Commissioner for Transport Rosanna Law on Saturday said new cross-harbour tunnel fees may not have an effect on traffic flow and are only a transitional arrangement.

But Law told a radio programme that the changes could see a handful of drivers switch from using the Cross-Harbour Tunnel to the Western Harbour Crossing.

From August 2, motorists using the western tunnel – which will be taken back by the government on the same day – will only have to pay HK$60 instead of the current HK$75.

However, the fee for private cars travelling through the Eastern Harbour Crossing and Cross-Harbour Tunnel will rise to HK$30 under the new tolling arrangement also known as "633".

There will also be a flat-rate charge of HK$25 for taxis for all three tunnels, with passengers having to pay double if they take a cab anywhere other than at a cross-harbour taxi stand.

"The '633’ fixed toll is a transitional arrangement. The actual impact [on traffic] will come when the time-varying tolls [are] introduced," she told reporters after the radio programme.

"I believe the pattern of driving and also the choice of routes of motorists would be different from now. So we need some time to actually monitor their behaviour and change of traffic pattern, before we can consider any further announcement of the dates of time-varying tolls."

She added that the Cross-Harbour Tunnel saw 2,000 more vehicles per day after the introduction of the new electronic auto-tolling system, HKeToll.

On suspected abuse of the HK$2 transport fare concessions, Law said about 970 people were checked for allegedly using the scheme improperly, with one case referred to the police.

She said the government will later require all beneficiaries of the HK$2 scheme to use their own JoyYou Card for public transport to further ensure only people aged 60 and over or those with disabilities are making use of the heavily-subsidised fares.