Nevada is investigating a construction worker's claim that he was ordered to use substandard concrete to build a highway bridge south of Reno. The worker came forward because he now believes the bridge is unsafe and at risk of collapse. "I personally won't allow my family to drive on these bridges until it is fixed because I believe it could cause catastrophic failure," he told reporters. The contractor on the job denied that substandard materials were used. "We checked out the claims that were made and in the investigation found no evidence to substantiate them," said a spokeswoman for the construction company.