The decision to not choose a Single Point Urban Interchange (SPUI) for this location was carefully considered throughout MDOT's study. While the SPUI was initially a strong candidate, several factors led to its exclusion.
In terms of traffic efficiency, the SPUI and the Diverging Diamond Interchange (DDI) were closely matched, with little discernible advantage or disadvantage for either. However, the SPUI introduced an additional signal phase compared to the DDI, impacting signal timing flexibility along the corridor.
Despite apparent community support for the SPUI, three significant drawbacks influenced the decision against it. First, there were conflicting needs for left-turn storage for Dickerson Road and the northbound I-75 Ramp. Additionally, the dependency on visible pavement markings in snowy regions posed a challenge. Last, the absence of options to place a center pier for the I-75 bridges resulted in very long bridge span lengths, affecting bridge costs.
While SPUIs perform well under heavy traffic loads, they can create perceived excessive wait times during off-peak traffic. Moreover, the expansive section of pavement required by SPUIs, coupled with limitations in aesthetic appeal, contributed to the decision.
In summary, the choice against a SPUI considered a comprehensive evaluation of traffic efficiency, community input, conflicting needs, environmental considerations, and aesthetic concerns.