A complex interchange contains many lanes and carries high traffic volumes through a maze of tightly spaced ramps and connectors. Drivers often have to make multiple lane changes, requiring intense attention and rapid decision making. As the Federal Highway Administration and State departments of transportation (DOTs) plan improvements to complex interchanges, they face the challenges of making those facilities more efficient and easier to use while meeting higher traffic demands, adopting modern engineering standards, and improving safety. This paper offers guidance and tips gleaned from the literature and from field experience that could help highway designers deal with challenges in designing complex interchanges. One of the primary design issues is that complex interchanges usually do not have conventional layouts. Instead, each complex interchange is unique, customized by State DOTs to meet the specific transportation needs of that location and region. Adding to the challenge is the uncertainty regarding how motorists will comprehend the completed design and whether they will be able to perform the driving manoeuvres safely and appropriately. Four key issues for interchange designers' attention are ramp spacing, guide signing, route continuity, and lane balance. These issues, either individually or combined, can affect the project's design, traffic flow, safety, and cost. The use of design visualization, which uses techniques such as computer graphics, driving simulators, and animation to provide a representation of proposed alternatives and their associated impacts, could improve complex interchange projects. The use of road safety audits also could improve complex interchanges. When designing complex interchanges, taking the entire corridor into consideration, not just the interchange itself, can improve the overall safety and efficiency of the regional transportation system. The Marquette Interchange, which links three interstates in downtown Milwaukee, is highlighted as an example of a successful rebuilding of a complex interchange. (Author/publisher)
Abstract