A state transportation department maintenance truck was hit from behind along Interstate 5 on Wednesday afternoon near Manteca.The Caltrans truck had an attenuator, or a large, yellow safety device, on its back.A witness who saw the crash from his office said the driver of the car that hit the truck is lucky to be alive."The car was at full speed when he hit the Caltrans truck," Darren Killgore said Thursday. "He sat up on his seat and he was looking around. He sat back down, and I was like, man, that guy is alive and OK."The attenuator is designed to crumple and absorb shock, Caltrans said. Killgore said the attenuator crumpled perfectly when the car hit it -- and saved the driver's life.Although the driver of the car walked away from the wreck, a Caltrans workers suffered minor injuries -- but is expected to be OK."The accident could have been much worse had it not been for the attenuating truck," said Chantel Miller, a Caltrans spokesperson.Miller said the wreck is a good reminder for drivers to pay more attention to workers on the road and slow down for any construction zones.