Plans to impose time-varying tolls at Tai Lam Tunnel could help it reach full capacity, an official said on Thursday.

Speaking on an RTHK programme, the Transport Department’s Assistant Commissioner Leung Sai-ho noted that if the tolls for the tunnel connecting Ting Kau and Yuen Long stay at their current levels, there would still be about 15 percent capacity untapped by 2026.

He said authorities hope the adjusted tolls would attract drivers to use the tunnel and help disperse traffic flow on alternative routes.

"We were thinking about how we might utilise remaining capacity and help spread traffic for different routes. People may be familiar with Tuen Mun Road and Tolo Highway. If we adjust the tolls, we hope to attract more drivers to use the Tai Lam Tunnel, which is the most crucial factor in our consideration," he said.

The proposed changes will include three tiers of charges for “peak”, “normal” and “non-peak” hours, similar to the system used for the cross-harbour tunnels.

Instead of the present fixed toll of HK$58, private vehicles would pay HK$45 during peak hours, HK$30 during normal hours, and HK$18 during non-peak hours.

Asked whether there was room to further lower the charges during peak hours, Leung said authorities had been very careful in setting toll levels, warning that if tolls are lowered again congestion may occur.

The official also mentioned that the fall in tolls for commercial vehicles - down from current level of between HK$64 and HK$79 to HK$43 throughout the day - is quite high.

He stressed that data shows that Tai Lam Tunnel is heavily used by vans and trucks, indicating that the logistics industry relies on it to travel between the northwestern New Territories and urban areas.