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Zimmerman Trail Tunnel

City of Billings, Montana

The Zimmerman Trail Tunnel cross-section features one 14 foot (4.3 meter) lane with an 8 foot (2.4 meter) shoulder for each direction of traffic. The highway tunnel also allows for a 16 foot (4.9 meter) vertical clearance, an additional 2 feet (0.6 meters) for roadway signage, and 5 foot (1.5 meter) diameter jet fans.

Tunnel Engineering Feasibility Study:

Gall Zeidler Consultants developed the tunnel engineering aspects of the feasibility study for the Zimmerman Trail alternatives analysis. The scope of services included input to the alignment studies, review of the geotechnical program, interpretation of the geotechnical data, developing typical cross-sections along with  excavation and support measures, and recommendations for waterproofing, final tunnel lining and tunnel ventilation.

The initial rock support was separated into three categories: Portal Rock Support, Ground Class I Rock Support, and Ground Class II Rock Support. The final lining is cast-in-place concrete with reinforcement as required, reinforcement provided typically in portal area only.


Billings, Montana


2010 – 2011


Highway Tunnel


Approximately 2,020 – 3,700 feet (615 – 1,126 meters) Depending on Alignment Options Selected


Height: 34.4 feet (10.5 meters)
Width: 61 Feet (19 meters)


Eagle Sandstone Formation (Very-Fine to Fine-Grained, Cross-Bedded Sandstones and Shales) and Telegraph Creek Formation (Shale and Sandy Shale)


HDR, Inc.


City of Billings, Montana