CE 108
HIGHWAYS
AND
RAILROAD
ENGINEERIN
G ENGR. GIAN CARLO B. DUL
Module
3.1
Designin • Consistency
g the • Definition of Terms
Highway • Design Speed
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ENGR. GIAN CARLO B. DUL
Consistency
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ENGR. GIAN CARLO B. DUL
Consistency
• Consistency is the most important single rule in highway design. That is, by making
every element of the roadway conforms to the expectation of every driver.
Drivers expect the highway agency to provide them with;
• Clear information and guidance through the variety of road signs.
• Avoiding abrupt changes in the traffic as well as the road standards.
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Definition of
Terms
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ENGR. GIAN CARLO B. DUL
AASHTO
• AASHTO (American Association of State Highway and Transportation Officials)
• Their task is to prepare specification manual and standards, representing the
current highway engineering practice.
AASHTO publications include;
• Transportation Materials Specifications and Tests
• Specifications for Highway Bridges
• Geometric Design Standards
• Numerous Policy Statements and Guides
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Definition of Terms
• Roads and Highways
• Defined as strips of land that have been cleared and further improved for
the movement of people and goods.
• Road
• Road has somewhat broader application in usage while generally used to
describe a public thoroughfare. It can also refer to railways.
• Highway
• A higher state of development than road, but the words are almost
interchangeable.
• Expressway
• It is a divided arterial highway for through traffic with full or partial control or
access and generally provided with grade separation at major intersections.
• Freeway
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• It is an expressway with full control of access.
Definition of Terms
• Control of Access
• It is a condition where the rights of owners or occupants of adjoining land or other
persons access to light, air or view in connection with a highway is fully or partially
controlled by public authority.
• Full Control of Access
• The authority to control access is exercised to give preference to through traffic by
providing access connections to selected public roads only. Crossing at grade or
direct private driveway connections is not permitted.
• Partial Control of Access
• The authority to control access is exercised to give preference to through traffic.
Although in addition to access connections with selected public roads, there may
be some crossing at grade and some private driveway connections allowed.
• Arterial Street
• It is an arterial route that carries traffic to the nearest access point or through
traffic. Arterial street is considered as a “make do” substitute for controlled access
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facilities when traffic volume exceeds about 20,000 vehicles per day.
Definition of Terms
• Collector Street
• Form smaller mesh grid pattern where passengers are pick up from service streets
and carried to the arterial. Large commercial enterprises or amusement facilities like
drive in theaters are mostly fronting arterial roads.
• Local Road
• It is defined as street or road primarily for access to residence, business or other
adjoining properties. It is also defined as a road constructed and maintained by the
local government.
• AADT or ADT
• Refers to traffic volume or flow on a highway as measured by the number of vehicles
passing a partial station during a given interval of time. It is called “Average Annual
Daily Traffic” if the period is less than one year. Volume may be stated on hourly
“Observed Traffic Volume” or estimated 30th hour volume commonly used for design
purposes.
• Highway Capacity
• It is defined as the maximum number of vehicles that are reasonably expected to pass 9
Basic Consideration in Planning Arterial
Roadways
• Selection of the routes
• Studies of the traffic volume
• Origin and destination
• Accident experienced
• Width should not be less than 15 meters
• Must at least carry one lane of traffic in each direction
• Should be at least one kilometer in length
• Should skirt neighborhood areas rather than penetrate them
• On grid design system streets, arterials are spaced at about 600 to 900
meters apart
• Where hazard is not a factor, the minimum volume to justify arterial road is
300 vehicles per average hour per day and 450 vehicles hourly during peak
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periods
Design Speed
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ENGR. GIAN CARLO B. DUL
Highway Capacity
• It is defined as the maximum number of vehicles that are
reasonably expected to pass a given point over a given period of
time usually expressed as vehicle per hour.
• Under ideal conditions, one freeway lane can accommodate
about 2,000 passenger cars per hour.
• Two-lane roads can carry up to 1,000 passenger cars per hour
in each direction.
• As the volume of traffic approaches capacity, the average speed is
markedly reduced.
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Design Speed
• AASHTO defined Design Speed as;
• The speed determined for design and correlation of the physical feature of a
highway that influence vehicles operation. It is the maximum that can be
maintained over a specified section of the highway when weather and traffic
conditions are so favorable that the design features of the highway govern.
Table 2-1 Minimum Recommended Design Speed
Design Speed
Facility
Urban (kph) Rural (kph)
Freeway 80-95 preferred 110-95 mountainous
Arterial 64-95 but 48 in built up areas 80-110
Collectors 48 See Table 2-2
Local 32-48 kph See Table 2-2
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Design Speed
Table 2-2 AASHTO Minimum Desing Speed
Kilometer/Hour for Rural Collectors and Local Roads Based on Current
ADT
Class Terrain Average Daily Traffic
Collector 0-400 400-750 750-2000 2000-4000 Over 4000
Level 60 75 75 75 90
Rolling 45 60 60 75 75
Mountainous 30 45 45 60 60
Local 0-50 50-250 250-400 Over 400
Level 45 45 60 75
Rolling 30 45 45 60
Mountainous 30 30 30 45 14
Reference
•Elements of Roads and Highways
(Second Edition)
•By Max B. Fajardo, Jr.
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