Development of criteria for altering existing full cloverleaf interchanges to improve the traffic operations and safety of this particular configuration. Only the standard cloverleaf configuration with a loop ramp and an outer connection in each quadrant was considered in this study. The data based form the Interstate System Accident Research-Study II project was used to describe the spatial distribution of accidents within the interchange and its relationship to increasing traffic volume. Highway Capacity Manual procedures were used to describe the capacity characteristics of the various junction points within the standard cloverleaf. The results of these two analyses were combined to describe the range of traffic situations that could cause a breakdown in operations on any standard cloverleaf. A survey of ten major states having experience operating full cloverleaf interchanges led to the identification of two problem situations that are the most likely to lead to operational breakdowns on a standard cloverleaf interchange. The first problem situation identified dealt with the operation of the weaving section as it approached capacity. The second situation dealt with the operation of the free-flow ramp terminals onto a multi-lane, non-access-controlled crossroad with strip development in close proximity to the terminals. Solutions that retained, modified or eliminated the standard cloverleaf flow pattern were examined. The results indicated that solutions involving the redesign and reconstruction of the interchange (modify or eliminate rather than retain) provide the only acceptable level of effectiveness. /FHWA/.
Abstract