Ombudsman Jack Chan on Friday called on the Transport Department to improve transparency when it has to switch between toll points at the Western Harbour Crossing and enhance information distribution.

The call came after Chan's office received three complaints from drivers who said they were charged higher-than-expected tolls when they crossed over to Hong Kong Island in February and March during morning transition time slots, which is when the cost of making the crossings gradually increases to the peak-hour charge and decreases after those hours have passed.

"They noticed that the toll information display [at the toll point] at the Kowloon entrance did not show the real-time tolls, and the tolls charged were slightly higher than what they understood as the usual rate," Chan said.

"One of the complainants called the HKeToll customer service hotline to enquire about the matter, but frontline staff were unable to provide the precise location of the toll point."

Chan said the complainants had criticised the department for its lack of transparency as well as the confusion caused by its switch from using one toll point to another without prior notification to drivers.

The Ombudsman found that the department had deactivated the primary toll point on the southbound lane of the crossing between January and March due to roadworks and activated the backup.

"It is understandable that the relocation of a toll point is required for operational needs," Chan said.

"However, the Transport Department would merely turn off the toll information display to indicate that a toll point was inactive.

"We consider this practice unsatisfactory."

The typical distance between the primary and backup toll points is about 200 meters at other tunnels, Chan further noted, but the separation at Western Harbour Crossing is about two kilometres apart – one at the Kowloon entrance and the other at the Hong Kong Island exit.

"As a result, there is a noticeable interval between the times for those vehicles passing through the two toll points during the transition time slot, thus affecting the toll charged," the office said.

It made nine recommendations to the department, including exploring more effective ways to distribute information about toll point switches and setting out operational guidelines for staff.

The Transport Department said it would notify the public of such relocations by displaying a conspicuous banner on the HKeToll website and mobile app, its website and the HKeMobility mobile app, and on signs along the roads.

It would also revise its practices over the toll information display while strengthening staff training.