New crash tests have raised some concerns about how safe people are when riding in the back seat of small pickup trucks.

This comes after the Insurance Institute for Highway Safety tested five popular models with a crash test dummy in the back seat to see how well the trucks’ restraints and other safety features protect passengers during a crash.

“None of them received a good rating, and four out of five received a marginal or poor rating,” said Jessica Jermakian, IIHS vice president of vehicle research.

Of the vehicles tested, the Nissan Frontier crew cab was the only one to get an “Acceptable” rating. The Ford Ranger crew cab was rated “Marginal” when it comes to safety, and the Chevrolet Colorado crew cab, Jeep Gladiator and Toyota Tacoma crew cabs were rated “Poor.”

Jermakian said the testing was updated last year, after research showed that possible deadly outcomes for belted passengers in the back seat are higher than for those in front.

Researchers at the institute said they believed the results are not due to the back seat being less safe, but instead that “improved air bags” and “advanced seat belts” are rarely used in the back of the trucks.

While crash tests are geared toward informing consumers about cars before they buy them, Jermakian said the hope is the results will also get the attention of automakers.

“We expect the automakers to pay attention to the restraint systems in the rear seat and introduce advanced belt technologies, like pre-tensioners and load limiters that we’ve had in the front seat for years,” Jermakian said.

Despite the results, Jermakian said the guidance for parents on how to transport their children in truck has not changed.

“We know that from real-world data that children are still best protected in the rear seat,” Jermakian said.