Road congestion is expected to worsen today and transport experts are warning of a traffic 'time bomb' unless urgent action is taken to better distribute vehicles among the three harbour tunnels. The warning comes after Sunday's toll increase in the Eastern Harbour Tunnel sparked fears of gridlock on other routes. Today is expected to be particularly hectic, with Fridays usually the busiest day for delivery trucks and out of town travellers. The Observatory has also forecast showers and thunderstorms, which could further slow traffic. 'Fridays are the busiest for goods vehicles because most companies try to get their orders before the weekend,' said Stanley Chiang, chairman of the Lok Ma Chau Freight Association. Traffic in the Western Harbour Tunnel and Cross-Harbour Tunnel stayed at the same level as of yesterday afternoon, but motorists continued to shun the eastern harbour route. The Transport Department reported a 20 per cent drop, or 13,369 fewer vehicles, using the eastern route as of 8pm last night. The number of cars using all three tunnels had fallen by 6 per cent, or about 7,600 vehicles, by 3pm compared with a normal Thursday. Many drivers have apparently taken to public transport amid dire warnings about traffic. Hung Wing-tat, a Polytechnic University engineering professor who specialises in transport and traffic modelling, said traffic at the tunnels needs to be distributed evenly so resources were not wasted on the eastern and western routes. 'It's a time bomb. If this problem isn't solved, it will continue to waste societal resources. We need to divert the traffic,' he said. Professor Hung said the government should take its own advice and solve the problem by raising the toll at the Cross-Harbour Tunnel in a profit-sharing agreement with the other tunnel operators.