He said public transport including taxis and buses will be ready to take incoming and outgoing Songkran revellers to and from major bus terminals and airports to their destinations including BTS and MRT electric mass transit trains.
Double decker buses, having been involved in frequent accidents, will be strictly controlled, he said.
A double decker is 4.3 metres high and weighs three tones and the Transport Ministry is contemplating limiting its height to two metres.
There are currently 1,700 double-decker public buses and 4,500 others are on rental basis. They have been in service for 10 years.
Mr Chatchart said more controls and supervision for double deckers are necessary for roads with sharp curves, adding that the authorities have also been instructed to strictly control buses whose drivers are not familiar with the routes.
Most of the accidents occurred on inter-provincial roads, not highways where speeding was difficult due to congestion, he said.
Somchai Siriwatanachoke, Permanent Secretary for Transport, said at least 10 million people will commute on public transport in Bangkok and 4.1 million people travel to the provinces during the water-splashing festival on April 11-13.
He said 11.3 million people will travel on motorways or expressways.
Toll fees will be exempted from 4pm on April 10 to April 16 midnight on Motorway No.7 (Bangkok-Chon Buri) and No.9 (Eastern Ring Road Bang Phli-Bangpa-in).
On Burapa Vithee (Bang Na Km6-Chon Buri), fee exemptions are from midnight April 10 to midnight April 16.
The State Railway of Thailand has increased the number of free-of-charge coaches on 12 inbound and outbound trains on April 11-12, and 20 inbound trains on April 19-20.
The Bangkok Mass Transit Authority will arrange shuttle bus service between Mo Chit bus terminal and the Victory Monument while the Airport Link exempts fees for the aged above 60 on April 13