Conen 442 module1a: Elements of Traffic System

ConEn 442:
Transportation Engineering
Wael M. ElDessouki, Ph.D.
ElDessouki
CONEN 442 Transportation Engineering S2021
1

CONEN 442
Transportation
Engineering
2
 Module 1: Traffic Engineering: (5 weeks)
 Basic Characteristics,
 Speed Study, Volume Study
 Capacity and LOS Analysis
  Quiz 1: Feb 10th, 2021 11:00-12:00 pm
 Traffic Control Devices and MUTCD
 Module 2: Highway Design: (4 weeks)
 Highway Classification
 Design Criteria,
 Midterms Exam I : Feb 28th ,2021- 10:00-12:00 pm
 Horizontal & Vertical Alignment
 Module 3: Pavement Design & Construction (4 weeks)
 Flexible Pavement
  Quiz 2: Mar 24th, 2021 11:00-12:00 pm
 Design &Construction
 Rigid Pavement
 Field Compaction Tests
 Quantity Surveying & QC Issues
 Midterm Exam II: Apr 4th ,2021, 10:00-12:00 pm
ElDessouki CONEN 442 Transportation Engineering S2021

Grading,
Exams..etc*
3
Course Assessment:
 2 Mid-term Exams 40%
 Extras: Quizzes 2*5% + HW, participation,,, etc. 20%
 Final Exam 40%
Textbooks & References:
 Roess, R. P., Prassas, E. S., and McShane, W. R., “Traffic
Engineering”, Fourth Edition, Prentice-Hall, 2011.
 Garber Hole “Traffic and Highway Engineering” 2nd Edition
 HCM 2000 (SI Units)
 Selected AASHTO design Tables and Handouts
CONEN 442 Transportation Engineering S2021 ElDessouki

Module 1:
Traffic Engineering
Wael M. ElDessouki, Ph.D.
4

Introduction
Q: What is Traffic Engineering?
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A: Definition from the Institute of Traffic
Engineers(ITE):
“The phase of transportation engineering that
deals with the planning, geometric design and
traffic operations of roads, streets, and highways,
their networks, terminals, abutting lands and
relationship with other modes of transportation”

Introduction
Objectives of Traffic Engineering:
Primary Objective:
 SAFETY
Secondary Objectives:
 Speed
 Comfort
 Convenience
 Economy
 Environmental compatibility
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Elements of Traffic System
 Road Users
Drivers, Passengers, Pedestrians, and Bicyclists
 Vehicles:
Private Autos, Trucks, and Busses
 Infrastructure:
Highways, Streets, Intersections, Roundabouts, Bridges, Tunnels,
Railways…..etc
 Traffic Control Devices:
Signs & Traffic Signals
 Environment:
Weather , Lighting Conditions, …etc
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Characteristics
of Traffic System
Elements:
Road Users:
• Drivers
• Pedestrians
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Road User Characteristics:
Drivers & Pedestrians Limits
 Road users are diverse population and have different
characteristics.
 However, their characteristics follow a normal distribution, and,
in our analysis, we will focus on 85% & 15%
 85th % represents the maximum
 15th % represents the minimum
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Drivers’ Field of Vision
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1- Road Users Visual Characteristics
Vision is the most important sensory system
for the task of driving a vehicle.
Q: Why?
A: Because drivers rely on their vision to:
1- Detect hazards
2- Make turn decisions
3- Selecting Acceleration/Deceleration Rates
4- Selecting safe Speed
…
Simply all driving decisions are based on their vision
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Vertical Field of Vision
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75 Deg.
60 Deg.
Line of Sight
3-10 Deg.
Acute vision cone
10 - 12 Deg.
Clear vision cone

Field of Vision: Examples
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5 Deg. (Diameter)
10 Deg.

Horizontal Field of Vision
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90-100 Deg.
60 Deg.

Horizontal Field of Vision
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Binocular Vision
~ 120 Deg.
60 Deg.
Monocular
Vision
~ 35 Deg.
Monocular
Vision
~ 35 Deg.

Field of Vision Characteristics
Impact of Speed on Visual Field:
As speed increases, the visual field decrease significantly, especially
the peripheral vision.
Example:
at 20 mph it becomes 100 deg.
at 60 mph it becomes 40 deg.
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Field of Vision: Impact of Speed (24 km/hr)
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CONEN 442 Transportation Engineering S2021 17

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Field of Vision: “Importance”
Traffic Engineers Use Field of Vision for:
1. Traffic signs placement on highways
2. Traffic signs size
3. Safety analysis
Note: peripheral vision has the most important role in driver’s
speed perception
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Drivers’ Perception
Reaction Time
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Perception- Reaction Time (PRT)
Perception Time:
Can be defined as the time it takes a driver to sense, perceive,
and understand the existence and nature of a stimulus
Reaction Time:
Can be defined as the time it takes a driver to make a
response decision based on the nature of the existing stimulus
and his own state, and to execute that decision.
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Design Values:
2.5 seconds for most computations involving braking reactions. (90th %) (AASHTO)
1.0 second for signal timing purposes (85th %)(ITE)
NOTE: Higher values of PRT for more complex situations might be used (AASHTO)
AASHTO - American Association of State Highway and Transportation Officials
ITE – Institute of Traffic Engineers
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Factors Affecting Driver’s PRT :
1 – Age
2- Fatigue
3- Complexity of the situation
4 – Presence of Alcohol or Drugs in the driver’s
body
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Pedestrians Characteristics:
Walking Speed
Gap Acceptance
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Pedestrian Characteristics
Walking Speed:
1.22 m/s (4 ft/s) Recommended for Intersection Design (15 % Percentile )
accommodates 85%
1.5 m/s ( 5 ft /s) 50Th Percentile (Median)
Gap Acceptance:
Gap acceptance is defined as the acceptable distance gap between two
successive vehicles in a traffic stream the pedestrian is trying to cross.
Depends on:
 perception of approaching vehicle speed
 number of lanes & lane width
 age & gender of pedestrian.
Recommended Design Value:
37.5 m (125 ft ) 85th percentile
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Characteristics
of Traffic System
Elements:
Vehicles:
• Classification
• Turning
• Stopping
• Climbing
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Vehicles Size Characteristics:
ASSHTO Categories:
Passenger Cars
Buses
Trucks
Recreational Vehicles (RV)
AASHTO also defined 20 design vehicles under these categories
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Vehicle Categories (AASHTO):
 Passenger cars:
all passenger cars, SUVs, minivans, vans, and pickup trucks.
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 Buses:
intercity motor coaches, transit buses, school buses, and articulated buses
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Intercity Bus Transit Bus
Van/Small Bus Articulated Bus
School Bus

 Trucks:
single-unit trucks, tractor-trailer, and tractor-semi-trailer combination vehicles
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 Recreational vehicles
motor homes, cars with various types of trailers (boat, campers, motorcycles, etc.)
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Motor Homes
Camper Trailer
Boat Trailer
JetSki Trailer

Low Speed Turning Characteristics
Low Speed Turning is governed by vehicle geometry.
Each design vehicle has the following critical attributes:
1. The minimum inner turning radius
2. Wheelbase width
3. The minimum outer turning radius
4. Path of front overhang
These attributed must be taken into consideration in the
geometric design of traffic facilities
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 Example: W40 (Semi-trailer truck)
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 Application Example for Low Speed Turning Characteristics:
Accommodation of Bus at Signalized Intersection
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 Application Example for Low Speed Turning Characteristics:
Accommodation of Truck at Signalized Intersection
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High-Speed Turning Characteristics
Relationship between Turning Speed, Radius of Curve, Superelevation, and Side
Friction:
Where ,
V – Vehicle Speed (m/s) ,
R- Curve Radius (m),
- Side Friction Coefficient
– Super elevation % ,
– Gravitational Acceleration(m/s2)
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0.01 + =
100
e
R
C.G.

Side Friction:
Side friction is affected by surface condition and vehicle speed.
For design purpose, wet condition is usually assumed. The following
table shows recommended values:
Note: 1 mile = 1.61 Km
Super elevation:
Typical range 0.5-12 % , but in most cases it does not exceed 8%
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Example:
Given the design speed for a highway , to be 120 km/hr. Please determine
the minimum radius for a horizontal curve, if the super elevation was
limited to be 3% & 8%.
Answer: e+f = v2/gR 120kph  120/3.6=33.33 m/s
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Vehicles Stopping Characteristics:
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Vehicle Stopping Characteristics
When a driver sees a hazard, he will press the brake to stop the
vehicle and avoid collision:
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The driver
sees the
hazard
Driver
Starts
Brake
Driver
Crash
Here
Decision Making Distance (d1)
Perception/Reaction Distance
d1 = *
Braking Distance (d2)
d2 =
Total Stopping Distance: ds = d1 + d2
Vi
Friction F = W*f= mg*f
Vf
Vi

Vehicle Stopping Characteristics
Total Stopping Sight Distance (Generic Units):
Where,
ds : Total Stopping Distance (m)
Vi : Initial Vehicle Speed (m/s)
Vf : Final Vehicle Speed (m/s)
g : Gravitational Acceleration (m/s2)
f : Pavement Longitudinal Friction Coefficient (0.348)
G : Vertical Grade %
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= +
= +
= ∗ +
−
2 ( ± 0.01 )

Vehicle Characteristics:
Traffic Light Application (General)
Yellow Time (Y):
All Red Time (AR) (Clearance Time):
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



 

2
Speed
Passing
Speed
Approach
Distance
Sight
Stopping
Y
Speed
Passing
Length
Vehicle
Distance
Passing
AR



Traffic Light Application
For Through Movement (TH) case:
The passing speed is the same as the approach speed, hence:
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V
SSD
Speed
Approach
Distance
Sight
Stopping
Y 

V
L
Width
Speed
Approach
Length
Vehicle
Distance
Passing
AR




V V
Width L
Stopping Sight Distance
(SSD)

V
R
LArc
Stopping Sight Distance
(SSD)
L
Traffic Light Application
For Left Turn Movement (LT) case:
The passing speed for the vehicle is the safe turning speed (Vt),
hence:
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




 






 

2
2
t
V
V
SSD
Speed
Turning
Speed
Approach
Distance
Sight
Stopping
Y
t
Arc
V
L
L
Speed
Passing
Length
Vehicle
Distance
Passing
AR



 gravity
g
on
SideFricti
f
TurnRaduis
R
f
R
g
V
l
l
t



 *
*

Vehicle Characteristics: Applications
Example:
For the shown intersection, please do the following:
For Through Movement (TH) Determine the Yellow time (Y) & Clearing
time (AR)
For Left Turn Movement (LT) Determine the Yellow time (Y) & Clearing
time (AR
Given:
Longitudinal skid friction coefficient = 0.348
Turning Radius (R) = 50 m
Lane width = 3.60 m, Median Width = 4 m
Approach Speed (V)= 60 km/hr ,
Assume Arc length for LT (LArc) =35 meters.
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R
q 45
LArc

Example : Chapter 2
2.2
A driver traveling at 100 km/h rounds a curve on a
level grade to see a truck overturned across the
roadway at a distance of 120 m. If the driver is able to
decelerate at a rate of 0.31g , at what speed will the
vehicle hit the truck? Plot the result for reaction times
ranging from 0.50 to 5.00 s in increments of 0.5 s.
Comment on the results.
2.7
What minimum radius of curvature may be designed
for safe operation of vehicles at 110 km/h if the
maximum rate of superelevation (e) is 6% and the
maximum coefficient of side friction (f) is 0.10? ElDessouki
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Characteristics
of Traffic System
Elements:
Traffic Stream
Characteristics
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Types of Traffic Streams:
Uninterrupted:
Uninterrupted flow facilities have no external
interruptions to the traffic stream. Pure uninterrupted
flow exists primarily on freeways, where there are no
intersections at grade, traffic signals, STOP or YIELD
signs, or other interruptions external to the traffic
stream itself.
Interrupted:
Interrupted flow facilities are those that incorporate
fixed external interruptions into their design and
operation. The most frequent and operationally
significant external interruption is the traffic signal.
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Traffic Stream Parameters
Macroscopic Parameters:
1. Volume or Flow Rate
2. Speed
3. Density
Microscopic Parameters:
1. Headway
2. Spacing
3. Speed of individual vehicles
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Traffic Stream Characteristics:
Macroscopic Parameters:
 Volume or Flow Rate
 Speed
 Density
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Macroscopic Parameters: Volume
Traffic Volume or Flow Rate:
Defined as the number of vehicles passing a point
on a highway, or a given lane or direction of a
highway, during a specified time interval.
Units: Vehicle / Time (hr, day, week , or year )
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Macroscopic Parameters: Daily Volumes
Average annual daily traffic (AADT):
The average 24-hour volume at a given location over a full 365-day year;
the number of vehicles passing a site in a year divided by 365 days.
Average annual weekday traffic (AAWT):
The average 24-hour volume occurring on weekdays over a full 365-day
year; the number of vehicles passing a site on weekdays in a year
divided by the number of weekdays (usually 260).
Average daily traffic (ADT):
The average 24-hour volume at a given location over a defined time
period less than one year; a common application is to measure an ADT
for each month of the year.
Average weekday traffic ( AWT):
The average 24-hour weekday volume at a given location over a defined
time period less than one year; a common application is to measure an
AWT for each month of the year.
NOTE:
Usually these values are in (veh./day) and non-directional
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Macroscopic Parameters: Daily Volumes
Typical Usage for Daily Volumes are:
 Network Planning & Design.
 Feasibility assessment for major projects.
 Prioritization of maintenance projects.
 Assessment of current Demand
 Estimating Transportation trends and forecasting
future demand.
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Macroscopic Parameters: Daily
Volumes Example
 Calculate: AADT & AAWT
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Macroscopic Parameters: Hourly
Volumes
Daily traffic volumes ( ADT, AADT, ..etc) , are useful
for planning purposes but it can not be used for
design and operation of traffic facilities.
Why?
Because traffic volume varies significantly over the
24 hrs of the day, and the direction. Traffic facilities
must be designed to accommodate peak traffic
volume in the peak direction.
Therefore, for design:
We use the DDHV (Directional Design Hourly Volume) ElDessouki
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Macroscopic Parameters: DDHV
Estimation of DDHV
DDHV = AADT * K * D
Where,
AADT : Annual Average Daly Traffic Volume
K : Proportion of the traffic volume occurring during peak hour
D : Direction Proportion
Remember:
AADT is not directional, i.e. traffic flow on both direction of the road is counted
Question:
Why we don’t just count hourly volume and do our design?
Answer:
We usually do our design for future forecast volume. Most future demand forecasting is
carried out in terms of AADT
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Macroscopic Parameters: Peak Hour
Factor
Example showing a synthetic hourly traffic volume pattern for a weekday
in Jazan city
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0
100
200
300
400
500
600
700
800
900
12:00 AM 6:00 AM 12:00 PM 6:00 PM 12:00 AM
Traffic
Volume
(
veh/hr)
Time of Day (hrs)
Morning Peak Hour Afternoon Peak Hour
Average Daily Volume

Factor
Peak Hour:
Is defined as the single hour of the day that has the highest traffic flow
rate.
Estimating Peak Hour Factor (PHF):
1- Traffic volume is counted during the peak hour time frame in 15
minutes increments for a period of 2 hrs.
2- Identify the maximum consecutive 15 min intervals where the traffic
volume is the highest, this would be the Peak Hour
3- Add the traffic volume for the four intervals to get the hourly rate,
then
Where,
V – Hourly volume observed during peak hour
Vmax15 – The maximum volume counted during the 15 minutes intervals
of the peak hour
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=
( )
4 ∗

Factor
Example for Calculating PHF:
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Time Interval Traffic Volume
6:30 – 6:45 423
6:45 – 7:00 563
7:00 – 7:15 635
7:15 – 7:30 745
7:30 – 7:45 865
7:45– 8:00 825
8:00 – 8:15 725
8:15 – 8:30 710

Macroscopic Parameters: Speed
Time Mean Speed ( TMS):
The average speed of all vehicles passing a point on a highway
or lane over some specified time period.
Space Mean Speed (SMS):
The average speed of all vehicles occupying a given section of
highway or lane over some specified time period.
Where,
n – number of observed vehicles
vi - Speed of vehicle i passing the observation station
d - length of traversed highway section
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n
v
n
t
d
TMS
n
i
i
n
i i

 








 1
1















 

n
i
i
n
i
i t
nd
n
t
d
SMS
1
1

Macroscopic Parameters: Speed
Example
Veh. d (m) time(sec) Speed (m/sec)
1 500 10.4 48.08
2 500 6.6 75.76
3 500 8.2 60.98
4 500 9.4 53.19
5 500 10.3 48.54
6 500 6.1 81.97
7 500 11.8 42.37
8 500 6.1 81.97
Sum= 68.9 492.85
TMS = 61.61
SMS = 58.06
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Observations:
SMS are usually less than the TMS
SMS accounts for slower vehicle more than
the TMS
SMS considers the time vehicles occupy
the road

Macroscopic Parameters: Density
Traffic Density (D):
Defined as the number of vehicles occupying a
given length of highway or lane, generally expressed
as vehicles per km or vehicles per km per lane.
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Traffic Stream Characteristics:
Microscopic Parameters:
 Headway
 Spacing
 Speed of individual vehicles
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Microscopic Parameters: Spacing &
Headway
Spacing (da):
Is defined as the distance between successive vehicles in a
traffic lane, measured from some common reference point on
the vehicles, such as the front bumper or front wheels.
 Then density (D) would be:
Headway (ha):
Is defined as the time interval between successive vehicles as
they pass a point along the lane, also measured between
common reference points on the vehicles.
 Then , flow rate (q) would be:
 Average Speed (v ) would be:
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a
d
km
veh
D
1000
)
/
( 
a
h
hr
veh
q
3600
)
/
( 
)
/
(
*
6
.
3
)
/
( a
a h
d
D
q
hr
km
v 


Relationship Between:
Flow Rate, Speed &Density
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Density
D
Speed
v
FlowRate
Q
Where
D
v
Q
s
S




,
*
Flow
Rate
Q
(veh/lane/hr)
Density
D (veh/lane/km)
Jam
Density
Critical
Density
0
Saturation Flow Rate
Congested
Flow
Stable
Flow
0
Free Flow
Speed

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Density
D
Speed
v
FlowRate
Q
Where
D
Q
v
s
s




,
/
Flow Rate
Q (veh/lane/hr)
Speed
v (km/hr)
0
Saturation Flow Rate
Congested
Flow
Stable
Flow
0
Free Flow
Speed

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Density
D
Speed
v
FlowRate
Q
Where
D
Q
v
s
s




,
/
Density
D (veh/lane/km)
Speed
v (km/hr)
0
0
Free Flow
Speed
Jam
Density
speed
flow
free
v
D
D
v
v
f
jam
f










 1
*
Greenshield’s Model(1934):
Constant
Model
C
D
D
C
v
jam









 ln
*
Greenberg’s Model(1959):
eed
FreeFlowSp
v
e
v
v
f
D
D
f
jam










*
Underwood’s Model(1961):
Speed/Density Models:

Characteristics
of Traffic System
Elements:
Traffic Control
Devices
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Traffic Control Devices:
Traffic control devices are the media by which traffic engineers
(communicate with drivers. Virtually every traffic law, regulation, or
operating instruction must be communicated through the use of
devices that fall into three broad categories:
 Traffic markings
 Traffic signs
 Traffic signals
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Traffic Control Devices: MUTCD
Manual on Uniform Traffic
Control Devices (MUTCD)
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Traffic Control Devices: MUTCD
MUTCD define the Purpose of Traffic Control Devices:
“to promote highway safety and efficiency by providing
for orderly movement of all road users on streets and
highways, throughout the Nation.”
MUTCD define also the five requirements for a traffic
control device to be effective in fulfilling that mission:
1. Fulfill a need
2. Command attention
3. Convey a clear, simple message
4. Command respect of road users
5. Give adequate time for a proper response
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MUTCD Core Contents
1. Detailed standards for the physical design of the device,
specifying shape, size, colors, legend types and sizes, and
specific legend.
2. Detailed standards and guidelines on where devices should be
located with respect to the traveled way.
3. Warrants, or conditions, that justify the use of a particular
device.
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MUTCD Core Contents: Examples
1. Detailed standards for the
physical design of the
device, specifying shape,
size, colors, legend types
and sizes, and specific
legend.
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2. Detailed standards and guidelines on where
devices should be located
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3. Warrants, or conditions, that justify the use of a
particular device.:
STOP control Warrants (MUTCD 2009) :
Guidance: At intersections where a full stop is not necessary at all
times, consideration should first be given to using less restrictive
measures such as YIELD signs
The use of STOP signs on the minor-street approaches should be
considered if engineering judgment indicates that a stop is always
required because of one or more of the following conditions:
I. The vehicular traffic volumes on the through street or highway exceed 6,000
vehicles per day;
II. A restricted view exists that requires road users to stop in order to adequately
observe conflicting traffic on the through street or highway; and/or
III. Crash records indicate that three or more crashes that are susceptible to
correction by the installation of a STOP sign have been reported within a 12-
month period, or that five or more such crashes have been reported within a 2-
year period. Such crashes include right-angle collisions involving road users on the
minor-street approach failing to yield the right-of-way to traffic on the through
street or highway.
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MUTCD : Traffic Signs
Types of Traffic Signs:
 Regulatory signs. Regulatory signs convey
information concerning specific traffic regulations.
Regulations may relate to right-of-way, speed limits,
lane usage, parking, or a variety of other functions.
 Warning signs. Warning signs are used to inform
drivers about upcoming hazards that they might not
see or otherwise discern in time to safely react.
 Guide signs. Guide signs provide information on
routes, destinations, and services that drivers may
be seeking.
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 Regulatory signs. Regulatory signs convey information
concerning specific traffic regulations.
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 Regulatory signs. Regulatory signs convey information
concerning specific traffic regulations.
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 Guide signs. Guide signs provide information on
routes, destinations, and services that drivers may
be seeking.
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 Guide signs. Guide signs provide information on routes,
destinations, and services that drivers may be seeking.
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MUTCD : Pavement Markings
Types of Pavement Markings:
Longitudinal markings
Transverse markings
Object markers and delineators
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Longitudinal
markings:
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Longitudinal
markings:
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Longitudinal
markings:
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Longitudinal
markings:
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Transverse markings:
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Roundabout Markings:
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Roundabout
Markings:
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Roundabout
Markings:
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MUTCD : Traffic Signals
:
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MUTCD Warrants for Signalized Intersection:
Warrant 1, Eight-Hour Vehicular Volume
Warrant 2, Four-Hour Vehicular Volume
Warrant 3, Peak Hour
Warrant 4, Pedestrian Volume
Warrant 5, School Crossing
Warrant 6, Coordinated Signal System
Warrant 7, Crash Experience
Warrant 8, Roadway Network
Warrant 9, Intersection Near a Grade Crossing

Conen 442 module1a: Elements of Traffic System

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Conen 442 module1a: Elements of Traffic System