I-75/M-32 Interchange Rebuilding and Reconfiguration - Gaylord

MDOT and its consultant considered three primary options for the interchange:

• A Diverging Diamond Interchange (DDI)
• A Single-Point Urban Interchange (SPUI)
• A modified and improved design of the current interchange

While initially considered as an option, MDOT ruled out the option of roundabouts for the interchange early on due to the capacity limitations of roundabouts.

In the quest to determine the interchange that will be part of Gaylord’s future, the Diverging Diamond Interchange (DDI) emerged as the frontrunner, backed by a wealth of supporting data:

• Traffic Operational Analysis:
  • Rigorous analysis reveals that the DDI outperforms other options, ensuring optimal traffic flow well into the future as volumes continue to increase.
• Enhanced Safety Features:
  • DDI's unique design reduces conflict points and turning movements, significantly improving safety for all road users.
• Reduced Signal Phases:
  • Efficiency is key — fewer signal phases are required with the DDI, streamlining traffic movements and minimizing delays.
• Pedestrian-Friendly Design:
  • Prioritizing safety, the DDI requires fewer pedestrian crossings, creating a more accessible environment for all roadway users.
• Local Public Support:
  • Your voice matters, and the DDI has garnered strong local public support. It reflects the preferences and needs of Gaylord’s community members.
• Flexibility for Future Changes:
  • The DDI stands out in its adaptability, providing the most flexibility to accommodate changes in future traffic patterns and development, ensuring a forward-looking solution.
• Optimal Left Turn Storage:
  • Addressing the conflicting needs of Dickerson Road and the northbound I-75 on-ramp, the DDI excels in providing the most left-turn storage, optimizing traffic management.
• Snow-Resilient Design:
  • Acknowledging our winter climate, the DDI is less reliant on pavement marking visibility, ensuring continued functionality even in snowy weather.
• Comprehensive User Experience:
  • Striving for inclusivity, the DDI offers a good level of service for all users, including cyclists and pedestrians, fostering a community-centric design.
• Cost-Effective Bridge Placement:
  • A strategic advantage of the DDI is its ability to allow for the placement of center bridge piers for the I-75 bridges above. This not only reduces costs significantly but also simplifies the construction process.

Overall, the DDI not only optimizes traffic operations and safety but also aligns with the community's preferences.

Examples of Diverging Diamond Interchanges in Michigan include:

• I-94/US-127/West Avenue in Jackson
• I-75/14 Mile and I-75/Big Beaver Road in Troy
• I-75/University Drive in Auburn Hills

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.

The modified and improved design of the current interchange initially appeared as a favorable option for MDOT due to its perceived cost savings over alternatives like the Single Point Urban Interchange (SPUI) and Diverging Diamond Interchange (DDI). However, this option faced challenges, particularly concerning the Dickerson Road intersection.

The requirement for Dickerson Road to align directly across from the I-75 southbound off-ramp, creating a 4-legged intersection, posed a significant issue. This additional leg necessitated an extra signal phase at the intersection, leading to complications in traffic flow. As a result, traffic modeling showed increased delays and longer travel times due to traffic demands, especially in the design year (2045). Looking beyond current traffic volumes revealed significant weaknesses in the resiliency of this design.

Despite MDOT's obligation to investigate the design year (2045), the evaluation extended beyond to assess the model’s long-term resiliency. Ultimately, the modified design did not meet the project goals concerning traffic operations, and it became unsustainable. Additionally, when considering both project cost and benefits, the option with the lowest cost turned out to have the lowest overall project value, further influencing the design decision.