CHICAGO, Illinois (CNN) -- Drivers eager to get out of town for the holidays may have caused a train wreck at a crossing in suburban Chicago, the acting chairman of the National Transportation Safety Board said Thursday.At least 10 people were injured in Wednesday's crash, including seven who already have been treated and released. Three others were initially in critical condition, but their conditions have been upgraded, said the NTSB's Mark Rosenker.The wreck happened during rush hour in Elmwood Park, about 10 miles west of downtown Chicago, when a Metra express train ran into five vehicles on the track, smashing them into 11 other automobiles. (Watch the aftermath -- 3:47)The initial investigation shows that the crossing gate and safety lights were activated about a minute before the crash, and the train's engineer initiated an emergency stop "as soon as he visually saw that his grade crossing was occupied by vehicles," Rosenker said."Unfortunately," Rosenker added, "there was nothing he could do."The train was moving at about 70 mph (113 kph) -- the legal speed limit on the track -- and the engineer applied the brakes about 450 feet before the crash, but the train slowed to only about 65 mph (105 kph) before it reached the cars. (Watch Metra's reaction to the accident -- 5:27)The normal rush-hour traffic, combined with the rush to get out of town for Thanksgiving, may have led to the wreck, Rosenker said, calling the idea of staying on the tracks with the crossing gate down "a recipe for disaster."To drivers on the tracks, Rosenker issued an admonition: "You shouldn't be there."About 26,300 vehicles cross the track at the crash location daily, and Rosenker said that drivers who routinely cross the tracks there may have thought they could beat the train. "Last night was different -- different because of the extremely crowded road, perhaps because of the Thanksgiving holiday, perhaps people weren't focusing, perhaps they were thinking about a Thanksgiving dinner with their family," Rosenker said. "We were very, very lucky last night. People could have died."Rosenker said investigators plan to interview the train's crew and witnesses, as well as study the crossing, highway factors and the railroad signals.Since 1976, he said, there have been 26 wrecks at the crossing, including two fatalities in 1983 and 1997.