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1. DESIGNING THE
HIGHWAY
MARIA DIANNE L. ABELLA
BSCE 4C

2. CONSISTENCY
Consistency is the most 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:
1. Clear information and guidance through a variety of road signs.
2. Avoiding abrupt changes in the traffic as well as the road standards.

3. Definition of Terms
AASTHO is the American Association of State Highway and Transportation
Officials. In 1914, the American Association of State Highway Officials (AASHO)
was established as an association of State Territorial and District of Columbia
Highway Department, and the Federal Highway Administration.
AASHTO publications includes:
1. Transportation Materials Specifications and Tests
2. Specifications for highway bridges
3. Geometric design standards
4. Numerous policy statements and guides

4. AASHTO publications are authoritative. References are made in these books and
periodic manuals. The association also publishes the ASSHTO quarterly report on current
Highway and Transportations subject including trends in forecast and legislation.
Roads and Highway is 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 which generally used to
describe a public thoroughfare. It can also refer to railways.
Highway. The term was first used in England to describe a public road built by digging
ditches on both sides and heaping up the earth in the middle creating a way higher that
the adjacent land. Highway now connotes, a higher state of development than road, but
the words are almost interchangeable.

5. Expressway is a divided arterial highway for through traffic with full or partial control
or access and generally provided with grade separation a major intersections.
Freeway is an expressway with full control of access.
Control of access 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.

6. 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 crossings at grade and some private driveway connections
allowed.
Through Street or Through Highway – every highway or portion thereof on which
vehicular traffic is given preferential right of way, and at the entrance to which vehicular
traffic from intersecting highways is required by law to yield right of way to vehicles on
such through highway in obedience to either stop sign or yield sign erected thereon.
Parkway is an arterial highway for non-commercial traffic, with full or partial access
usually located within a park or ribbon park-like development.
Arterial Street is an arterial route that carries traffic to the nearest access point or
through traffic. It often serves as the most advantageous routes for relatively long distance
travel. Most arterial streets are existing highways of considerable length along which cross
traffic is regulated by signals or stop signs.

7. Basic Considerations in Planning Arterial
Roadways
1. Selections of the routes
2. Studies of the traffic volume
3. Origin and destination
4. Accident experienced
5. Width should not be less than 15 meters
6. Must carry at least one lane traffic in each directions
7. Should be at least one kilometer in length
8. Should skirt neighborhood areas rather than penetrate them
9. On grid design system streets, arterials are spaced at about 600 to 900 meters
apart
10. Where accident hazard is not a factor, the minimum volume to justify arterial
road is 300 vehicles per average hour during the day, and 450 vehicles hourly
during peak period.

8. Sometimes, peak hour trafficvolume on designated arterial road exceeds the
capacity of two-way streets, and to increase the arterial capacity, the following
solutions are enforced:
1. During peak hours, parking is prohibited on one or both sides of the street
2. Parking is prohibited several meters away from each side of the road
intersection or corners
3. Right turn is allowed on red signals any time with care
4. Left turns are eliminated on congested intersections
5. The direction of traffic is reversed in the center lane to provide more lanes in
the direction of heavier traffic flow.

9. Collector Street from smaller mesh grid pattern where passengers are pick up from
the service streets and carried to the arterials. Large commercial enterprises or
amusement facilities like drive in theaters are mostly fronting arterial roads.
Local Road 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.
Highway Capacity 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 vehicles per
hour.
1. Under ideal conditions, one freeway lane can accommodate about 2,000 passenger cars
per hour
2. Two-lane road can carry up to 1,000 passenger cars per hour in each direction.

10. There is an obvious relationship between vehicle speed and highway capacity. As
the volume of traffic approaches capacity, the average speed is markedly reduced.
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
started on hourly “Observed Traffic Volume” or estimated 30th hour volume commonly
used for design purposes. Some highway agencies use traffic volume for 5 minutes
interval to distinguish short peak movement of vehicles.

11. The Design Speed
There is no single set of Geometric Standards that will apply to all highways. For
every highway segment, decisions regarding appropriate control for each of the many
details or requirements must be addressed individually or separately.
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 speed that can be
maintained over a specified section of the highway when wheater and traffic
conditions are so favorable that the design features of the highway govern.

12. Basic Design Features refers to the tightness and super elevation of curves,
the sight distance, and grade. The design speed is basically higher than the
anticipated average speed. AASHTO recommend that:
“The design speed be set to the greatest degree possible, to satisfy the
needs of nearly all drivers both today and throughout the road anticipated life.”

13. FACILITY
Design Speed
URBAN Km/hr RURAL Km/hr
Freeway 80-95 preferred 110-95 mountainous
Arterial 64-95 but 48 in built up
areas
80-110
Collectors 48 km/hr See table 2.2
Local 32-48 km/hr See table 2.2
TABLE 2.1 MINIMUN RECOMMENDED DESIGN SPEED

14. 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
Local 0-50 50-250 250-400 Over 400
Level 45 45 60 75
Rolling 30 45 45 60
Mountainous 30 30 30 45
TABLE 2.2 AASHTO MINIMUN DESIGN SPEED
KM/HR. FOR RURAL COLLECTORS AND LOCAL ROADS
BASED ON THE CURRENT ADT

15. Cross Section of Typical Highway
The cross section of a typical highway has latitude of variables to consider such as:
1. The volume of traffic
2. Character of the traffic
3. Speed of the traffic
4. Characteristics of motor vehicles and of the driver

16. Highway design usually adopted cross section that is uniform in thickness from end to end of
the improvement. This is acceptable on high volume traffic road facilities. For a low volume traffic
facilities, modification of the features like the shoulders width in rough areas are usually employed
to reduce costs. A cross section design generally offers the expected level of service for safety and
a recent study showed that:
1. A 7.20 meters wide pavement has 18% less accident compared with pavement narrower than
5.50 m. wide.
2. A 7.20 meters wide pavement has 4% fewer accidents than the 6.00 meters wide roadway.
3. Accident records showed no difference between 6.60 meters and the 7.20 meters wide
pavements.
4. For the 6.00 m., 6.60 m. and 7.20 meters wide pavement with 2.70 to 3.00 m. wide shoulder,
recorded accident decreases by 30% compared to 0 to .60 m. wide shoulder. And 20% compared
with a .90 to 1.20 meters wide shoulder.

17. For Two Lane Rural Highway , a 7.20 meters wide surface is required for safe
clearance between commercial vehicles and is recommended for main highways.
For Collector Roadway, 6.00 meters wide surface is acceptable only for low volume
traffic including few trucks travelling thereon.
For Local Rural Roadway, the minimum surface width is 4.80 meters for a 30
km/hr. design speed.
For Urban Roadway, the minimum design width is 3.60 meters although 3.00
meters is allowed where space is limited.

18. Where there are heavy meetings or overtaking between cars and trucks, air disturbances
sometimes cause side collision between passing vehicles when swerved within or out of their lanes.
Motorists are requesting for wider lanes.