Wallace, Idaho, sits on the floor of a narrow canyon in the Silver Valley. Its downtown is two or three blocks of brick and clapboard buildings from the late 1800s, standing tightly together along a handful of streets. Above the rooflines runs Interstate 90, carried on a concrete viaduct. The highway does not pass through Wallace; it passes over it. The arrangement was the result of a long legal fight, and the viaduct opened in 1991 as the final completed section of the coast-to-coast interstate.
Silver valley
The South Fork of the Coeur d'Alene River cuts through the mountains just west of the Bitterroot Range. The valley floor is narrow, and the flat ground is crowded with the river, a railroad, and a two-lane road. Silver, lead, and zinc were discovered in the surrounding hills in the 1880s, and for the next century the Silver Valley was one of the most productive mining districts in the United States. Wallace, at about 2,700 feet in elevation, was the commercial hub for mines up and down the canyon. The town had a depot, hotels, banks, saloons, and offices, all built in the brick masonry of its era. Many of the buildings went up between 1890 and 1910 and have remained in their original form since. The town's compact street grid occupies the same narrow shelf that the railroad and the river use.
The freeway fight
Interstate 90 was routed through northern Idaho along U.S. 10, which ran through the center of Wallace. In the 1960s and 1970s, the Idaho Department of Highways proposed upgrading the road to interstate standards by widening it at grade. In a tight town like Wallace, that meant removing a large share of the historic commercial buildings to create room for four lanes, turning the main street into a sliver separated by concrete. Residents organized, and the National Register of Historic Places was asked to review the entire townsite. The listing was granted, covering the buildings, the streets, and the layout of the town. Federal law required state and federal agencies to evaluate the effect of the proposed highway on listed properties. The highway department considered relocating the interstate to the slope above the town, but the soils were unstable and the cuts would have been enormous. A tunnel was rejected on cost. The final alternative was an elevated structure that could run above the old railroad corridor, outside the building footprints.
An interstate on stilts
The viaduct was built over the railroad right-of-way on the edge of the downtown. Its concrete piers are spaced to clear the cross streets, and its deck carries four lanes at about the level of the town's second-story windows. From the sidewalks, the underside of the interstate is a long concrete lid, continuous except where the cross streets pass underneath. It blocks part of the sky and changes the light on the street below. Truck traffic rumbles over the expansion joints, and the sound reflects off the brick walls. In 1991, the final section of I-90 in the United States opened here, closing the last gap in the 3,000-mile route between Seattle and Boston. For years before that, drivers had to exit the interstate at one end of town, follow the old highway through Wallace's stoplights, and re-enter the freeway at the other end. With the viaduct, the through traffic no longer touched the ground.
Living under the highway
Wallace today is home to about 800 people. The old commercial blocks remain occupied by a bookstore, gear shops, restaurants, and a museum in a former brothel. A sidewalk plaque near the center of town calls Wallace the “Center of the Universe.” The town leans on its mining history and its proximity to the Route of the Hiawatha, a rail-trail east of town that passes through old tunnels and across trestles. The interstate above does not dominate the town the way a viaduct might in a large city; it is set far enough back that the main street is open to the sun. But it is always present, a permanent second structure over the first one. Wallace did not get its road by way of demolition. It got a road that had to be built over the top of the town.
