SRT governor Prapat Chongsanguan said services between the two provinces would be suspended from Sept 16 to Oct 31 while the maintenance is done. The SRT will provide buses to take passengers from Sila-art station in Uttaradit to destinations in Chiang Mai.
The work on the 300-kilometre line will include new sleepers and tracks as well as the replacement of soil with stone under the track in four tunnels. The one-kilometre Khun Tan tunnel alone will require 15-20 days to complete.
The state enterprise is confident that after the repairs, there will be no more derailments on the northern route.
The latest derailment occurred on Thursday night, when a train bound for Bangkok jumped off the tracks at around 11pm in Long district of Phrae province. There were more than 200 Thai and foreign passengers on the train which left Chiang Mai on 5pm Thursday, but no one was injured. The SRT repaired the track and reopened services from 9am Friday.
Mr Prapat said the SRT had already negotiated with contractors and expected the total cost would be 2.8 billion baht. The budget would come from 70 billion baht already approved by the government for railway maintenance nationwide.
"The suspension of service will help speed up the maintenance, which earlier was scheduled to finish in August 2014 as workers could work on the track only four hours a day," he added.
Currently, the SRT provides 10 services in both directions on the section, six of them express trains. The train serves approximately 2,000 passengers per day so the SRT is working with The Transport Company to provide the bus services from Sila-art station to Chiang Mai without additional cost. The road distance between the two destinations is around 260km.
The full distance between Bangkok and Chiang Mai is 751 kilometres. The train journey takes 15 hours on a normal train and 12 hours for express service.
Wuttichart Kalayanamitr, president of The Transport Co, said it had coordinated with intra-provincial bus operators to prepare up to 50 buses a day to serve passengers during the rail maintenance period.