TODAY | November 24, 2012
>> that horrific thanksgiving day pile-up in texas that involved at least 140 people. two people were killed, at least 100 others injured. two heroes emerged. tom costello had their story.
>> reporter: it took more than nine hours to clear two miles of twisted wreckage on i-10 in east texas . two dead, a husband and wife. their suv crushed by an 18-wheeler.
>> this semi was up in the air, higher than the back of my trailer. it's like he was jumping around. he was in the air, airborne, taking these cars with him.
>> reporter: police credit good samaritans with helping to save lives. katie is a nurse who rushed to help another family as the chain reaction continued.
>> i jumped in the car, sat on a little boy 's lap, closed the door and we all just braced each other until we knew it was done.
>> reporter: damian managed to free nine accident victims.
>> you really couldn't see. i just ran to the nearest car and started yanking people out.
>> reporter: the dense, fast-moving fog described as a death trap . four years ago a deadly mix of fog and brush fire smoke caused a 50-car pile-up on i-4 in florida, killing four. in california, in 2007 , dense fog caused this
100-car pile-up near fresno that killed two. and this is the time of year when fog can move in quickly.
>> you get the longer, cooler nights and that basically allowed the temperature to cool all the way down to where that moisture can condense and produce some pretty thick fog.
>> reporter: fog is notorious for distorting a driver's perception of speed and distance. experts advise to slow way down. don't forget to use your fog lights , not your high beams. and try to pull way over until the fog clears. overall, traffic fatalities continue to decline year round. over thanksgiving, 610 deaths in 2005 to a projected 451 this year, a 26% drop. thanksgiving is the single busiest travel period of the year for families, with 39 million of us driving over these four days, and sunday will be the single busiest day when so many people start heading back home. tom costello, nbc news, washington.