HOUSTON – A crash involving a tractor-trailer and another vehicle Tuesday caused a hazmat spill that closed the westbound lanes of Katy Freeway at North Post Oak Road for several hours.

The crash was reported around 7:45 a.m.

Officials said that less than a quart of formic acid spilled from two containers on the tractor-trailer, but crews must move the acid to new containers before the cleanup can begin.

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The acid, which is commonly used in livestock feed, is not a threat to the public, officials said.

The cause of the wreck is under investigation.

The road was closed during the start of rush hour. Several lanes reopened shortly after 5 p.m.