Work has begun on a year-long programme of roadworks to improve congestion in Swindon.
Extra lanes are being added to Junction 15 of the M4 on the approach to and from the motorway, along with road widening on the nearby A419.
The project is being jointly funded by a group of agencies including Highways England and Swindon Borough Council.
The work is estimated to cost £17.5m and is scheduled to be completed in August 2021.
The council's Gary Sumner said: "This is a notoriously busy bottleneck, the tailbacks at peak time show why this is needed."
Highways England said it hoped the improvements would relieve peak-time congestion and open up housing development in Swindon.
A total of 4,500 homes are currently being considered for construction at nearby Wichelstowe.
Paddy Bradley of Swindon and Wiltshire Local Enterprise Partnership said: "It will help ensure the economic growth of Swindon and the wider region is not hindered by traffic congestion and unreliable journey times."
Residents living nearby will be notified about overnight closures in advance during the next 12 months.
Mark Fox from Highways England said: "We appreciate that roadworks can be frustrating but we'd like to thank motorists in advance for their patience while this vital improvement scheme takes place."