Abstract Manager

Although national and local agency standards get larger and more detailed with each new iteration, there are still many gaps when applying those standards to typical projects and even more gaps when designing for an innovative intersection.  This presentation will use two case studies in Fairbanks, Alaska: one diverging diamond interchange and one hybrid innovative intersection, both of which highlight issues that emerge when “typical” treatments do not apply and solutions that require a myriad of judgment calls.

Engineering judgment is a concept that we seem to get farther and farther away from as our standards try to become more and more prescriptive.  There is a preconception among many engineers, including some traffic engineers, that traffic signal and signing design are standards-driven, cookie-cutter, dry, uninteresting.  The reality is that every design is different.  Each typical intersection contains hundreds of decisions. Innovative intersections require an even more in-depth understanding of the intent behind the standards and a thoughtful interpretation of those intents to create a safe design that can guide road users through an unfamiliar traffic pattern. 

The Steese Expressway-Johansen Expressway intersection located in Fairbanks, Alaska, will be replaced with a diverging diamond interchange (DDI). The area has experienced a significant increase in commercial and residential development and is in of need of mobility and safety improvements. It is the first DDI in the Alaska DOT Northern Region and requires special considerations due to the geometry of the DDI, right-of-way constraints, maintenance concerns, and, of course, weather.

The Gaffney-Airport-Richardson-Steese (GARS) intersection will be a one-of-a-kind, innovative intersection bringing together elements of a continuous flow intersection and median u-turns in a customized, lower-cost solution where an interchange had previously been proposed. This is the first traffic signal encountered traveling into Fairbanks, Alaska, on Richardson Highway. To add to what is already a complex design challenge, the west leg is urban and the east leg serves a US Army Base with limited access.

There is nothing ordinary about these projects, nothing ordinary about the designs, and no computer could apply the engineering judgment needed for these unique solutions.