This document discusses key concepts in traffic engineering. It begins by defining traffic engineering as the branch of civil engineering dealing with the safe and efficient movement of people and goods using roads. It then outlines some basic components of traffic engineering like road users, vehicles, roads/highways, and control devices. The majority of the document defines and explains important traffic flow parameters like speed, volume, density, spacing, headway, clearance, gap, and lane occupancy. It provides equations relating parameters and discusses units of measurement. The document aims to introduce foundational traffic engineering concepts.

1. 1
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
Introduction to Traffic
Engineering
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
Traffic Engineering
Definition: Branch of civil engineering that uses
engineering techniques to achieve safe, efficient,
and economic movement of people and goods.
Traffic Engineers: manage, organize, and control
the actual movement of vehicles and pedestrians
on the facility.
Basic Components in Traffic Engineering:
• Road users (driver, pedestrian, cyclists)
• Vehicles
• Roads and highways
• Control Devices

2. 2
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
Traffic Flow
Characteristics
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
The theory of traffic flow can be defined as:
A mathematical study of the movement of vehicles
over road network.
Definition of Traffic Flow

3. 3
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
1. SPEED (V)
2. VOLUME (q) = FLOW
3. DENSITY (K)
1. HEADWAY (h)
2. SPACING (S)
3. OCCUPANCY ( R )
4. CLEARANCE (C )
5. GAP (g)
Traffic Flow Parameters
Primary Parameters
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
6
Traffic Flow Parameters
1. Speed
• In a moving traffic flow, each vehicle travels at
a different speed.
• Thus, the traffic stream does not have a single
characteristic speed but rather a distribution of
individual vehicle speeds.
• From the distribution of vehicle speeds, a
number of “average” or “typical” values may
be used to characterize the traffic stream as a
whole.

4. 4
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
7
Traffic Flow Parameters
 Speed (contd..)
• Average or mean speeds can be computed in two
different ways:
1. Space Mean Speed (SMS) is defined as the average speed
of all vehicles occupying a given section of a highway over
some specified time period.
2. Time Mean Speed (TMS) is defined as the average speed of
all vehicles passing a point on a highway over some
specified time period.
• Time mean speed is a point measure, while space mean
speed is a measure relating to a length of highway or
lane.




it
nd
n
it
dSMS
n
it
d
TMS


‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
8
Traffic Flow Parameters
 Speed (contd..)
• where, d is the distance traversed, n is the
number of travel times observed and ti is
the travel time for i-th vehicle.






it
nd
n
it
dSMSand
n
it
d
TMS

5. 5
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬ 9
Traffic Stream Parameters
 Speed (contd..)
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬ 10
Traffic Stream Parameters
 Speed (contd..)




it
nd
n
it
dSMS
n
it
d
TMS



6. 6
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
SPEED ( V )
Rate of motion ( Distance / Unit time)
There are 3 more types of speeds:
3- Spot Speed
‫اللحظية‬ ‫السرعة‬‫والتى‬‫السيارة‬ ‫عداد‬ ‫على‬ ‫مالحظتها‬ ‫يمكن‬
4- Running Speed
‫فقط‬ ‫الحركة‬ ‫زمن‬ ‫أساس‬ ‫على‬ ‫مقاسة‬ ‫السرعة‬
5- Overall Speed
‫التأخيرات‬ ‫متضمنا‬ ‫للرحلة‬ ‫الكلى‬ ‫الزمن‬ ‫أساس‬ ‫على‬ ‫مقاسة‬ ‫السرعة‬
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
12
Traffic Flow Parameters
Volume and Flow
• Volume is defined as the number of vehicles that pass
a point on a highway, or a given lane or direction of a
highway, during a specified time interval.
• Usually expressed as vehicles per unit time, for
example, vehicles per hour or vph.
• Rate of Flow is the equivalent hourly rate at which
vehicles pass a point on a highway lane during a time
period less than 1 hour.

7. 7
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
13
Traffic Flow Parameters
• Volume and Rate of Flow are two different measures.
• Volume is the actual number of vehicles observed or
predicted to be passing a point during a given time
interval.
• Rate of flow represents the number of vehicles
passing a point during a time interval less than 1
hour, but expressed as an equivalent hourly rate.
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
14
Traffic Flow Parameters
• A volume of 200 vehicles observed in a 10-minute
period implies a rate of flow of:
(200 x 60)/10 = 1200 veh/hr
• Note that 1200 vehicles do not pass the point of
observation during the study hour, but they do pass
the point at that rate for 10 minutes.

8. 8
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
Density or Concentration
• It is defined as the number of vehicles occupying
a given length of a roadway, averaged over time,
usually expressed as vehicles per mile (veh./mi)
or vehicles per mile per lane (v/mi/ln).
q = v * k
where:
q = rate of flow (veh/hr)
v = average travel speed (mph)
k = average density (veh/mi)
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
Density
No of vehicles/Distance
Density

9. 9
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
Spacing (s)
• Front bumper to front bumper distance
between successive vehicles
S1-2S2-3
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
Spacing
Spacing

10. 10
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
T=0 sec
Headway (h)
• Time between successive vehicles
passing a fixed point
T=3 sec
h1-2=3sec
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
Clearance and Gap
Clearance: is defined as the distance
between successive vehicles in a traffic
stream as measured from front bumper of the
behind vehicle to back bumper of the front
vehicle
Gap: is the corresponding time between
end of the front vehicle and front of the behind
vehicle

11. 11
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
Clearance (c) and Gap (g)
• Front bumper to back bumper distance
and time
Spacing (ft) or headway (sec)
Clearance (ft) or Gap (sec)
 Clearance (ft) =
(spacing) – (average
vehicle length)
 Gap (sec) =
(headway) – (time
equivalence of the
average vehicle
length)
Gap: is the corresponding time between end of
the front vehicle and front of the behind
vehicle
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
Clearance
Clearance

12. 12
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
Lane Occupancy
• Ratio of roadway occupied by vehicles
L1L2L3
D
D
L
LO i
i

‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
• Speed (v) – ft/sec or mph
• Flow (q) – veh/sec or vph
• Density (k) – veh/ft or vpm
• Spacing (s) – ft/veh
• Headway (h) – sec/veh
• Clearance (c) – ft/veh
• Gap (g) – sec/veh
Remember, units are critical!
Units

13. 13
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
Fundamental Relationships
• q = k  v
(veh/hr) = (veh/mi)  (mi/hr)
• h = 1 / q
(sec/veh) = 1 / (veh/hr)  (3600)
• s = 1 / k
(ft/veh) = 1 / (veh/mi)  (5280)
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
Types of Facilities
• Uninterrupted flow
• Freeways
• Multilane highways
• Two-lane highways

14. 14
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
Types of Facilities
• Interrupted flow
• Signalized streets
• Un-signalized
streets with stop
signs
• Transit lanes
• Pedestrian
walkways
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
35
Speed, Flow and Density Relationship
• Assume
• We have
BkAv 
2
BkAkkvq 
 
B
v
v
B
A
B
vAv
q
2




Jam
Density
A/2
q=kv
Jam
Density

15. 15
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
37
General properties for any
traffic flow model
• Need to satisfy four boundary conditions
• Flow is zero at zero density
• Flow is zero at maximum density
• Mean Free-Flow Speed occurs at zero density
• Flow-density curves are convex
(i.e. there is a point of max flow)
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬ 38
Connections between speed,
density and flow
• A: almost zero density, free-flow speed, very low
volume
• B: increased density, reduced speed, increased
volume
• C: increased density, reduced speed, max volume
• D: jam density, min speed (crawling), very low
volume

16. 16
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
39
Traffic Stream Parameters
 Since a given flow may occur under two completely
different operating conditions (stable and unstable),
volume or rate of flow cannot be used as a measure
describing the operational quality of the traffic
stream.
 Speed and density, however, are good measures of
the quality of operations, as both uniquely describe
the state of the traffic stream.
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
Greenshield’s Model
• Assume a linear relationship between v and k:
High Density = Low
Speed
Low Density =
High Speed
vf
kj
k
k
v
vv
j
f
f 









17. 17
‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
Greenshield’s Model
K
Q
Max flow
qmax
K0 Kj
vf v0
2
k
k
v
kvq
j
f
f 








k
k
v
vv
j
f
f 








‫والتكنولوجيا‬ ‫للهندسة‬ ‫العالي‬ ‫مصر‬ ‫معهد‬–‫المدنية‬ ‫الهندسة‬ ‫قسم‬-‫المنصورة‬
Greenshield’s Model
Q
V
Max flow
Qma
x
Vf
V0
1/k0
Density=
inverse of slope