A train depot for the Purple Line opened on Wednesday but the mass-transit line is far over budget because of a decision to bypass communities.
But the recent decision by authorities not to seize residential areas for the new underground railway has increased the project's budget by five billion baht, according to the Mass Rapid Transit Authority (MRTA).
The route design now has to bypass communities by at least five kilometres, with the changes incurring additional expenses, the MRTA governor Peerayudh Singpatanakul said Wednesday.
Construction of the storage, repair and training centre in Nonthaburi's Bang Yai district is 80% complete and officials said it will be ready by the time a test run begins.
Transport Minister Arkhom Termpittayapaisith said after the opening ceremony that test runs were planned for May and June. During the trial, free rides will be offered to passengers.
The official launch for the line between Bang Yai and Tao Pun is scheduled for Aug 12 to honour Her Majesty the Queen on her birthday.
Fares on the new route will start at 16 baht and increase by two baht for every stop with the maximum capped at 40 baht. It has 16 stations along the 23-kilometre line run by electric trains manufactured by Marubeni Corp and Toshiba Corp of Japan.
The first three trains arrived on Sept 7 and 18 more will be delivered by January.
The Purple Line falls under the responsibility of the Mass Rapid Transit Authority of Thailand (MRTA), which sold a concession to Bangkok Metro Public Co (BMCL) to operate it. BMCL also operates the Blue Line, better known as the MRT subway.
One potential obstacle to success of the new line is the missing link between the Blue Line's Bang Sue station and the Purple Line's Tao Pun station. They are located a kilometre apart.
The MRTA is in talks with the BMCL to speed up construction to extend the Blue Line service for that extra kilometre to allow passengers to interchange.
Mr Arkhom said free shuttle buses will be provided for riders between the two stations in case extension of the MRT Blue Line is not finished by the time the Purple Line opens.