MoDOT details $600 million-plus I‑70 rebuild and local interchange work affecting O'Fallon

MoDOT's area engineer, Andy, told the Public Works Advisory Committee on July 16 that the statewide I‑70 program has moved into an aggressive construction phase and that the St. Louis District projects together represent roughly a $600,000,000 investment that will remake segments of I‑70 and related I‑64 links.

Andy said the state-led program aims to provide three 12‑foot lanes in each direction in many places, expanded shoulders, and major interchange work that blends previously separate projects into a single design‑build delivery. "Everything you see on the screen... plays well together," he said, calling the package "the largest project in MoDOT history." He also described pavement work that includes a 9–12 inch pavement section with a chemically treated subgrade intended to improve longevity and reduce water damage beneath the road.

Why it matters: The corridor work will change traffic patterns, add capacity through the Wentzville area and create long-term maintenance advantages by rebuilding subgrade and replacing aging bridge structures. Andy said segments of I‑64 tied to the program may open ahead of the project's full completion; he cited a targeted overall finish in 2028 and specific local milestones (an I‑64 stretch "by the end of the year" and a Forest L interchange by the end of 2027).

Details and designs: Andy described a blended design that postpones smaller disjointed construction zones in favor of larger, coordinated work. He outlined plans for diverging-diamond/roundabout elements at some interchanges and said bridge replacements (including a much longer replacement of the railroad bridge) would be staged using a temporary "shoe-fly" structure to keep rail traffic moving during construction. "We'll build them a temporary structure off to the side and then move their track over to the new temporary bridge," he said.

Local impacts and schedule: The presentation highlighted that MoDOT and Saint Charles County had forward‑funded preliminary studies so design work could proceed when state funding became available. Traffic will be maintained to two lanes in each direction at peak times where possible; some ramp and merge areas will be rebuilt to spread merging distances from a few hundred feet to several thousand. Andy said contractors will diamond-ground new concrete to reduce noise and that designers prioritized longer-lasting pavements and simpler bridge types to ease future maintenance.

Next steps: Andy said he would share a contractor-produced fly-through video with city staff and that more detailed public information, updated schedules and design packages will be released as the design-build contractor advances work.

The committee then asked technical questions about tie-ins (for example whether Route 364 would be extended to I‑70, which Andy said is not planned), roundabout locations, and details of the phased work; Andy answered during a Q&A session.