County seeks temporary reroute on Old Highway 100 as geotechnical work shows major stabilization needed

County engineering staff reported Aug. 25 that geotechnical exploration at the Old Highway 100 closure in front of the former SECO plant indicates the existing alignment cannot be stabilized in its current footprint and that a reroute is planned to reopen the road as soon as possible. The county said it is working to reroute and pave the replacement alignment and aims to open the new alignment before September. Officials said MoDOT will inspect the proposed alignment because the county’s new connection will join the approach to a bridge that MoDOT plans to replace in fiscal year 2027. The county noted a 3-to-4-foot-deep steel natural gas line in the hillside at the site; the gas company granted permission to pave over the line, and staff said the company indicated no safety concern with paving above that line. County staff said they will meet engineers and MoDOT staff “to verify all of the coordination of utilities.”

Staff described plans to pave the new alignment about 30 feet north of the existing road and to match the new road into the approach roughly 450 feet before the bridge, which could allow MoDOT flexibility in final bridge alignment. After the new alignment is opened to traffic, staff said crews will remove remaining asphalt and concrete from the failing section behind barricades to prevent material from sliding into the creek, noting that leaving pavement in the stream would violate Department of Natural Resources and U.S. Army Corps of Engineers rules. The county said it will reuse millings from the existing roadway as base material for the new roadway. A county engineer said he was “very confident” (no guarantee) that the planned work will address the slide problem, but emphasized there are no absolute guarantees.

County officials also said the sheriff’s department has assisted by enforcing lower speeds on New Highway 100 near the school district while the temporary work continues. The committee discussed coordination with school bus routes and said only about 20 vehicles last school year used the specific right turn movement that had relied on the old alignment, so the immediate student-transport impact from the temporary reroute is expected to be limited. The committee heard that MoDOT’s bridge replacement is scheduled for fiscal 2027 and that the county wants the temporary work finished in time to coordinate approaches with MoDOT’s bridge design.

The update included scheduling and construction details but no formal vote; staff described the effort as an active, ongoing project and requested continued attention and coordination with MoDOT and utilities.