The incident, on Saturday, occurred six days before the first anniversary of the I-35W bridge collapse in Minneapolis, which killed 13 people (NCE 9/16 August 2007).
A 2.7m by 1.8m by 25mm thick veneer fell onto two cars, but caused no injuries. The I-35 east in St Paul, which neighbours Minneapolis, was closed for eight hours while the Maryland Bridge was inspected and loose delaminated pieces of concrete were knocked off.
Age, freeze-thaw cycles and salt have been blamed for the deterioration in the 50 year old bridge.
"At this time it is unclear if there will be any additional work needed," said an MNDoT spokesman.
"We plan to conduct a more extensive inspection within the next few weeks to determine if there are any additional repairs needed. At this point, we have taken care of the immediate problem and it is safe to travel beneath the bridge."
The I-35W collapse last August highlighted the poor condition of US infrastructure and pushed infrastructure maintenance up the political agenda.
The US House of Representatives endorsed two American Society of Civil Engineers backed bills last week. Legislation to improve inspection requirements and authorise £1bn in funding to repair deficient bridges was passed. More legislation to restore £4bn to the Highway Trust Fund to keep it solvent through the 2009 fiscal year were both passed. Both bills are now heading to the US Senate for consideration.