It looks like it is not such a rare occasion.
For example (link):
MUMBAI: A 25-year-old woman gave birth to a baby girl on a local train on Sunday night. The woman from Mumbra, who was accompanied by her mother-in-law, was on her way to a hospital for a check-up.
She delivered the baby at 10pm as the train pulled into Kurla. She was helped by other women travelling in the compartment. The mother and child were then taken to Rajawadi Hospital by the police.
Sometimes, children are delivered even in a metro:
This lady had a baby while waiting for a three-wheeler:
This is another story from Chennai:
In Old Delhi railway station; Tambaram railway station, Chennai; Madras Moore Market Complex (MMC) suburban railway station, Chennai; Allahabad railway junction; Ballarshah railway station, Chandrapur:
Well… given horrible regulations in maternity wards of modern hospitals, including routine artificial membrane raptures, continuous fetal monitoring, and other unnecessary things that are designed only for the convenience of the medical staff and lead to complications for women in labor, delivering a baby in a train becomes not a bad option.