ENGINEERS IN the US this week seized on the freak collapse of part of the MacArthur Maze interchange in San Francisco to stress the vulnerability of the nation's highway infrastructure.
The interchange, which feeds 75,000 motorists a day onto the San Francisco-Oakland Bay Bridge, collapsed in the early hours of Sunday morning after a petrol tanker crashed into a central pier and burst into ames (see box).
US engineers who spoke to NCE said the crash highlighted the absence of redundancy on some of the nation's key transport corridors and reinforced the need for urgent investment.
California Department of Transportation (Caltrans) engineers have warned that the damage could take 'months' to repair, leaving one of the nation's busiest roads in a state of near paralysis.
The US Congress is currently consulting on a new national transport policy, the first since the interstate system was introduced by President Eisenhower in 1955.
Dean Bowman, member of the American Association of State Highway and Transportation Officials Highway Working Group who is working up the highways component of the congressional commission, explained the need for more investment. 'Most interstate bridges were built between 40 and 50 years ago, so in the next few years the number of bridges over 50 years old is going to increase dramatically. The gap between need and investment is getting bigger.' The US is in the second year of its largest ever transport investment programme, after president George Bush guaranteed $244bn (£122bn) funding for highways, highway safety and public transport.
But its $59.4bn (£29.7bn) annual spend is still way short of the $94bn (£47bn) needed to bring the network up to standard, said Gabe Norona, senior vice president of engineering software firm Bentley.
The US Department of Transportation says there are 77,000 structurally deficient bridges across the country, with a further 80,000 deemed 'functionally' deficient by being either too narrow or too low. It estimates it would cost $9.5bn (£4.8bn) to repair over 20 years.
It happened here
An overbridge on the M25 in Surrey avoided collapse in 2003 when its was struck by an articulated lorry carrying timber plastic and foam.
The lorry burst into flames, damaging the post tensioned Oaklawn Road bridge. The motorway was closed and temporary props installed to bolster the damaged pier (NCE 6 March 2003).