Police said that at least 10 others have been injured in the mishaps, involving buses, on Wednesday.
Two of the dead have been identified as a 40-year-old woman Jesmin Akter and Md Zulfikar, 60.
The other victim, estimated to be 35 years old, is yet to be identified.
Highway Police’s Sergeant Nizamul Fahmi said a Chittagong bound bus from Dhaka lost control on the highway at Sitakunda and rolled over on the road divider.
“Zulfikar and the unidentified man died on the spot; at least eight others were injured in the accident which occurred around 6am,” he told bdnews24.com.
In the port city, a bus hit a tree on a street near the polo grounds around 11am.
Traffic Sergeant Md Jalil said that three passengers were rushed to the Chittagong Medical College Hospital where the doctors declared Jesmin Akter dead.