Motorists can now use part of the new motorway being built between Nakhon Pathom and Kanchanaburi provinces for free every Friday, Saturday and Sunday.
The Highways Department said a 50-kilometre stretch between the western Nakhon Pathom and Kanchanaburi gates will be open each week, toll free, from 3pm on Friday to 9pm on Sunday until further notice.
Other gates along the highway remain closed, the announcement said.
Opening the section would roughly reduce travel time by half, from one hour to about 30 minutes.
The new M81 highway runs from Bang Yai district in Nonthaburi province to Kanchanaburi, a distance of 96 kilometres, with a total of eight toll gates along the route.