Some transportation agencies are using single-point urban interchanges as a strategy to maximize downstream access spacing on crossroad facilities within developed urban areas. This interchange form by its nature increases spacing distances compared with other service and system interchange forms. The interchange form further reduces the number of signalized intersections on a crossroad facility by maintaining a single interchange terminal.
Access Spacing Relationships
Service interchanges (i.e., diamond and single point) typically require less downstream access spacing on crossroads compared with that of cloverleaf and higher-level system interchanges, owing to the fewer required weaving movements and vehicular deceleration needs.
As turning movement complexity increases and traffic controls are introduced at a downstream intersection the more access spacing distance is required on the crossroad facility. The type of downstream intersection also coincides with the downstream storage length requirements, cycle length, and volume factors used to select appropriate access locations.
Design speed plays an important role in selecting the appropriate spacing distance on a crossroad facility; that is, the higher the speed, the longer the access spacing distance should be. The general physical relationships between design speed and the braking distance needed to bring a vehicle to a stop are understood. However, the additive implications associated with performing multiple functions and then relating them to the distance necessary between
access points is still being debated.
consistently throughout North America.
Deployment Results on Interchange Projects
It was found that more than three-quarters of the surveyed transportation agencies acquire access rights on crossroads in the vicinity of interchanges.
Twenty-six of the 33 responding agencies reported that 60% or more of their access management techniques in the vicinity of interchanges are deployed on new interchange projects, whereas only 14 of 29 stated that those techniques were deployed during retrofit interchange projects.
The majority of responding agencies indicated that they relocated, consolidated, or closed existing access driveways, median openings, frontage roads, or public street connections as part of their new or retrofit interchange project.
Some responding states found funding to be critical to the success of the new and retrofit interchange projects. Funding primarily affected the ability to purchase right-of-way.
The level of success for nearly all projects was based on the fundamental strength of the transportation agencies' legislative rules or regulations, along with the ability of the agencies to conduct successful and meaningful public involvement programs as part of the projects.