Of the three options for adjusting tunnel tolls to ease cross-harbour congestion, the one which exempts public transport will be the most popular, but not most effective, experts have warned.
Truck drivers have also signalled opposition to any rise in their tolls, especially if buses were exempted.
Tunnel expert Dr Timothy Hau Doe-kwong and veteran transport analyst Dr Hung Wing-tat were commenting on the three options in a consultation document, under which tolls on the Eastern Harbour Crossing would fall while those on the Cross-Harbour Tunnel rose.
The first option decreases car tolls by HK$5 in the former and raises them HK$5 in the latter, while heavier vehicles are charged according to their resource use. The second alters car tolls by the same amount, while charges for other vehicles rise or fall according to the present structure. The third is a combination of the two with public transport tolls frozen.
Hau and Hung both said the first option was the fairest.
Hau said the last option was unfair to heavy trucks, as trucks and buses were both major culprits for congestion in the Cross-Harbour Tunnel in Hung Hom. It was acceptable to have more private cars than trucks and buses in the tunnel, because they were "much smaller and [more] flexible".
"In terms of occupation of road time and space, one truck or bus is equivalent to three private cars," he said. "If only private cars or trucks are penalised, not only will it fail to effectively divert the traffic but it also violates the user-pays principle."
Hung agreed that bigger, slower vehicles should be charged more, but said it was unlikely bus operators would switch to the eastern tunnel even if they were charged more. The first option would face most opposition, as the rate of increase for larger vehicles was the highest.
He said: "All the bus routes serve a particular community and cannot be changed easily. Raising the toll on public transport would result in higher fares."
Chiang Chi-wai, chairman of Lok Ma Chau China-Hong Kong Freight Association, said drivers picked their routes according to their destinations, not tolls. He said raising their tolls would do little to ease congestion.
"Even if the government doubles the toll of the Cross-Harbour Tunnel, truck drivers still won't switch because they always pick the shortest route," he said. "Why would they choose the eastern tunnel when they are heading for Causeway Bay or Wan Chai from the Kwai Chung container terminal? The extra diesel costs would be way higher than the money they save from the reduction in the Eastern Harbour Tunnel."
He said private cars were to blame for congestion, as the number of trucks had stayed around 117,000 while private cars continued to increase.