Chapter 5
Fundamentals of Traffic Flow and Queuing Theory
5.1
INTRODUCTION
•
Highways seek high mobility (speed) while considering safety.
•
Understanding traffic flow and queuing is the key to evaluating highway performance
(mobility provided)
5.2
TRAFFIC STREAM PARAMETERS
Consider uninterupted flow:
•
No stop signs
•
No traffic signals
5.2.1
Traffic Flow, Speed, and Density
•
Traffic flow:
q =
n
t
(5.1)
Where:
q
=
traffic flow in vehicles per unit time,
n
=
number of vehicles passing some designated roadway point during time
t
,
t
=
duration of time interval.
•
In addition to the total number of vehicles passing a point in some time interval,
consider the time between the passing of successive vehicles
•
Headway
- time between the passage of the front bumpers of successive vehicles, at
some designated highway point
Time headways are related to
t
, as defined in Eq. 5.1, by
t =
h
i
i =
n
1
∑
(5.2)
Where:
t
=
duration of time interval,
h
i
= time headway of the
i
th vehicle (the time that has transpired between the arrival
of vehicle
i
and
i
-1),
n
= number of measured vehicle time headways at some designated roadway point.
Substituting Eq. 5.2 into Eq. 5.1 gives
∑
n
i =
i
h
n
q =
1
(5.3)
or

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