A congressional watchdog on Thursday accused federal highway officials of poor oversight of the safety testing of guardrails and other roadside equipment, in a report based on a yearlong investigation.

The study, by the Government Accountability Office, the investigative arm of Congress, was done mainly in response to concerns about a widely used guardrail system alongside the nation’s highways. In crashes, the rails have sometimes acted like spears, capable of impaling drivers and passengers.

Lawsuits say the guardrails were to blame for at least five deaths, and many more injuries, in at least 14 accidents nationwide. The guardrails, known as ET-Plus, are made by Trinity Industries.

The report criticized the testing process used by the Federal Highway Administration, and called on the agency to take steps that include ensuring there are no conflicts of interest between companies that make the roadside equipment and the people who test it.