Concern is mounting over the safety of guardrails sold by Trinity Industries, as yet another state has threatened to stop buying them, and will consider removing them.

Virginia, in a letter sent to the company on Friday, told Trinity that state transportation officials did not believe Trinity had properly tested the end of a guardrail it redesigned in 2005. Virginia officials also told Trinity, which is based in Dallas, that the company had made changes to the design without telling them.

If the company does not conduct new tests, in the presence of Virginia officials, and provide proof to the state’s Transportation Department by Oct. 24, the state will ban the product, officials said.

“We’ve given them a deadline to provide the research we’re asking for,” said Marshall Herman, a department spokeswoman. “If they can’t prove to us it’s safe for use on Virginia roads, then we’re not going to use it, and we’ll begin to inventory where the product is installed and look into removing them.”