Sheffield drivers embarking on the Christmas getaway have been warned to expect major traffic congestion after lunchtime.
An estimated 1.3 million drivers on leisure trips will fight for road space with regular commuters in the UK on the last working day before Christmas.
First South Yorkshire warned drivers that traffic congestion this afternoon is anticipated to cause 'long delays' across the network.
They tweeted: "Traffic congestion this afternoon is anticipated to cause long delays across the network as today's seasonal get away combines with seasonal retail shopping and the PM peak period.
"Please plan your travel arrangements accordingly. Merry Christmas everyone, stay safe :-) ^JR"
Stagecoach Supertram tweeted: "Due to the lucky few finishing early for Christmas, we are experiencing some delays due to traffic congestion. We will keep you updated throughout the afternoon. All the best.
Dr Graham Cookson, chief economist at transportation analysts Inrix, said many motorists will find themselves stuck in long queues from Friday afternoon onwards.
Dr Cookson said it will be one of the worst days of the year on the roads with "incredibly severe" traffic jams.
He told the Press Association: "After lunch most of the roads will get busier and stay busy into the evening.
"What we see is roads in congestion for most of the time, average speeds very slow, people crawling along.
"The pure weight of traffic means a lot of motorways will be much slower than normal so your total journey takes so much longer."
The RAC is referring to the day as "Frantic Friday" and strongly urged drivers to avoid long journeys "if they possibly can".