CES 341:Transportation Engineering and Planning
Chapter 3
Introduction to Physical Design of
Transportation Facilities
Asst. Prof. Dr. Mongkut Piantanakulchai
Email: mongkut@siit.tu.ac.th
1
3.1 The Design Process

Overall process of transportation project
development include
•Technical elements
•Legal elements
•Political elements


When carried out of public agency, it
must balance the interest of stakeholders
The Planning and Design process
CES 341 Transportation
Engineering and Planning
Chapter3: Introduction to Physical Design of
Transportation Facilities
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3-1 The
transportation
facility design
process
CES 341 Transportation
Engineering and Planning
Chapter3: Introduction to Physical Design of
Transportation Facilities
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3.2 Design Standards

Standards by type of facility
• Highway– design standards by state DOT,
recommended standards by AASHTO, FHWA
• Railway – design standards by railroad company or
transit authority, recommended standards by AREA
• Air – design standards for airport landing areas by
FAA (in the US), ICAO (for international level)

Design standards should also consider human
capabilities characteristics. In many cases, the
design standard is based on comfort
CES 341 Transportation
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Chapter3: Introduction to Physical Design of
Transportation Facilities
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Table 3.1: Relationships between vehicular
and facility characteristics (1/2)
Vehicular characteristics
Related facility characteristics
Length
Park stall length
Transit station platform length
Width
Lane width
Parking stall width
Lateral clearance
Height
Vertical clearance
Minimum vertical curve length
Wheelbase (turning radius)
Lateral clearance on curves
Intersection edge radii
CES 341 Transportation
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Chapter3: Introduction to Physical Design of
Transportation Facilities
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Table 3.1: Relationships between vehicular
and facility characteristics (2/2)
Vehicular characteristics
Related facility characteristics
Weight
Structural design of surface
Structural design of guideway
Structural design of bridges
Acceleration/deceleration
Maximum grade
Minimum vertical curve length
Horizontal curve radius
Speed
Horizontal curve radius
Minimum vertical curve length
Maximum superelevation
Lift
Runway length
CES 341 Transportation
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Chapter3: Introduction to Physical Design of
Transportation Facilities
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3.3 Design Speed and Sight Distance

Design speed (for highways): The
maximum safe speed that can be maintained over a
specified section of highway
CES 341 Transportation
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Chapter3: Introduction to Physical Design of
Transportation Facilities
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Table 3.2: Recommended Design Speeds
Conditions
Design speed, km/h
Limited access types
Rural freeways in mountainous terrain
Freeways in urban areas
80-100
100-110
Rural freeways, level terrain
110
Unlimited access types
Rural arterials:
Flat terrain
100-110
Rolling terrain
80-100
Mountainous terrain
60-80
Urban:
Arterial streets
60-100
Arterial streets, central business districts
50-60
Source: Based on A Policy on Geometric Design of Highways and Streets. Copyright 1994
CES 341 Transportation
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Chapter3: Introduction to Physical Design of
Transportation Facilities
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Stopping Sight Distance (SSD)


Stopping sight distance = distance required for
vehicle to stop safely under assumed conditions (such
as height of object, driver’s eye’s height, etc.)
Stopping sight distance formula
s  d r  db
(3.1)
s = stopping sight distance
dr = perception-reaction distance
db = breaking distance
CES 341 Transportation
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Chapter3: Introduction to Physical Design of
Transportation Facilities
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Perception-Reaction Distance

Perception-reaction distance formula
d r  vtr
(3.2)
dr = perception-reaction distance
v = design speed
tr = perception-reaction time

AASHTO recommended conservative tr value
of 2.5 sec for stopping decision
CES 341 Transportation
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Chapter3: Introduction to Physical Design of
Transportation Facilities
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Breaking Distance

Breaking distance simplified formula
2
v
db 
2g f  G
(3.3)
db
g
f
= breaking distance
= acceleration of gravity
= coefficient of friction between tires and
pavement
G
= average grade, dimensionless ratio (m/m)
CES 341 Transportation
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Chapter3: Introduction to Physical Design of
Transportation Facilities
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Breaking Distance


For cases in which G
varies (for instance,
in a vertical curve),
an average value for
the entire break
reaction distance is
used)
AASHTO also gives
the mixed unit
formula
CES 341 Transportation
Engineering and Planning
v2
db 
254 f
(3.3a)
db = breaking distance (m)
v = design speed (kph)

Note that the effect
of grade is ignored
in this formula
Chapter3: Introduction to Physical Design of
Transportation Facilities
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Table 3.3: Coefficients of friction and
stopping sight distances
Design speed, km/h
Coefficient of friction f
Stopping sight distance, m
30
0.40
29.6-29.6
40
0.38
44.4-44.4
50
0.35
57.4-62.8
60
0.33
74.3-84.6
70
0.31
94.1-110.8
80
0.30
112.8-139.4
90
0.30
131.2-168.7
100
0.29
157.0-205.0
110
0.28
179.5-246.4
120
0.28
202.9-285.6
Source: Based on A Policy on Geometric Design of Highways and Streets. Copyright 1994
CES 341 Transportation
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Chapter3: Introduction to Physical Design of
Transportation Facilities
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Passing Sight Distance (PSD)
Figure 3.2: Elements of passing sight distance
CES 341 Transportation
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Chapter3: Introduction to Physical Design of
Transportation Facilities
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Table 3.4: Passing sight distances
Design speed, km/h
Passing sight distance, m
30
217
40
285
50
345
60
407
70
482
80
541
90
605
100
670
110
728
120
792
Source: Based on A Policy on Geometric Design of Highways and Streets. Copyright 1994
CES 341 Transportation
Engineering and Planning
Chapter3: Introduction to Physical Design of
Transportation Facilities
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3.4 Design Documents For
Transportation Projects

Bid documents

Basic elements of standard plans
• Plans
• Specifications
• Estimates
• Plan
• Profile
• Cross section
• Superelevation diagram
CES 341 Transportation
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Chapter3: Introduction to Physical Design of
Transportation Facilities
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Figure 3.3: Highway plan view
CES 341 Transportation
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Chapter3: Introduction to Physical Design of
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Figure 3.3: Highway profile and superelevation diagram
CES 341 Transportation
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Chapter3: Introduction to Physical Design of
Transportation Facilities
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Some technical terms







Profile grade
Stations
Tangents
Elevations
Grades
Cross-slopes
Standard specifications, special provisions,
general clauses, other clauses
CES 341 Transportation
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Chapter3: Introduction to Physical Design of
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Problem 3.1

Determine the minimum stopping sight
distance on a *2.5% grade at a design
speed of 90 km/h.
CES 341 Transportation
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Chapter3: Introduction to Physical Design of
Transportation Facilities
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Problem 3.1 (solution)
Total required stopping sight distance
s  dr  db
Reaction distance
 1,000m km 
2.5s   62.5m
d r  vtr  90km h 
 3,600s h 
Braking Distance
f  0.30 (Table 3.3)
G   0.025 (given)
2

 1,000m km 


90km h 

v2
 3,600s h 

db 

 116.0m
2g f  G
2 9.8m s 2 0.30  0.025


Total sight distance
s  dr  db  62.5  116. 0  178.5 m
CES 341 Transportation
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Chapter3: Introduction to Physical Design of
Transportation Facilities
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Problem 3.2

Determine the minimum stopping sight
distance on a +1.5% grade at a design
speed of 100 km/h.
CES 341 Transportation
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Chapter3: Introduction to Physical Design of
Transportation Facilities
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Problem 3.2 (solution)
Total required stopping sight distance
s  dr  db
Reaction distance
 1,000m km 
2.5s   69.4m
d r  vtr  100km h 
 3,600s h 
Braking Distance
f  0.29 (Table 3.3)
G   0.015 (given)
2

 1,000m km 


100km h 

v2
 3,600s h 

db 

 129.1m
2g f  G
2 9.8m s 2 0.29  0.015


Total sight distance
s  dr  db  69. 4  129.1  198.5 m
CES 341 Transportation
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Chapter3: Introduction to Physical Design of
Transportation Facilities
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Problem 3.3

Determine the minimum stopping sight
distance on a *4.0% grade at a design
speed of 70 km/h.
CES 341 Transportation
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Chapter3: Introduction to Physical Design of
Transportation Facilities
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Problem 3.3 (solution)
Total required stopping sight distance
s  dr  db
Reaction distance
 1000m km 
2.5s   48.6m
d r  vtr  70km h 
 3600s h 
Braking Distance
f  0.31 (Table 3.3)
G   0.04 (given)
2

 1,000m km 


70km h 

2
3
,
600
s
h
v


db 

 71.4m
2
2g  f  G
2 9.8m s 0.31  0.04


Total sight distance
s  dr  db  48. 6  71. 4  120. 0 m
CES 341 Transportation
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Chapter3: Introduction to Physical Design of
Transportation Facilities
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Exercise 3.1

Design standards link vehicle characteristics,
human characteristics, and the characteristics
of the transportation facility. What features of
human and vehicle characteristics are
important in the derivation of design
standards?
CES 341 Transportation
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Chapter3: Introduction to Physical Design of
Transportation Facilities
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Exercise 3.1 (Solution)

Human characteristics that
are important in the
derivation of design
standards include visual
ability, ability to hear,
reaction times, gap
acceptance behavior,
steering behavior, and the
subjective sense of comfort.
CES 341 Transportation
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
Vehicular characteristics
that are important in the
derivation of design
standards include physical
dimensions (length, width,
height, and wheelbase),
weight (gross weight and
wheel loads), acceleration
and deceleration
characteristics, maximum
speed, and (for aircraft only)
lift.
Chapter3: Introduction to Physical Design of
Transportation Facilities
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Exercise 3.2

List and briefly describe at least five
transportation facility characteristics
typically specified by design standards.
CES 341 Transportation
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Chapter3: Introduction to Physical Design of
Transportation Facilities
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Exercise 3.2 (Solution)

Any five of the following:

Minimum radius of horizontal
curve. For a given design
speed, minimum curve radius
is limited by maximum
allowable side friction, which is
usually based on a comfort
standard; maximum
superelevation rate (or
banking) for the curve; and the
necessity to maintain stopping
sight distance.
CES 341 Transportation
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
Maximum rate of superelevation.
For
highways,
maximum
superelevation rate is limited
by side friction and by presence
of roadside features such as
driveways. For railways, it is
limited by the need to limit
imbalances in the loads on the
rails.
Chapter3: Introduction to Physical Design of
Transportation Facilities
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Exercise 3.2 (Solution)



Maximum
grade.
Maximum
upgrades are limited by vehicle
power/weight ratios and vehicle
traction. Maximum downgrades
are also limited by stopping
distances and sight distances.
Minimum grades for some types of
highway are limited by the need to
provide drainage.

Minimum cross-slopes for highways,
runways, and taxiways are limited
by the need to provide drainage.
Minimum length of vertical curve.
For highways minimum length of
vertical curve is limited by stopping
or
passing
sight
distance
requirements, vertical acceleration,
and appearance standards.
For
railways, minimum length of
vertical curve is also limited by the
need to prevent jerk on couplings in
sag vertical curves. For runways
and taxiways, minimum length of
vertical curve is limited by sight
distance requirements.

CES 341 Transportation
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Chapter3: Introduction to Physical Design of
Transportation Facilities
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Exercise 3.2 (Solution)


Edge radii in roadway and taxiway
intersections are limited by
vehicle turning radii. These, in
turn, are related to vehicle
wheelbase dimensions.
Minimum intersection setbacks
(minimum
distances
to
obstructions to vision) are
limited by stopping sight
distance and driver gapacceptance behavior.
CES 341 Transportation
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

Freeway ramp junction details are
limited
by
gap-acceptance
behavior, steering behavior in
entering or exiting lanes, and
vehicle
acceleration
and
deceleration capabilities
Horizontal and vertical clearances
are
limited
by
vehicle
dimensions and in the case of
horizontal
clearances
for
highways, by the need to
provide clear recovery zones
for vehicles that run off the
road.
Chapter3: Introduction to Physical Design of
Transportation Facilities
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Exercise 3.3

Four basic elements of facility plans document
the geometry of linear transportation facilities
such as highways and railways. List and
briefly describe these four elements.
CES 341 Transportation
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Chapter3: Introduction to Physical Design of
Transportation Facilities
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Exercise 3.3 (Solution)
The plan view (or simply "plan").
This is a drawing of the facility as
it would look to an observer
directly above it.
The profile. This drawing has
elevation as its vertical axis, and
horizontal distance, as measured
along the centerline of the facility
(or other recognized reference
line), as its horizontal axis.
The geometric cross-section. This
view has elevation as its vertical
axis and horizontal distance,
measured perpendicular to the
centerline, as its horizontal axis.
CES 341 Transportation
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The superelevation diagram. This
applies to curved facilities, such as
highways or railways, only. It
consists of a graph with roadway
or railway cross-slope (vertical
axis) versus horizontal distance
(horizontal axis). The cross-slope
is measured relative to the
centerline or some other axis of
rotation for the facility.
Alternatively, the diagram may
show the elevation of the edge of
pavement on the vertical axis.
Chapter3: Introduction to Physical Design of
Transportation Facilities
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Computer Exercise
3.1 Spread sheet. Use a spread sheet to construct
a table of stopping sight distances for design
speeds ranging from 30 km/h to 120 km/h in
increments of 10 km/h and grades ranging
from 6% to +6% in 2% increments.
CES 341 Transportation
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Chapter3: Introduction to Physical Design of
Transportation Facilities
34
Worksheet
km/h -> m/s factor =
Acceleration of gravity =
Reaction time =
0.277778
9.8
2.5
Grade
Speed,
km/h
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
110.00
120.00
f
0.40
0.38
0.35
0.33
0.31
0.30
0.30
0.29
0.28
0.28
CES 341 Transportation
Engineering and Planning
-0.06
31.25
47.46
68.66
94.16
125.77
160.54
195.37
240.61
292.91
341.01
-0.04
30.68
46.30
66.47
90.54
120.06
152.46
185.15
226.91
274.87
319.54
-0.02
30.16
45.27
64.55
87.38
115.13
145.54
176.38
215.25
259.60
301.37
0.00
29.69
44.35
62.84
84.61
110.84
139.54
168.79
205.19
246.51
285.80
0.02
29.27
43.52
61.32
82.16
107.07
134.29
162.15
196.44
235.17
272.30
Chapter3: Introduction to Physical Design of
Transportation Facilities
0.04
28.89
42.77
59.96
79.97
103.73
129.66
156.29
188.74
225.25
260.49
0.06
28.54
42.09
58.73
78.01
100.75
125.54
151.08
181.92
216.49
250.07
35
Worksheet
Notes
Cell names
$D$1
$D$2
$D$3
fac
grav
t
Column names for table
Speed column
F column
Grade columns
v
f
G
Formula for cells in table is
=v*fac*t+((v*fac)^2/((2*grav)*(f+G)))
CES 341 Transportation
Engineering and Planning
Chapter3: Introduction to Physical Design of
Transportation Facilities
36