The Hagenbeck-Wallace circus train was moving through Hammond, Indiana on June 22, 1918 when it was hit from behind by another train, which was pulling 20 cars. Although the second train was moving at only 35 mph, it was a metal train --- and when it hit the circus train, it wrecked several of the wooden train cars, and a fire broke out (because kerosene lamps were used to light the circus cars at the time). 86 people were estimated to have died, and another 127 were injured. The actual number of people killed is truly an estimate -- the fire burned so hot that it was impossible to identify all of the bodies, or identify how many bodies there were. A number of the grave markers had no name on them, and are marked as "Unknown Male No. 30," for example, because it was common back then for people to join up to help with the circus right before a performance, and not be recorded as circus employees.
I found it very touching that the Showmen's League had taken care of all of these victims, and the entire Showmen's Rest area is very nicely maintained. You can read more about the wreck here on the Showmen's League site, and also at Wikipedia.