• Hatcher Technical, Inc.

    Sarah Mildred Long Bridge Replacement

    Kittery, Maine to Portsmouth, New Hampshire, United States

Project Summary


The approximately USD 158.5 million Sarah Mildred Long Bridge Replacement project is a partnership between the Maine and New Hampshire Departments of Transportation, with Maine DOT taking the lead. The bridge will provide another link between the two states, providing redundancy for the nearby Interstate 95 Bridge. The project team wanted to identify in the shop drawing phase all possible constructability issues that would hinder field operations. By anticipating and resolving problems early on, the entire project team hoped to eliminate costly delays in the field.


During the shop drawing process, Hatcher Technical created fully integrated 3D models to replicate the most intricate areas of the structure – the main tower caps, the railroad bridge precast end and pier segments, and the vehicle bridge precast end and pier segments. Using MicroStation to generate the fully integrated 3D models saved the project from likely schedule delays and additional costs. The 3D models also facilitated the production of clean shop drawings that sped through approval for construction upon their first submittal, saving time and rework. The models resulted in a realistic view of the segments to be constructed, allowing both the management and site teams to understand the complexities of fabrication to develop strategies to maximize efficiency and constructability.


The bridge has complex structural components that are tightly packed with post-tensioning hardware, reinforcing steel and other items integral to the design. The replacement bridge is 56’ higher than the current bridge, allowing more ship traffic to pass underneath, without opening the bridge. Furthermore, its hybrid span will also lower to railroad level for crossing trains. The bridge will have 11 fewer piers in the river, as well as an improved collision system in case of a shipwreck. The bridge deck will also have wider shoulders for bicycles.


MicroStation was used to create realistic 3D models, integrating all required construction, including post-tensioning hardware, reinforcing steel, various utilities, lift span machinery, ladders, stairs, and platforms. These models highlighted areas of high congestion or conflicting components, and were also critical in finalizing construction sequencing and identifying previously unrealized constructability issues. The center-line of each reinforcing bar is detailed as a "complex chain," and the reinforcing bar is then generated using the "solid by extrusion along" feature using the maximum bar diameter. This process created the reinforcement in the segment, which is then located as necessary to meet the design needs while maintaining conflict-free constructability. Once completed, MicroStation models were exported to 3D PDFs for easy manipulation during project meetings on the construction site. The models are used by project partners to understand how the components fit together, and have been used to sequence construction tasks during the fabrication of the segments.

Project Playbook: MicroStation
  • The team used MicroStation to create realistic 3D models which were critical in finalizing construction sequencing and identifying constructability issues.
  • Other components in the segments, such as threaded embeds and post-tensioning hardware are generated using MicroStation’s wide array of 3D parametric modeling capabilities.
  • The new bridge features an improved collision system in case of a shipwreck and wider shoulders for bicycle traffic.
  • “The robust modeling tools provided in MicroStation makes it possible for Hatcher Technical to develop realistic, complex construction models that allow the project team to build better and smarter with less delays in the field.”

    Jason Hatcher Owner Hatcher Technical, Inc.