M4 and M5 works under way in Bristol and Gloucestershire
Work will begin later on the £88.6m project to introduce variable speed limits to two motorways near Bristol.
Overnight preparation work starts on 12 January between J19 and J20 on the M4 and J15 to J17 on the M5.
The "managed motorway scheme" will use variable speed limits and the hard shoulder to ease congestion.
Elsewhere, three months of safety improvement work has begun on the M5 in Gloucestershire between J13 and J14.
Speed restrictions and narrow lanes are in place while a new concrete central reservation barrier is being installed.