The Transport Department said on Monday that technology has enabled officials to charge drivers who'll be using a new Kowloon tunnel.

Last week, officials publicised plans to charge drivers of all types of vehicles HK$10 for using the Central Kowloon Route when it's fully completed in the middle of next year.

Several lawmakers were unhappy with the move as officials had not apprised them of the possibility of implementing tolls when the project was first mooted.

Speaking on RTHK, assistant transport commissioner Leung Sai-ho said the project has been in the pipeline for years and that back then the SAR didn't have HKeToll or any other electronic toll charging system.

He said it would've been undesirable to build a toll plaza, as was the practice then, in the busy areas of Kowloon.

"Back in the day you always needed a toll plaza to collect tolls," Leung said.

"If you had built one in the urban areas, it would have taken up a lot of space, affecting many buildings.

"Not that I'm saying you needed to knock some down, but at least it'd have limited the room for urban development.

"So back in the day, it wasn't even possible to [consider charging] users of the Central Kowloon Route, that's why we never brought up the topic."

Some lawmakers have counter-proposed implementing a charge of HK$8 instead of HK$10, and Leung stressed officials would continue to listen to views.

But he said setting the level at HK$10 would leave the tunnel with an estimated 20 percent of unused capacity during peak hours, which could be handy for accommodating more traffic when future new towns are completed.

The 4.7km long dual three-lane trunk road connects Yau Ma Tei and Kowloon Bay, including a tunnel of about 3.9km long.

Leung also said proposals to raise tolls for Aberdeen and Shing Mun tunnels from HK$5 to HK$8 would enable the government to cut the operating deficit for the two crossings.

He went on to say money wasn't the only issue for officials when reviewing tunnel tolls.

For example, Leung said, they dropped the idea of raising charges for the loss-making Eagle's Nest Tunnel because that would've only encouraged drivers to go back to using the busy Lion Rock Tunnel.