Have you ever analyzed an intersection or interchange and wondered what alternative geometric design may offer the best solution? Well, wonder no more. There are several tools available to help determine the “best value” for any given intersection—in conjunction with preliminary design and analysis.
As engineers, it is our job to provide the best design possible. This also applies to analyzing alternative intersection and interchanges options. Alternative intersection/interchanges can provide improved safety and performance over conventional designs, sometimes at a lower construction cost. Currently, nine states have policies in place to review alternative designs. Another six DOTs are working on developing alternative design policies. This is less than 30% of the DOTs, but the majority of the DOTs have champions for various types of alternative intersections.
The evaluation of alternative designs should be conducted in two stages. Stage 1 should be a high-level assessment that considers all possibilities but quickly filters down to a short list. Stage 2 is a more rigorous assessment of the selected performance criteria. If you are evaluating an intersection or interchange in a state that doesn’t have a policy, here are some tools to help you navigate this process:
- ICE-Intersection Control Evaluation, used in California, Florida, Georgia, Indiana, Minnesota, Nevada, Pennsylvania, Washington State and Wisconsin, is the most common tool used to date. This tool aids in the determination of a preferred alternative for a given intersection project by providing an objective, quantifiable basis to compare the safety performance of different intersection types in terms of predicted crash frequency and severity.
- Capacity Analysis for Planning of Junctions (Cap-X) Tool-FHWA is a tool that can be used to evaluate selected types of innovative junction designs using peak flow volumes. It uses the method of critical lane volume summation to provide planning capacity assessment to be used prior to conducting a more demanding traffic simulation.
The tools listed above help the designer with the quantitative (traffic operations & safety performance) aspects of each alternative. But there are qualitative considerations that should also be equally evaluated, including project purpose and need, multimodal needs, land use, community goals, constructability, environment, right-of-way, and cost-effectiveness. Alternative Intersections/Interchanges: Information Report (AIIR) Chapter 10 Alternative Intersection Assessment Methodology Alternative Intersection provides a qualitative assessment of alternatives as a function of pedestrian mobility, right-of-way availability, and access assessment.
Developing a table that compares and ranks the alternatives for each of these categories will help document the evaluation process and determine which alternative moves onto Stage 2. Lastly, engineering judgement should always be used to determine which intersection types may be most appropriate based on site conditions and the purpose and need.
As experienced traffic engineers, our team can help explore the different alternatives to suit the specific needs of our clients. Understanding the effectiveness of each alternative design aids in the final decision. Stay tuned for a blog exploring more about these alternatives in the near future.
