Bengaluru, Sept. 27 -- Thousands of ageing BS-3 buses operated by Karnataka's four transport corporations are continuing to ply on roads, raising concerns over vehicular emissions and the need to accelerate the replacement of older public transport vehicles.

The state's four transport corporations - Bengaluru Metropolitan Transport Corporation (BMTC), Karnataka State Road Transport Corporation (KSRTC), North Western Karnataka Road Transport Corporation (NWKRTC) and Kalyana Karnataka Road Transport Corporation (KKRTC) - have a combined fleet of 25,996 buses. As many as 8,786 of these buses are reportedly BS-3 models, which have higher emission levels compared with newer BS-6 vehicles.

KSRTC alone has 4,135 BS-3 buses, making it the corpo...