13.2.3 Design Objectives

The goal of any intersection design, regardless of type or location, should be to implement the following principles:
  • Reduce vehicle speeds through the intersection as appropriate;
  • Provide the appropriate number of lanes and lane assignment to achieve adequate capacity, lane volume and lane continuity;
  • Provide channelization and appropriate signage that operates smoothly, is intuitive to drivers, and results in vehicles naturally using the intended lanes;
  • Provide suitable intersection radii so all turning movements are acceptable for the design vehicle;
  • Meet the needs of pedestrians and bicyclists; and
  • Provide appropriate sight distance and visibility.
Each element described above influences the operational efficiency and potential for crashes at intersections. When developing an intersection design, the appropriate balance of operational performance for various modes, safety, and cost considerations should be sought throughout the design process. Favoring one component of the design may negatively affect another.
The design of each intersection should achieve an appropriate balance among the competing needs of pedestrians, bicyclists, motor vehicles, and transit with respect to safety, operation efficiency, convenience, ease, and comfort.
Four basic elements should be considered in intersection design:
  1. Human Factors
    • Driving habits;
    • Ability for users to make decisions;
    • User expectancy;
    • Decision and reaction time; and
    • Pedestrian and bicyclist behavior.
  2. Traffic Considerations
    • Functional Classification of each intersecting roadway;
    • Existing and expected future crash frequency and severity;
    • Design and actual capacities for all modes of traffic;
    • Design-hour turning movements;
    • Size and operating characteristics of vehicles and modes;
    • Potential conflicts between transportation modes;
    • Vehicle Speeds;
    • Transit usage and stop locations; and
    • Railroad crossing accommodation, if applicable.
  3. Physical Elements
    • Character and use of abutting property;
    • Available right of way (ROW);
    • Pedestrian and bicyclist facilities;
    • Transit facilities, if applicable;
    • Vertical and horizontal alignments at the intersection (see
      Section 4.8.5
      );
    • Sight distance;
    • Angle of the intersection;
    • Speed change lanes;
    • Traffic control devices;
    • Lighting;
    • Roadside design features;
    • Crosswalks;
    • Adjacent driveways and driveway spacing;
    • Drainage considerations; and
    • Provision for utilities.
  4. Economic Factors
    • Cost of improvements and expected benefits; and
    • Cost and effectiveness of controlling access points to abutting residential or commercial properties.
Refer to
AASHTO’s A Policy on Geometric Design of Highways and Streets
for additional design objectives and considerations.