CIVIL ENGINEERING

1. CAPACITY ESTIMATION OF
UNSIGNALIZED INTERSECTION
ON INTER CITY ROADS IN
TAMIL NADU
By
M.HEMAVATHY
2013266032
Guided by
Dr. K.GUNASEKARAN

2. UNSIGNALIZED
INTERSECTION

3. INTRODUCTION
Most commonly noticed type of
road junctions in highway
network.
Intersections with no stop signs,
or intersections where the driver
must judge whether stopping is
appropriate.
No explicit traffic control
measures are adopted.

4. NEED FOR THE STUDY
Highest accident rate
40- 70 % among all kinds of
road facilities
NEEDS “DECISION
SUPPORTIVE”
MEASURES
TREATMENT IS
COSTLY
Conventional method of
treatment for unsignalized
intersection is costly.
ROUNDABOUT-25 LAKHS
when to go for treatment?
what is the type of control
required at unsignalized
intersection
what is the safe gap for two
wheeler, car, auto, bus , truck.

5. OBJECTIVES OF THE STUDY
To study the heterogeneous traffic flow characteristics at
unsignalized intersection using videographic methods.
To estimate and compare the critical gap values for different
types of vehicles using various methods.
To determine the capacity of the selected unsignalized
intersection in Tamil Nadu

6. STUDY METHODOLOGY

8. STUDY AREA
 In present study, unsignalized three armed intersection
was selected which offers enough number of gaps to
the vehicles on minor road to extract good number of
observations in terms of accepted and rejected gap.
 Data have been collected during morning peak for 4
hours and data would be collected using two cameras
mounted at the height of 8-10 meters with the help of
Pneumatic mast.

9. Sr.
No
Name of the
intersection
Height of
Camera
Positioning
and
Location of
Camera
Date of
Survey
Duration
of Survey
(along
with Time
and
Hours)
Data
Retrieval
Status from
Video
1 Bukkathurai
Intersection 10meter
1st jan
2015
8 am to 1
pm completed
2 Kancheepuram-
NH 4
10 meter 2nd jan
2015
8 am to 4
pm
completed
3 Chegalpet
Intersection
10 meter
YET TO BE MEASURED

10. Kancheepuram-NH-4 Intersection
Bukkathurai
Intersection
Chengalpet Intersection

11. Geometrical Data Identification
 Traffic flow at selected intersections was carefully studied
and it was invariably observed that all the vehicles which
have to stop before entering into the intersection stops at
nearly 2 meter inside the intersection.
 Based on these site observations, entry and exit lines have
been marked on-site using reflective tapes.
 It was observed that the speed of the vehicles measured
near the stop line is found to be influenced for the
accepted gaps.
 Hence it is decided to compare the influence of speeds
measured at stop line and a distance (at least greater than
Safe Stopping Distance) away from the stop line using
SEPARTE CAMERA .

12. Bukkathurai Intersection

13. Kancheepuram-NH-4 Intersection

14. Data Extraction Methodology
For present study of acceptance and rejection
behaviour, following two movements have
been considered in this analysis
Right turn from major street to minor road
Right turn from minor stream to major road

15. DATA EXTRACTION

16. SAMPLE DATASHEET

17. Data Analysis
1. Use of statistical method to calculate critical gap of each
defined vehicle category. The method of analysis is to be
carefully selected as it will have effect on results. Literature
says Maximum Likelihood Method (MLM) is the most
accurate method, but it requires an iterative process. Also,
this method considers accepted and rejected gaps in pairs.
2. Determine follow up time headway from recorded field data
for each vehicle category.
3. Develop a relation between critical gap and follow up time
for different types of vehicles.
4. Draw the capacity curves for different types of vehicles and
amount of conflicting traffic.

18. PROPORTION OF GAPS

19. METHODS OF CRITICAL GAP
ESTIMATION

20. GREEN SHIELD METHOD

21. RAFF’S METHOD

22. Method Conditions Used When Drawbacks Data
Requirement
Green shield Saturated Closest number of
acceptions &
rejections used as
critical gap
Gap accepted only
by 50% drivers
Accepted and
rejected gap are to
be considered
Raff Under saturated Non homogenous
& inconsistent gap
acceptance
behavior
Number of
accepted gaps
shorter than it is
equal to number or
rejected gaps
longer than it
Differentiated as
length of gap
greater or smaller
into acception &
rejection
Harder Under saturated Only applicable
for acceptable
gaps
Gaps alone for
estimating critical
gap
Only accepted gap
sizes differentiated
with their
lengths(range)
MLM saturated Ignores below
1sec and above
21sec gaps
Accepted and
rejected gaps in
pairs is required

23. .
CAPACITY ESTIMATION
The potential capacity of can be computed using the
formula
Where, cpx is the potential capacity of minor
movement (veh/h),
vcx is the conflicting flow rate for movement (veh/h),
tcx is the critical gap for minor movement ,
tfx is the follow-up time movement .

24. REFERENCES
1. Sahar Nabaee (2011), “An Evaluation Of Gap Acceptance Behavior At Unsignalized
Intersections”, Proceedings of the 6th International Driving Symposium on Human Factors in
Driver Assessment, Training and Vehicle Design, California Oregon State University.
2. Joewono Prasetijo (2005), “ Development of new method of capacity analysis at
unsignalized intersections under mixed traffic flow” Proceedings of the Eastern Asia Society for
Transportation Studies, Volume 5.
3. Joewono Prasetijo (2011), “Capacity of unsignalized intersection under mixed traffic
condition” Sixth International Symposium on Highway Capacity and Quality of Service.
4. Roess, Roger P., Elena S. Prassas, & William R. McShane. (2011). Traffic Engineering
(Fourth ed.). Upper Saddle River: Pearson Higher Education Inc.

25. REFERENCES
4. Joewono Prasetijo (2011), “Capacity of unsignalized intersection under mixed
traffic condition” Sixth International Symposium on Highway Capacity and
Quality of Service
5. Sahar Nabaee (2011), “An Evaluation Of Gap Acceptance Behavior At Unsignalized
Intersections”, Proceedings of the 6th International Driving Symposium on Human Factors
in Driver Assessment, Training and Vehicle Design, California Oregon State University.
6. Roess, Roger P., Elena S. Prassas, & William R. McShane. (2011). Traffic
Engineering (Fourth ed.). Upper Saddle River: Pearson Higher Education Inc.

26. THANK YOU