Lecture #7
Chapter 16: Principles of
Intersection Signalization (cont.)
Objectives

Understand concept of delay and how it
relates to the traffic stream
Intersection Delay

What are the different measures of delay?
Roess, P. R., W. R. McShane, E. S. Prassas.
Traffic Engineering. Prentice Hall
Intersection Delay
What are the different components of delay?
2
– Uniform Delay (UD)
C [1  ( g / C )]
UD 
2 [1  (v / s)]
25
20
Cum. Arrivals
15
Cum.
Departures
10
5
Time (sec)
21
17
13
9
5
0
1
Cumulative Vehicles (veh)

Intersection Delay

What are the different components of delay?
40
Cum. Arrivals
30
Cum.
Departures
20
10
Time (sec)
168
140
112
84
56
28
0
2
(v / c )
RD 
2v[1  (v / c)]
50
0
Cumulative Vehicles (veh)
– Random Delay (OD)
Intersection Delay

How is signalized intersection delay
modeled?
– d = 0.90 [UD + RD]
Signal Cycle

What cycle minimizes signalized
intersection delay?
1 / 5L  5
Co 
1   (v / s ) c
Co
=
minimum delay cycle (sec)
L
=
total lost time (sec)
(v/s)c =
saturation flow ratio for critical movement
Signal Cycle

How sensitive is delay to cycle time?
– ¾C–1½C
– Why is this significant to a traffic engineer?
Intersection Overflow Delay
What would long term overflow look like?
T1  T2
OD 
[(v / c)  1]
2
100
80
Cum. Arrivals
60
Cum.
Departures
40
20
Time (sec)
168
140
112
84
56
28
0
0
Cumulative Vehicles (veh)

Intersection Overflow Delay

Are there any
practical
problems
associated with
the delay
model?
Intersection Delay: Bridging
the Gap

There are a variety of delay models
– Australian
– TRANSYT
– HCM (isolated intersection)
 Based on theoretical UD and OD
 Calibrated using X2

[1  ( g / C )] 2
16 X 
2
2
d  0.38C
 173 X ( X  1)  ( X  1) 

[1  ( g / C ) min[ X ,1.0]]
c


Intersection Delay: Urban
Signalized Intersections

Does arrival at an intersection affect delay?
– {link to Excel file}
Intersection Delay: An
Approximation

“No claim is made that the formulas are
correct, but rather that they yield answers
which do not violate elementary logic in the
region of v/c near unity where neither the
steady-state nor the oversaturation models
can be expected to yield reasonable results.”
Intersection Delay Simulation

How have these delay models been
validated?
Intersection Stopped Delay
Conversion

What about the constant, 1.3, used to
convert approach delay to stopped delay?
Intersection Delay Sample
Calculations
 Given:
– v = 1100 vph
– s = 2000 vphg
– C = 120 sec
– g/C = 0.52

Find:
– Average stopped delay for the first 15 minutes of the
specified conditions
Conclusion

New Homework Assignment:
– Check web for HWK #3

Homework Assignment due:
– Assignment #2

Lab Announcements
– Data collection Monday, next week