The government has ordered authorities to strictly enforce laws to ensure road safety on Thursday as Songkran revellers return home.
Prime Minister Gen Prayut Chan-o-cha is worried about Thais' safety during the Songkran celebration, said Col Winthai Suwaree, the National Council for Peace and Order (NCPO) spokesman.
He was particularly concerned about revellers being stranded in the provinces if transport services back home were inadequate.
The prime minister has assigned army chief Udomdej Sitabutr, also NCPO secretary-general, to deploy more soldiers to look after people, Col Winthai said.
He said 243 road safety checkpoints were set up along inter-provincial roads and main roads nationwide during the festival.
Deputy Interior Minister Suthi Makboon said officials will keep a special eye on the roads until Sunday to keep accidents down, especially in large provinces like Nakhon Ratchasima and Nakhon Sawan.
Long queues formed at bus terminals in Nakhon Ratchasima province Wednesday as revellers bought tickets back to Bangkok and eastern provinces such as Chon Buri, Chanthaburi, Rayong and Trat.
Congestion also was reported on Mittraphap Road in Nakhon Ratchasima's Sikhiu district. Special roads between kilometre markers 91 and 97 and in Pak Chong district were opened to keep traffic down.
The Department of Land Transport (DLT) has doubled the number of services on route no 21 between Nakhon Ratchasima and Bangkok to 400 round trips a day to respond to public demand.
Nopparat Karoonyavanich, vice-president of the Transport Co, said he was confident the extra services would be enough to meet demand.
It had increased the number of bus services from 6,000 to 7,500 round trips a day since the first day of the festival.
State Railway of Thailand (SRT) governor Wuthichart Kalayanamitr said the SRT has added more northeastern-bound trains with additional bogeys, which will run until Sunday.
"Eighteen trains on the northeastern route will run every day. Additional bogeys will be arranged for some routes to ensure no passengers are left stranded," Mr Wuthichart said.
Three additional trains also will be arranged for Ubon Ratchathani, said the SRT governor.
He also said train staff have been told to take enough rest because it would affect their performance and passenger safety.
Mr Wuthichart said the DLT has also provided additional 70 buses to carry more passengers back to their destinations.
During the festival, Suvarnabhumi airport has served about 160,370 passengers, with another 84,465 estimated at Don Mueang airport.
Public Health Minister Rajata Rajatanavin said the hotline 1669 received 7,455 calls for help during the holidays.