Westbound traffic out of downtown Dallas will be seriously snarled today, thanks to the sudden appearance of a 2- by 2-foot hole in the right lane of Interstate 30 Trinity River bridge, just off Interstate 35E.

The Texas Department of Transportation has closed the lane, but it is expected to reopen by 9 p.m.

TxDOT spokeswoman Kelli Petras said the bridge's age and worsening condition combined with Wednesday's rainy weather to produce the hole. She said engineers believe the bridge still is safe for vehicles using the one remaining open lane.

A team of engineers is inspecting the bridge, Ms. Petras said.

The 51-year-old bridge carries about 65,000 vehicles per day. It was last inspected in 2004, and received a score of 66 out of a possible 100. A score below 80 indicates that the bridge may need significant repairs. A score below 50 could mean the bridge should be replaced.

The damaged bridge was deemed “functionally obsolete" in its most recent inspection, meaning it should be replaced or improved because it no longer is adequate for the traffic it handles. However, it was not considered “structurally deficient,” a more serious designation that suggests the bridge may no longer be safe.