Bulgarian traffic police estimated that December 23 would see more than 400 000 people set off on their Festive Season holidays, about half of this number departing Sofia for destinations in winter resorts and around the country.
From noon until 8pm, there will be additional lanes for leaving Sofia to help smoothe the flow of traffic.
The busiest roads are expected to be the motorway between Sofia and Plovdiv, the exit from Botevgradsko Chaussee, the road to Pernik through Vladaya and to Kalotina border checkpoint.
Sofia traffic police chief Tencho Tenev urged motorists to drive carefully, wear seatbelts and those travelling in the early mornings to watch out for iced roads.
There will be restrictions on the movement of lorries weighing more than 12 tons.
National traffic police chief Boiko Ranovski warned that repairs on Hemus motorway would continue throughout the winter, and he noted that Hemus was one of the most congested motorways at holiday times, even when there is no repair work going on.
Ranovski said that recently-approved amendments to the Road Traffic Act had been published in the State Gazette and thus were in effect as laws. These provide for, among other things, much more severe penalties for speeding and driving without a licence.
He said that every step was being taken against aggressive drivers and those who did not want to follow the rules of the road, and against speeding and drink-driving.
Statistics show that most accidents on Bulgarian roads happen between 5pm and 6pm.
Large numbers of people will be travelling by train and bus for the Christmas and New Year holidays, and state railways BDZ said that from December 23 to 27, it was providing extra coaches on trains on the most popular routes, adding up to more than 13 500 additional seats.
Reportedly, the most popular tickets were those for the Sofia – Gorna Oryahovitsa – Varna line.
Following terrorist attacks elsewhere in Europe, security at railway stations and other public places has been intensified, authorities said.