KMB on Wednesday retired the last of its periscope-equipped buses, with one driver lamenting the demise of the double-decker nicknamed "short pig" in Cantonese.

The periscope on the buses, which were shorter than those plying urban routes, allowed drivers to see what was happening on the upper deck. But the device couldn't compete with CCTV cameras which provide a much better view.

"The buses have been with us for 20 years, and are also witnesses to the development of the company," said KMB driver Lee Kam-fai.

"There were times when kids waved at me from upstairs through the periscope. They sometimes also knocked on the periscope's glass," he said.

"Some passengers blocked the periscope's view when they put their bags on it, so I had to ask them to move the bags to let me see what was going on upstairs."

Despite his fond memories of using the periscope, Lee conceded that modern technology does a better job.

"The periscope could only let me see the front rows of the upper deck and the stairways because its viewing angle is restricted, while CCTV cameras allow me to look after passengers in the whole vehicle," Lee said.

KMB said it had 100 short pigs in its fleet over the years.

The final one in service was scheduled to depart from Lok Fu at 10:45pm on Wednesday, bound for Kwun Tong Ferry Pier.

Two of the vehicles have been donated to schools for STEM education purposes.