The department undertook an extensive review of its testing data after a series of stories in The Sacramento Bee raised questions about testing of the concrete foundations on the new eastern span of the Bay Bridge.
In its review, CalTrans said irregularities were "exceedingly rare" and limited in scope.
"The subject matter may be complicated, but the conclusion is simple: California's transportation infrastructure rests on dependable foundations," the agency's director, Malcolm Dougherty, said in a letter to state Sen. Mark DeSaulnier.
DeSaulnier, D-Concord, chairs the Senate transportation committee and convened a hearing on the matter last year. At the time, he asked for an independent review by the Legislative Analyst's Office, a report he expects to receive in the next few months.
He said it was critical that the foundation-testing data be thoroughly examined before the scheduled opening of the new span, which is the eastern half of a bridge that connects San Francisco to Oakland and Berkeley.
The $6.3 billion bridge is expected to open by the end of the year.
"We know that the existing bridge is not safe," DeSaulnier said.
The Bee found that a CalTrans technician who tested the structural integrity of the new span's main tower falsified tests on other projects.
CalTrans said experts who analyzed more than 23,000 tests found that the results were "demonstrably unreliable" in just 11 cases. Engineers then conducted structural tests to determine whether the concrete was stable.
"In every single case, the structures were found to withstand the stresses for which they were designed," the agency's director said in his letter.
Despite its positive findings, the agency said it was implementing changes. They include subjecting test data to a quality control assessment as a way to verify the accuracy of results and requiring greater oversight of the testing operations in the field.