The accident occurred soon after the train left the Dulhazara station in Chakaria Upazila
Angry locals have blocked the Dhaka-Sylhet Highway in protest.
Sarail police Sub-Inspector Abdul Alim said the accident took place around 11am on Monday in the highway’s Berhtola area.
He identified the deceased as the district Tank-Lorry Owners’ Association’s President Jahangir Alam, 45, General Secretary Ali Azam, 40, and Member Shahjahan Mia, 50.
Angry residents of the area then started demonstrating by blocking the highway, disrupting traffic on both ways, he added.
He said police were trying to control the situation and resume traffic.