National Express West Midlands (NXWM) has said that the average speed of some of its services in South Birmingham is now less than 6mph.
The operator blamed increasing congestion for the slowdown in speeds, and said that journey times are up to 10 minutes slower than three years ago. To maintain frequencies, 47 buses to the fleet have been added.
NXWM expressed concern that frustrated passengers could switch back to their cars, leading to further congestion problems and worsening air quality. The company is consulting bus users, the city council and Transport for West Midlands on how to improve things.