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Excavation of the rock in order to create the tunnel The tunnel section once it had been completed

Designing Alaska's innovative Whittier Tunnel

The longest highway tunnel in North America, the Whittier tunnel is also the first tunnel with a unique traffic-control system that regulates rail and vehicular traffic.

2001Schreyer Award for Civil Engineering (Canada's highest award for engineering excellence), Canadian Consulting Engineers
2001Grand Award, American Consulting Engineers Council
2001Award of Merit, ASCE
2001Best Project (public sector over $15 million), Design/Build Institute of America
2001Outstanding Engineering Award, FW Dodge
2000National Winner - Global Award, American Road & Transportation Builders Association
2000Project (public sector over $15 million), Portland Cement Association


In 2000, a single-track, hard-rock rail tunnel connecting the port of Whittier, Alaska, to the Seward Highway was converted to dual rail/highway use. Two and a half miles (four kilometers) long, the converted tunnel is still the longest road tunnel in North America.


As lead designer for this design-build project, Mott MacDonald achieved several firsts. The Whittier Tunnel was the first to combine rail and highway use in North America, the first to combine jet and portal fans in its ventilation system, and the first to use a unique traffic control system that ensures no conflict between rail and highway service along the same alignment.

After 15 years of uninterrupted service, Mott MacDonald was retained a second time to help meet maintenance and rehabilitation needs. We conducted assessments, made recommendations, provided cost estimates, and completed design and bid-ready construction documents for the upgrade of the groundwater collection and conveyance systems.


The converted tunnel is the longest road tunnel in North America. Its dual function is accomplished with a precast concrete roadway surface with integral rails and a sophisticated traffic control system that allows both control of the single-lane highway traffic flow direction as well as the safe operation of train traffic.

The tunnel was designed for temperatures as low as –40°F and winds up to 150 mph, and portal buildings were built to withstand avalanches.

This landmark project boasts several “firsts,” including these:

  • Longest highway tunnel in North America.
  • First combined-use rail-highway use tunnel in North America.
  • First tunnel to use a ventilation system that combines jet and portal fans in US.
  • First tunnel with a unique traffic-control system that regulates rail and vehicular traffic.
  • First tunnel designed to operate in temperatures down to –40°F and winds up to 150 mph, and with portal buildings able to withstand avalanches.
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