A man was arrested on Monday in connection with fires on train carriages in and around Johannesburg, Metrorail said.
This brought to six the number of arrests in connection with vandalism and the torching of trains, spokesman Lawrence Venkile said.
"The man is employed by Metrorail as part of its shunting personnel and is expected to appear in court soon."
Five men were arrested on Thursday, after six trains were burned in New Canada, the Braamfontein yard and the Elandsfontein yard in Leralla on Wednesday night.
Another three train carriages were torched at the Orlando East railway station in Soweto on Thursday night.
Metrorail and the Passenger Rail Agency of SA (Prasa) blamed striking workers for starting the fires.
Venkile said two of the five men already arrested were expected to appear in court on Monday for a formal bail application.
"We will be opposing bail because the nature of the crime is serious... We do not believe that they will not try a further sabotage of the system or try and influence others to do the same."
The estimated cost of damage was about R70 million, Venkile said.
On February 27, SA Transport and Allied Workers' Union members went on strike demanding the dismissal of Prasa CEO, Lucky Montana.
About 3000 workers in Tshwane and Johannesburg are on strike, as well as workers in the Eastern and Western Cape.