Two lanes are closed on the M40 southbound for an emergency barrier repair causing a 60-minute delay above usual journey times.
Contractors have been on the scene between J5 (Stokenchurch) and J4 (Handy Cross) since early this morning.
Highways England tweeted at 7.50am: "#M40 Southbound J5 to J4 - Lane 3 closure is in place for an emergency barrier repair. Contractor on scene dealing, lane closure signals have been set."
Just after 9am, the roads agency tweeted again to say a lane 3 closure was in place on both the south and northbound carriagways, with a second lane closed off going southbound just after 10.50am.
Drivers are being advised to "approach with caution", with Highwawys England saying just after 12pm: "There are 60 minute delays on the approach to this #M40 incident above usual journey times spanning 3.6 miles back to J5 for #Stokenchurch.
"Average speeds on approach to the incident are less than 10mph."
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