –
and also much safer

59. Summary
 Road safety engineering is a profession that can greatly
reduce road crashes at intersections

60. I look forward to your questions….