HOUSTON (KTRK) -- New video of an attempted rescue from a water-filled underpass during last week's flood shows firefighters' exhaustive efforts in a dangerous situation.The Harris County Toll Road Authority was alerted to an 18-wheeler that had driven into a flooded underpass on the North Sam Houston Tollway East feeder road at West Hardy Road around 12:30pm.Roadways cameras found it and zoomed in. Before anyone was able to get to the big rig, the video shows it floating sideways, carried by a swift current."All the roads were acting like miniature rivers," said Assistant Chief Ed Venegas of Aldine Fire and Rescue.Passers-by did their best to break through the cab with a small sledgehammer before Venegas arrived on scene."They said there's somebody in there. They saw him go in, saying, 'I can't swim, help me,'" Venegas explained.The situation was dire. The water was so deep, it touched the bottom of the overpass. Traffic signals were barely visible.Venegas was joined by other firefighters."I am this guy here setting up the rigging system," said Venegas, narrating the video.They worked to send one man down to the truck cab in a harness with a saw."We figured if we could get him out, even if he's out, we could do some CPR and bring him back," Venegas recalled.The truck kept shifting and the water was too unpredictable. After more than a hour, they had to give up."It was way too dangerous. I just couldn't afford to continue to risk everybody's life," he said.The driver was later identified as Pedro Morales, 61, of El Paso. Perhaps he was unfamiliar with Houston's flood-prone roads, because this one has been a problem, according to Venegas.Besides turning around, if there is anything learned from the video, Venegas says it's to try to get out even if you can't swim."Try to get out of the vehicle. Wait until the water pressure evens out inside and out to try to open the door. If it doesn't open at first, try again. Try a third time and a fourth time. You have to keep trying."Venegas says it was tough not being able to get to Morales that day, but they did have success later. Around 5:45pm, They rescued a mother, father and their 6-year-old daughter clinging to a pipe near Greens Bayou. Eastex Fire and Rescue assisted with a boat.