Workers at a nearby plant heard the crash and ran to help. "We started to go through the trains cars to try to get people out,Â" said one of the workers.
Amtrak says both of the trainÂ's engineers, another employee and 15 passengers were injured; most suffered minor bumps and bruises.
It is the third Amtrak accident in a week and the second at a rail crossing. On Tuesday, Amtrak's Silver Palm hit a car and van in Boca Raton, Fla.
The eastbound Sunset Limited was traveling from Los Angeles to Orlando, Fla., when it collided with the rig and derailed at 11:43 a.m., in a rural area of Colorado County 62 miles west of Houston, Steven Taub, an Amtrak spokesman, said.
About 800 feet of track was torn during the accident. At least two engines and seven cars were off the tracks.
The two crewmen were the most seriously hurt, said Texas Department of Public Safety spokesman Mike Cox.
An engineer and an engineer-in-training had to be pulled from the wreckage by rescuers who broke out the engine windshield, said Jason Goggans, the assistant conductor on the train.
"I felt the brakes go into emergency before we actually hit," said Goggans, 48, of New Braunfels, who was in an office in a crew car at the time of the wreck. "You just grab on. You don't know what to expect. We knew something was going to happen."
It took about 20 seconds for the train to stop but there was no panic as the passengers got off, he said.
"They were more or less kind of in awe," he continued. "They couldn't believe it."
The passengers included the wife of Arizona Sen. John McCain and their son, Jack, 13. Neither was hurt. They were on their way to Florida on vacation.
The truck was pulling a trailer, Cox said. The driver was not hurt.
Thursday's collision comes just four months after the deadliest crossing crash in Amtrak's history. Eleven people were killed in March when the City of New Orleans slammed into a truck in Bourbonnais, Ill.
By far, most rail accidents happen at crossings. In 1998 there were more than 3,500 - almost ten a day. The crashes left 431 people dead and more than 1,300 injured.
The accidents have brought renewed calls from safety advocates for motorists to pay more attention at crossings. While federal investigators still have not placed blame for the latest collision in Texas, it's clear Amtrak had the right of way.