Three large pickup trucks that serve as workhorses for construction crews, farmers and small business owners are not providing good protection in side crashes, according to tests conducted by the insurance industry.

The Insurance Institute for Highway Safety gave low marks to the 2009 versions of the Chevrolet Silverado 1500, Dodge Ram 1500 and Nissan Titan in side crash tests results being released Wednesday.

The Ram, equipped with standard side air bags, earned the second-lowest score of marginal. The Titan and Silverado received the lowest mark of poor when tested without optional side air bags.

When the two trucks were tested with the optional safety equipment, the Titan improved to marginal while the Silverado continued to receive a poor rating. IIHS said the Silverado's test results also applied to its twin vehicle, the GMC Sierra 1500.

"The size, weight, and height of these large pickups should help them ace the side tests just like the other large pickups we've tested. Not these three," said David Zuby, the institute's vice president. "They perform worse than many cars we've evaluated."

Zuby said occupants of passenger cars typically are more vulnerable in a side crash because their bodies are in line with the fronts of vehicles. But he said even with the higher seating positions, the trucks missed the mark.

The institute attributed the Silverado's low ratings to a combination of a poor side structure and a lack of side torso air bags. IIHS said the optional side curtain air bags worked well in protecting motorists' heads, but a person's upper body would remain unprotected even with the optional side curtain air bags.

GM spokeswoman Carolyn Markey said the Detroit automaker pays attention to the IIHS tests, but "it's also important to understand the results of a single test do not determine whether a vehicle is safe or not." She said the Silverado and Sierra received top scores in the government's front and side-impact tests.

Nick Cappa, a Chrysler spokesman, said the Ram was equipped with standard front and side curtain air bags along with anti-rollover electronic stability control. He said Chrysler engineers review third-party test programs "as part of our effort to continuously improve the overall performance of our vehicles."

Nissan spokeswoman Jeannine Ginivan said the automaker designs "all of our products to provide a high level of occupant safety in a wide range of real-world crashes, including side-impact collisions."

In the institute's side test, the side of a vehicle is struck by a barrier moving at 31 miles per hour. The barrier mimics the front end of a pickup truck or sport utility vehicle.