When does the Tremaine Road–Highway 401 interchange open? Halton's last stated target is December 2026

The short answer

Halton Region's only published timing for the new Tremaine Road interchange with Highway 401 is in its Tremaine Road Improvements Project update, which says the interchange connection is "currently expected to open in December 2026". That page was last updated on July 8, 2025. As of October 11, 2026, Halton has not published a newer date, a revised target or a confirmed opening day.

The most recent Halton mention is an August 21, 2026 article on the opening of the William Halton Parkway extension, which tells readers to stay tuned for updates on other major road projects, including the Tremaine Road/Highway 401 Interchange. It gives no date. Halton's road and construction project index, checked on October 11, 2026, does not list a Tremaine Road project page.

What the project includes

Halton describes the work as the final phase of a major upgrade that includes a new four-lane bridge, a realigned road for better north-south connectivity, and a future interchange giving direct access to Highway 401. It says the new route improves traffic flow and safety between Steeles Avenue and Campbellville Road, and that the interchange will provide direct access to and from Highway 401, reduce travel times for commuters and commercial vehicles, and improve emergency response access.

Halton says the new bridge opened with two lanes and will eventually be four lanes when the project is complete. Once the new road opened, the old two-lane bridge over Highway 401 was permanently closed starting July 7, 2025, and Highway 401 was closed overnight between Regional Road 25 and Guelph Line from 9 p.m. on July 12 to 9 a.m. on July 13, 2025, to demolish it. Halton says it is working with the Ministry of Transportation on the project.

Ontario's Environmental Registry records that on September 13, 2020, the Minister issued an Endangered Species Act permit to Halton Region for widening and realigning Tremaine Road and the associated Highway 401 interchange in Milton, because the work affects the habitat of Redside Dace in a tributary of Sixteen Mile Creek.

Where to check for an update

• Halton Region: halton.ca/construction, where residents can sign up for construction notices, or call 311.
• Highway 401 lane and ramp closures: the Ministry of Transportation's Ontario 511 service.
• This page will be updated when Halton publishes an opening date.