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A U.S. Postal Service big rig flipped early Friday morning while exiting U.S. Highway 101 in Palo Alto, blocking east-bound access to Embarcadero Road from southbound 101 and delaying the delivery of thousands of letters for at least 24 hours.

The male driver, a postal employee, was not injured and there were no other injuries, Yaneth Michel, a supervisor at the Palo Alto main postal branch, said. The accident occurred at about 7:10 a.m. while the driver was negotiating the turn on the cloverleaf exit from 101 about midway on the ramp. The cause of the incident is still under investigation, she said.

The truck is the biggest one the post office has and a huge jumble of mail took about five hours for postal employees to remove. The mail must be returned to the San Francisco facility for resorting, Michel said. Customers will experience lighter than usual mail delivery on Friday but only letters will be affected. Regular mail volume should be expected again on Saturday, she said.

The California Highway Patrol was on the scene and had blocked off ramp access. The truck was towed at noon and road crews were cleaning up spilled fluids.

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