Motorists are returning early to avoid the congestion expected on Monday, the final day of the holiday, which started on Thursday.
Millions of provincial residents moved to the capital for work or study. Most visit their families during long holiday breaks like Songkran, while Bangkok natives leave the city in droves for vacations.
Traffic volume on Asia Highway in Ayutthaya province, north of Bangkok, rose with dawn on Saturday. It did not, however, become congested. Traffic flowed smoothly with vehicles moving at 100-120 kilometres per hour on most sections of the highway, motorists said.
On Phaholyothin Highway heading to Bangkok, traffic volume started to increase in Wang Noi district of Ayutthaya, which is adjacent to Pathum Thani, the province just north of the capital.
Police expect increased traffic on roads leading to Bangkok on Sunday as more holiday-makers return from Songkran celebrations in northern and northeastern provinces.