The 10 Principles of Access Management
1. Provide a specialized roadway system
Different types of roadways serve different functions. It is important to design and manage roadways according to the primary functions that they are expected to serve.
2. Limit direct access to major roadways
Roadways that serve higher volumes of regional through traffic need more access control to preserve their traffic function. Frequent and direct property access is more compatible with the function of local and collector roadways.
3. Promote intersection hierarchy
An efficient transportation network provides appropriate transitions from one classification of roadway to another. For example, freeways connect to arterials through an interchange that is designed for the transition. Extending this concept to surface roadways results in a series of intersection types that range from the junction of two major arterial roadways, to a residential driveway connecting to a local street.
4. Locate signals to favor through movements
Long, uniform spacing of intersections and signals on major roadways enhances the ability to coordinate signals and ensure continuous movement of traffic at the desired speed. Failure to carefully locate access connections, or median openings that later become signalized, can cause substantial increases in arterial travel times. In addition, poor signal placement may lead to delays that cannot be overcome by computerized signal-timing systems.
5. Preserve the functional area of intersections and interchanges
The functional area of an intersection or interchange is the area that is critical to its function. This is the area where motorists are responding to the intersection or interchange, decelerating, and maneuvering into the appropriate lane to stop or complete a turn. Access connections too close to intersections or interchange ramps can cause serious traffic conflicts that impair the function of the affected facilities.
6. Limit the number of conflict points
Drivers make more mistakes and are more likely to have collisions when they are presented with the complex driving situations created by numerous conflicts. Conversely, simplifying the driving task contributes to improved traffic operations and fewer collisions. A less complex driving environment is accomplished by limiting the number and type of conflicts between vehicles, vehicles and pedestrians, and vehicles and bicyclists. The number of potential conflicts increases substantially when pedestrian and bicycle movements are considered.
7. Separate conflict areas
Drivers need sufficient time to address one potential set of conflicts before facing another. The necessary spacing between conflict areas increases as travel speed increases, to provide drivers adequate perception and reaction time. Separating conflict areas helps to simplify the driving task and contributes to improved traffic operations and safety.
8. Remove turning vehicles from through-traffic lanes
Turning lanes allow drivers to decelerate gradually out of the through lane and wait in a protected area for an opportunity to complete a turn, thereby reducing the severity and duration of conflict between turning vehicles and through traffic. They also improve the safety and efficiency of roadway intersections.
9. Use nontraversable medians to manage left-turn movements
Medians channel turning movements on major roadways to designated locations. The majority of access-related crashes involve left turns. Therefore, nontraversable medians and other techniques that minimize left turns or reduce the driver workload can be especially effective in improving roadway safety. Full median openings, which allow left turns from either direction, are best provided at signalized intersections and unsignalized junctions of arterial and collector streets. Full median openings in other unsignalized locations can adversely affect safety and traffic flow, but may be appropriate in some areas where analysis indicates that traffic operations and safety would be improved.
10. Provide a supporting street and circulation system
Well-planned communities provide a supporting network of local and mobility. Connectivity can be maintained while advancing access management objectives for arterial roadways by ensuring that local street connections to the arterial conform to the adopted connection spacing interval.
SOURCE: TRB Committee on Access Management (2003). Access Management Manual. Transportation Research Board of the National Academies of Sciences. http://www.accessmanagement.info/manual.html