INVESTIGATIONS INTO the collapse of a section of a 3.8km viaduct in Texas on 15 September were focusing on fact that only two of its 146 piers had protection against shipping collisions.
Eight people died after a tugboat hit a pier of the 3.8km Queen Isabella causeway over the Laguna Madre, bringing down two 24m sections, and plunging vehicles travelling on 26m into the waterway.
A third 24m section collapsed later.
The tugboat involved in the disaster had strayed between 100m and 150m to the left of the navigable channel as it headed north towards the Mississippi.
The warning on bridge bashing had been well aired in the US, most notably in 1983 when 47 people died after barges hit a rail bridge in Alabama.
At the time Mike Knott, a leading bridge engineer and past president of the American Society of Civil Engineers, warned that thousands of American bridges were 'sitting ducks' with unprotected piers, risking collapse from vessel collisions.
The Queen Isabella Causeway is well defended on the navigable channel, explained US Coastguard spokesman Robert Wyman. 'There are large fenders around the piers on the navigable channel, but where the tugboat hit there was no fendering.'
The boat's owner, Brown Water Towing, issued a statement saying the vessel struck an unmarked sandbar within the channel that caused it to veer off course and that navigation lights were not working correctly.
The Coastguard rejected the claims. 'After the accident we checked all Coastguard maintained aids to navigation and all were found to be OK, with no discrepancy notices issued in the last three weeks, ' said Wyman.
And a US Army Corps had surveyed the channel the following afternoon found everything in order in the 4.3m deep channel.
'Based on preliminary results there is no evidence of shoaling or anything that might have affected the depth of the channel, ' said Wyman.
The four lane causeway was constructed in 1974 at a cost of $11M using prestressed concrete beams and reinforced columns.
It is the only bridge linking South Padre Island with Port Isabel on the mainland. The collapse also severed telecommunications links and the island's water supply.
The Texas Department of Transportation has let an emergency contract to rebuild the collapsed spans.