Highway Alignment and Road Classifications

Highway Alignment

• Highway alignment refers to the location of the highway's center line on the earth.
• Highway alignment projections in two planes are referred to as horizontal alignment and vertical alignment, respectively, when they are in the horizontal or vertical directions.
• Key Requirements for Highway Alignment:
  • Safe
  • Economical
  • Short
  • Easy
  • Comfort

Different Road Classifications in the Philippines

• National Primary Roads

  • Directly link major cities with a population of at least 100,000 people.
  • Functions:
    • Connect major cities and urban centers.
    • Facilitate long-distance travel.
    • Support national economic development.

• National Secondary Roads

  • Connect cities to national primary roads, major ports, airports, and tourist service centers.
  • Functions:
    • Support intercity and interregional connectivity.
    • Enhance access to national infrastructure.
    • Facilitate the movement of goods and people across the region.

• National Tertiary Roads

  • Encompass local roads under the Department of Public Works and Highways (DPWH).
  • Functions:
    • Connect rural communities and villages.
    • Support local transportation needs.
    • Facilitate access to community services.

• Barangay Roads

  • Refer to local roads within barangays, providing essential connectivity within communities.
  • Functions:
    • Connect barangays to municipal and city centers.
    • Provide access to rural communities.
    • Support local transportation needs.
    • Facilitate access to community services.

• State Highway

  • Connect the capital city of a state with its district headquarters, major towns, and other highways.
  • Functions:
    • Basic road to access from one property to another.

• Country Road

  • Usually unpaved rural road off the main highway.
  • Functions:
    • Offer better transportation facilities.

• Local Road

  • Dedicated to public use for traveling.
  • Functions:
    • Provide a high level of safety and access to neighborhood services and facilities.

Surveys of Different Types of Roads in the Philippines

• Road Network Surveys:

  • Assess and manage the road infrastructure.
    • Provide valuable insights into the structure, connectivity, and functionality of the road network.

• Economic and Social Impact Survey:

  • Assess the broader effects of road infrastructure on communities and economies.
  • Crucial for understanding how road projects influence local development, property values, social interactions, and overall quality of life.

• Infrastructure Quality Survey:

  • Evaluate the condition and performance of infrastructure assets, including roads, bridges, tunnels, and other structures.
  • Essential for ensuring that infrastructure meets safety standards, performs effectively, and requires appropriate maintenance or upgrades.

• Road Condition Survey:

  • Maintain and improve the quality of road infrastructure.

Design Speed

• The target speed at which drivers are intended to travel on a street, and not the maximum operating speed.
• According to AASHO, design speed is "the maximum safe speed that can be maintained over a specified section of highway when conditions are so favorable that the design features of the highway govern.”
• Factors affecting design speed:
  • Type of road.
  • Topography of the road.
  • Type of intensity of traffic.
• General design speed is chosen by administrative decision.

Road Shoulder

• Portion of the roadway between the edge of the traffic lane and the edge of the ditch, gutters, curb, or side slope.
• AASHTO requires its usable pavement width to be strong enough to support a vehicle.
• Importance of Road Shoulders:
  • Serves as a place for vehicles to stop when disabled or for other purposes.
  • Provides a continuous area along the full length of the roadway.
  • Adds structural strength to the road pavement.

Highway Median

• Separates lanes of traffic moving in opposite directions.

• Can be depressed, raised, or flush with the road surface.

• Required on:

  • Freeways.
  • Any street or highway, rural or urban, with 4 or more travel lanes and a design speed of 40 mph or higher.

• The type and extent of median separation depend on:

  • Design speed.
  • Traffic volume.
  • Adjacent land use.
  • Frequency of access.

Type of Road Median

• Transversable Medians:
  • Designed to allow vehicles to easily enter or cross over it.
  • Examples:
    • Raised Median.
    • Flushed Median.
    • Depressed Median.
• Median Openings:
  • No median opening.
  • Median crossover without a left turn bay.
  • Median crossover with a left turn bay.
  • Directional median opening crossover.
  • Two-way left turn lane.

Median Width

• General range of median widths is from a minimum of 6 ft to a desirable dimension of 84 ft or more on freeways and rural areas.

• Urban Land Service Highways

  • 32 feet wide to accommodate future widening (12-foot lane, 3-foot shoulder in each direction, 2-foot median concrete barrier curb).
  • 16 feet wide where no future widening is anticipated.

• Rural Land Service Highways

  • 46 feet wide for future 12-foot lane and 5-foot shoulder in each direction with a 12-foot grass median.