The pedestrian trail being built along University Drive-Highway 1804 includes a bridge that is different from the usual structures the North Dakota Department of Transportation has constructed for this purpose.

The 134-foot, $205,714 structure is a locally manufactured, prefabricated, prestressed concrete through truss with a recessed deck, said Scott Olson of Ulteig Engineers.

Its design isn't typically incorporated by the state for the purpose of a pedestrian bridge, but in this case it's considered the most effective and efficient.

Northern Improvement, Strata and Mariner bid on the project, with Northern coming in lowest. The concrete work was subcontracted to Ernie's Concrete, of Minot. The engineer's estimate for the project was $242,575.

The new path will extend some two miles from Burleigh Avenue to the south entrance of the University of Mary, following the west side of University Drive-Highway 1804.

It was suggested that a commercially made steel bridge would have been a cheaper alternative. In fact, one can be found in north Bismarck in the pedestrian path system near the golf course.

Olson said that when the bridge was put out for bid, contractors were given two alternatives: the concrete through truss and the steel bridge. None of the three contractors bidding on the bridge chose the commercial steel version.

NDDOT's Larry Schwartz said there are likely several reasons why the contractors chose the concrete version, adding that it was unlikely all three would bid the same project if they could have built the steel bridge for less.

The beam is fabricated in Menoken, then trucked to the site, where a crane places it on the piers on either side of Apple Creek. The creek bed itself was never disturbed in the construction of this bridge, Olson said.

Usually, when these beams are used for a highway bridge, a deck is poured across the top of the beams. In this case, with only one beam being used, the path is poured on the inside of the beam, and the sides of the beam, which extend up from its base, will be incorporated as part of the railing.

Because of the shape of the beam, it can be placed on the piers and remain well above the water. At the same time, the deck is lower, allowing it to become a part of the path without having to build up the approaches on either side to meet it.

Early in the planning, it was decided not to make the pedestrian bridge part of the highway bridge structure because of safety, and also to allow contractors to leave portions of the highway bridge open as it is being built.

Because both bridges are being built of concrete, contractors can move crews and equipment back and forth between the projects, allowing time for the concrete to set. This also allows for some savings as people and tools are used more efficiently, Olson said.

Olson also said that the closest manufacturer of a steel bridge is in Minnesota, while the concrete bridge materials are all local.

The path is scheduled for completion Nov. 1.

(Reach reporter Gordon Weixel at 250-8255 or gordon.weixel@;bismarcktribune.com.)