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Minneapolis collapse highlights US bridge cash starvation

Last week's bridge collapse has highlighted a serious lack of maintenance for US bridges and new sources of funding are desperately needed. Damian Arnold reports.

The Minneapolis bridge collapse is only the latest in a catalogue of highway structures to collapse in the US in the last few years, highlighting a serious lack of funding for maintenance.

But will the powers that be stateside heed the latest "wake up call" and urgently address America's creaking highway infrastructure?

"I keep wondering what disaster is going to be the final wake up call?" says chief executive of the American Society of Civil Engineers Pat Nadal. "I thought Hurricane Katrina would have done it but here we are again."

Clearly something has to be done starting with the $250 million reconstruction of the I-35 bridge in Minneapolis but there are at least 150,000 bridges in the US that are dangerously under maintained and need money spent on them now.

According to the ASCE's last report card for infrastructure in 2005, there are 77,000 "structurally deficient" bridges in the US which need urgent maintenance and 76,000 "structurally obsolete" bridges which need replacing. The bill to do this is an estimated $188 billion.

The US is in middle of a five year £280 plus billion investment programme for highways and public transport but that figure needs to be nearer to $600 billion says Nadal.

Such a quantum leap in Federal funding is hard to foresee and many are predicting that taxes on petrol will have to rise to pay for urgent maintenance and replacement of bridges.

In the state of Texas, for example, state gas tax has been held at 20 cents in the gallon since 1991 and Federal gas tax 18.4 cents in the gallon since 1993. The value of this tax has since lost 30 per cent of its value due to inflation and in the meantime traffic has grown by 95 per cent. Proposals put forward in March to tie the tax to inflation foundered because they were "politically unacceptable".

Consultant Halcrow has been advising the Texas Department of Transportation on private finance models that could include road tolling to generate secure cash streams for capital works and maintenance but so far the authorities are reluctant to go forward with it.

"We are working on proposals to implement the use of private investment within Texas to close the funding gap but there has been some reluctance within Texas to fully utilise private investment," says Halcrow director Brian Howells. "The benefit of using private investment is that it will accelerate the capital and maintenance and provide a certainty of funding."

Whatever federal and state governments decide to do they better do it quick because the state of the creaking infrastructure is getting worse every year and more disasters waiting to happen says Nadal.

US Bridges less than 40 years old have some degree of redundancy because design codes were changed after the collapse of the non-redundant Silver Bridge in Ohio in 1967. But the number of non-redundant interstate highway bridges more than 50 years old is going to increase dramatically, warned Dean Bowman, member of the American Association of State Highway and Transportation Officials Highway Working Group.

The ticking time bomb is even more dangerous than it should be because historically state governments have allowed the condition of bridges to run down to trigger 90 per cent Federal funding of a replacement bridge. This rule has now been changed but its legacy left thousands of bridges in far worse condition than they should have been.

"For five to 10 years there was a financing policy under which if bridges got to a state where they could no longer be maintained, Federal government would provide 90 per cent of the cost of the new bridge," said a UK bridge engineer with long consultancy experience in the US. "It was abolished about 10 years ago but it led to a culture of non maintenance and it's difficult to throw off that sort of thought process."

To make matters worse, when bridges are inspected as the I-35 was two years ago, the engineers on the inspection teams often do not have the specific expertise to cover all types of bridge design such as non redundant steel truss construction. Last year a Department of Transportation audit of 43 bridges in Massuchusetts, New York and Texas reported that bridge inspectors miscalculated the load capacity of "structurally deficient" bridges posting weight limits that allowed vehicles that could cause structural damage.

"A greater depth of inspection is needed by people who know what they are looking for," said a UK bridge engineer with long experience of working in the US. "Steel work on bridges is notorious for being inspected by people who spend 90 per cent of their life on concrete bridges and do not pick up signs of cracking and fatigue. Often they don't pick up what is happening behind the rust."

The state of US bridge infrastructure looks bleak but whether the dollars will be invested now in preventing more disasters remains to be seen.

Box

San Francisco

The elevated MacArthur Maze Interchange that feeds 75,000 motorists a day onto the San Francisco Oakland bay bridge collapsed in April 2007 after a petrol tanker crashed into the central pier and burst into flames. US engineers told NCE the collapse highlighted the need for urgent investment in bridge maintenance.

Oklahoma

In May 2002 a 40 year old 606m multi span interstate bridge over the Arkansas River in Oklahoma collapsed after an unprotected pier was demolished by a barge, killing 14 people.

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