The cloverleaf style of interchange has been around for over 60 years. There are hundreds in use throughout the United States. This design was originally used at the junctions of two freeways or a freeway and major arterial. However in recent years many of these cloverleaf interchanges have reached a point where they have traffic volumes far beyond what their original designers envisioned. At many freeway-to-freeway junctions, the cloverleaf interchanges have already been replaced by directional interchanges and most agencies would like to replace more in the future. But funding realities make it difficult to keep pace with needs. As a result, agencies are often required to continue operating cloverleaf interchanges beyond their design life. Over the years there have been some geometric changes of a fine-tuning nature that have added capacity and improved safety at older style cloverleaf interchanges. This paper presents a historic background of the cloverleaf design; traffic conditions that eventually lead to failure and then presents design alternatives to extend the interchange life. The paper will conclude with results from examples of successful cloverleaf enhancement projects in Minnesota and the results from traffic simulation, which was used to evaluate the measures that could be used to improve cloverleaf operation.
Abstract