OVERVIEW OF HIGHWAY DESIGN Flashcards
A process in Highway Engineering where the most appropriate location, alignment and shape of a highway are selected.
Highway Design
In highway design, the following highway characteristics are encouraged:
- Self-explaining roads
- Roads that encourage safe speeds
- Forgiving roadsides
- Functionality
- Predictability
- Homogeneity
Highway design involves the consideration of five (5) major factors:
- Human Factors and Driver Performance
- Vehicles
- Traffic Characteristics
- Physical Elements
- Economic Factors
Determines how effectively will the drivers be able to use the road.
HUMAN FACTORS AND DRIVER PERFORMANCE
Considerations in traffic characteristics
- Average Daily Traffic (ADT)
- Peak hour traffic
- Directional Distribution
- Composition of traffic
- Projection of future traffic demands
Physical Characteristics to be included in highway design.
- Highway capacity
- Access control and management
- Pedestrians (bus stops, loading areas, stairs)
- Bicycle facilities and environment (Highways should complement
their environment)
Concerned with the cost of a proposed improvement and the benefits
resulting from it.
ECONOMIC FACTORS
A 3D representation of the project site
Topographic Surveys (Topo)
Also called the Horizontal control, is the route of the road, defined as a series of horizontal tangents and curves.
ALIGNMENT
Helps in better decision making when designing highways.
SPATIAL DATA
the total volume of vehicle
traffic on a highway or road for a year divided by 365 days
Annual Average Daily Traffic (AADT)
AADT directly affects highway characteristics such as:
- Pavement thickness
- Level of Service (LOS)
Investigations below the subgrade level.
SUBSURFACE INVESTIGATIONS
For areas with light cut and fill, investigations should be fulfilled with
at least a depth of __________ below the proposed subgrade
1.5 m
An area of land that collects water after rainfall. Water flows down into these areas and collects into rivers and streams.
CATCHMENT AREAS
Necessary for the effective planning and
design of box culverts, bridges and possible outfalls.
EXISTING STREAMS/RIVERS
Necessary especially when the project involves road widening.
EXISTING STRUCTURES AND UTILITY SERVICES
Target speed at which drivers are intended to travel on a street, and not, as often misused, the maximum operating speed.
Design Speed
Expressways should be designed for speeds not less than _______
80 kph
The distance at which a driver of a vehicle can see an object of specified height on the road ahead
Sight Distance
The minimum distance required for avehicle, travelling at the design speed, to stop before reaching an object in its path
Stopping Sight Distance
The distance needed for a driver to detect an unexpected threat, recognize the threat, decide on what to do and initiate a maneuver to avoid the said threat
Decision Sight Distance
The minimum distance required to safely
make a normal passing maneuver on 2-lane highways
Passing Sight Distance
When a vehicle moves in a circular path, it is forced ____________ by centrifugal force which is counterbalanced by the vehicle weight component due to the roadway tires
and surfacing
Radially Outward
