An international review on one and two level innovative unconventional intersection and interchange.

The research on road intersection and interchange has recently allowed to design innovative one and two level unconventional layouts (UIIDs) which are of undoubted interest, especially in terms of traffic functionality and safety. The main objective of the paper is to discuss the geometric layouts, the principal advantages and the disadvantages, in terms of cost, safety, performances of the most interesting UIIDs, like two-level signalized intersection (TLSI), single-point urban interchanges (SPUI), center-turn overpass (CTO), echelon interchange (EI), Crossover Diamond interchanges (DCD), Upstream Signalized Crossover Intersection (USC), Median U-turn Intersection (MUT), “Target”, “Flower”, “C” and “Turbo” roundabouts. Although many studies clarify the benefits of unconventional intersection and interchange designs (UIIDs) their implementation around the world is slow, mainly due to poor public support. In any cases, for some layouts the few UIIDs installations so far implemented around the world have not allowed sufficient research in order to analyze the measure of effectiveness (MOE) validated by field observations. Other layouts presented in the paper are prototypes and, for this reason, have been tested only by means of microsimulation, in prefixed traffic scenarios.