Work to repair a stretch of the M5 in the West Midlands is running six months behind schedule, the BBC has been told.
Repairs and waterproofing to Oldbury Viaduct between junctions 1 and 2 have been under way since April 2017, reducing the number of lanes.
A higher number of repairs than anticipated and hot weather are among the reasons for the delays.
A spokesperson for Highways England said they were "committed to completing the work as quickly as possible".
The government body said it hoped to have the work completed as soon as possible in 2019.
"The work we are doing to repair the M5 Oldbury Viaduct is absolutely essential if drivers are to continue using it for years to come," a Highways England spokesperson added.
"We're committed to completing the work as quickly and as safely as possible and we're doing all we can to reduce disruption to motorists, businesses and residents."
The extreme winter and recent hot weather has meant workers could not lay the waterproofing material as it can only be applied in temperatures less than 30C (86F).