At four-phase conventional intersections where traffic demand is near or above capacity, alternative intersections may perform better. Alternative designs with two-phase traffic signals such as reduced conflict intersections (RCI, also called RCUT, J-turn, and superstreet) result in shorter travel times, fewer crashes, and better pedestrian service in North Carolina (NC). However, retrofits to designs with two-phase signals may be negatively impactful and unpopular. Higher minor street demand, lack of precedent, and complaints (from neighbors, business owners, politicians, media, etc.) are among the possible obstacles for constructing two-phase intersection designs in many locations. Intersections with three-phase signals might provide some of the two-phase design advantages while also providing more direct movements and alleviating some public concerns.
This study assists Departments of Transportation (DOTs) in addressing questions such as: (1) At what locations are three-phase designs most well suited? (2) How much do they cost, especially compared with other intersections like RCIs? (3) What are the considerations needed for pedestrian and bicyclist safety? (4) What kind of geometric and right-of-way (ROW) limitations are faced during construction? (5) What designs would be most readily accepted by the public?
In this project, the research team completed a state-of-the-art literature review, conducted microsimulation analysis to evaluate operational performance, assessed the safety of three-phase designs using various methods and developing new tools, conducted a cost/benefit analysis, and developed a public acceptance scoring system (PASS). Overall, three-phase intersection designs were found to have significant potential benefits across all measures of effectiveness (MOEs). The traffic operations analysis revealed that six three-phase alternative intersections—offset thru-cut, thru-cut, reverse RCI, partial CFI, CFI/MUT combo, and MUT Redirect Major (MUT #1)—may perform as well as or even better than two-phase designs under certain traffic conditions, such as those with high-turning traffic volumes. The CFI/MUT design outperformed the partial CFI in four MOEs and matched it in traffic operations. As a result, the CFI/MUT could be a promising alternative where there are concerns, such as pedestrian safety or ROW limitations, about implementing a partial CFI.
