Allowing a greater percentage of traffic to move a greater percentage of the time means fewer lanes are needed to move the same amount of traffic with non-traditional intersections than with traditional designs. By reducing the need for additional lanes, less right-of- way is needed to construct the interchange. As a result, the construction costs of non-traditional designs is substantially less than their traditional counterparts.
Better Design Means Safer Roads
In addition to increasing capacity and reducing costs, all non-traditional intersections are thought to be substantially safer than traditional designs, due to the reduction of the number of conflict points. Conflict points have always served as a surrogate for safety (with the least number of conflict points being the safest). Traditional intersection forms typically have 32 conflict points, while most non-traditional forms have 16. Likewise, a traditional diamond interchange has 30 conflict points, while most non-traditional interchange forms have only 16.
Fewer Stops Cause Less Pollution
Many areas of the country are in non-attainment for air quality. As a result of having two signal phases, the efficiency of non-traditional designs permits more vehicles to be moving within a specified time period than the traditional multi-phased designs which operate with more delay and idling while waiting on their signal phase to turn green. Based on VisSim models, air pollution can be reduced by 25%-30%, depending on the pollutant, with non-traditional designs when compared to the same traffic volume with traditional designs.
Typically, non-traditional designs provide a win/win/win/win over their traditional counterparts by providing:
- Higher capacities lane for lane
- Safer designs with less conflict points
- Reductions in air pollutants
- Less expensive designs
WSP in Action
WSP is proud to deliver these benefits to our clients. In North Carolina (US), implementation of superstreets meant travel time improvements by 20%, reduction in collisions by 56%, and fewer injuries and fatalities by 63%. In the case of the A19/A1058 Coast Road Junction Improvement (UK), our primary objective was to relieve congestion by realigning the A19 to pass beneath the existing grade separated junction. A significant reduction of 25% in capital works cost has been achieved through a rigorous approach to value engineering and focused risk management.
