ROAD CAPACITY

• ROAD CAPACITY as defined in the U.S highway capacity manual (HCM), is the maximum number of vehicles that have a reasonable expectation of passing over a given section of a lane or a roadway in one direction or both directions during one hour under prevailing and traffic conditions.
• ROAD TYPES:

  • LOCAL ROAD
  • FREE WAY
  • COLLECTOR
  • ARTERIAL
• FACTORS AFFECTING ROUTE CAPACITY:

  the number of lanes in a segment of the highway is determined by the estimated traffic volume for the design year (AADT) and highway lane capacity at the expected level of service. AASHTO policies accept a dually divided 16 lanes road way with four lanes in each direction on the outside. There are some instances where a reversible lane is located at the center of freeways with unbalanced heavy traffic flow.
• FACTORS AFFECTING ROUTE CAPACITY:

  Lanes and Shoulder Width - it has a significant impact on road capacity. Wider lanes enable vehicles to move freely and safely at higher speeds, allowing more cars to travel simultaneously, thus increasing the overall capacity. And, wide shoulders provide space for vehicles to pull over during emergencies or breakdowns without disrupting the flow of traffic.
• FACTORS AFFECTING ROUTE CAPACITY:

  Terrain and Road Gradient - Flat surface allows for smoother traffic and higher capacity, while hilly or mountainous terrain requires sharper curves and narrower lanes, reducing capacity. Complex engineering like tunnels or bridges may also limit traffic flow. Road gradient (the slope of the road) affects capacity by slowing vehicles, especially heavy trucks, on steeper inclines. This leads to congestion and reduced speed limits, further decreasing road capacity.
• FACTORS AFFECTING ROUTE CAPACITY:

  Traffic Composition - refers to the types and proportions of vehicles using a roadway, which significantly affects route capacity. A mix of vehicle types, such as cars, trucks, buses, and motorcycles, influences traffic flow and overall efficiency.
• FACTORS AFFECTING ROUTE CAPACITY:

  Side Friction - refers to external factors along a roadway that disrupt traffic flow, such as road furniture (signs, barriers) and the presence of pedestrians. These elements significantly reduce route capacity by causing distractions, interruptions, and reducing available space for vehicles.
• LEVEL OF SERVICE - Given a fixed volume of traffic flow and vehicle composition, the geometric design of highways, such as the horizontal and vertical curves, grades, lane width, number of lanes, etc. affects the travel speed of vehicles sand the interaction between vehicles. The out come of such an effect is the observable operational performance of the highway qualitatively represented by the highway level of service.
• AASHTO stands for the American Association of State Highway and Transportation Officials. It's an organization that publishes guidelines, standards, and best practices for transportation design, construction, and maintenance in the United States
• AADT stands for Average Annual Daily Traffic. It represents the total volume of vehicle traffic on a road segment divided by the number of days in a year.