The latest road closure necessitated by construction of the Ion light rail transit system will be a lengthy one.

Both off-ramps from the Conestoga Parkway to Northfield Drive are expected to close Monday.

They won’t reopen for 18 months.

Construction planners don’t expect the on-ramps to be affected.

Temporary, intermittent lane closures will also occur on Northfield between King Street North and the CN Rail tracks, as well as some nighttime lane closures on the highway.