Lesson 3: 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
6 Characteristics of Highway Design
- 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
Determines what types of vehicles will use the road.
Vehicles
Primarily involves traffic volumes and traffic characteristics.
Traffic characteristics
Concerned with the cost of a proposed improvement and the benefits resulting from it.
Economic Factors
Traffic Characteristics considers (5):
- Average Daily Traffic (ADT)
- Peak hour traffic
- Directional Distribution
- Composition of traffic
- Projection of future traffic demands
4 Elements of Physical Characteristics
- Highway capacity
- Access control and management
- Pedestrians (bus stops, loading areas, stairs)
- Bicycle facilities and environment (Highways should complement their environment)
8 Data needed for highway design
- Field Survey Information (Topo)
- Alignment
- Spatial Data (Barangays, Protected Sites, Ancestral Domains, etc.)
- AADT (Annual Average Daily Traffic)
- Subsurface Investigations
- Catchment Areas (For Cross Drain Design)
- Existing Streams/Rivers
- Existing Structures and Utility Services
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
It is commonly used for identifying spatial data. QGIS is an example of a GIS software.
GIS software
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 2 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 area
Necessary for the effective planning and design of box culverts, bridges and possible outfalls.
Existing streams/rivers
These are necessary especially when the project involves road widening.
Existing structures and utility services
The most efficient alignment
Straight line
target speed at which drivers are intended to travel on a street, and not, as often misused, the maximum operating speed.
Design speed
3 types of terrain
- Level
- Rolling
- Mountainous
Expressways should be designed for speeds not less than _______
80kph
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 a vehicle, 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 radially outward by _________________ which is counter-balanced by the vehicle weight component due to the roadway tires and surfacing
centrifugal force
In superelevation, Centrifugal force is counteracted by the ______________
frictional force
________________ is implemented for roads with 2 lanes.
This is to give allowance for long vehicles to complete a turning maneuver in a curve without falling outside the pavement.
widening of curves
Also called the Profile, they serve as the vertical control
Vertical Alignment
Maximum grades of ___% are considered appropriate for a design speed of _______
5, 110 kph
For a design speed of ________ maximum grades are generally in the range of 7 to 12% depending on topography
50 kph
In the Philippines the maximum grade widely used is ________
6%
On through cut sections grade should be at least _____% to provide longitudinal drainage.
0.50
One of the most common enemy of any highway infrastructure and can infiltrate parts of the highway both from above and below
Water
Water from above can cause erosion of slopes
Storm Water
Water from below can push the pavement up
Water Table
One of the most common software used for drainage design
Storm and Sanitary Analysis (SSA)
The slope of the surface of a pavement measured at right angles to the horizontal alignment
Cross slope or Crossfall
Road drainage should be designed for a ______ flood design capacity, with a check capacity of _____ flood
15 year; 25 year
Minimum flow velocity should be at _____ m/s at pipe full; Maximum velocity to be adopted or piped drainage systems is __ m/s
0.8, 5
Minimum pipe size adopted should be _____ in order to allow the passage of debris and minimize the risk of blockage
910 mm
Three types of pavement found in the Philippines:
- Flexible (orAsphalt pavement)
- Rigid (or Concrete pavement)
- Unbound, gravel surfaced, unsealed or ‘unpaved’ roads
Defined as that portion of the road or highway, placed above the subgrade specifically for the support of and to provide a running surface for vehicular traffic
Pavement
Process of determining the thickness and strength of pavement laid on a soil foundation (subgrade).
Pavement Design
Earthworks
One of the most frequent disturbances in road operation is ________________.
slope failure
