We once had a 30 mph train with two tanks coupled together. They both were equipped with tightlock couplers. The trailing truck of the lead car derailed and came out from under the train. The truck was drug by the brake rod OUTSIDE the rails where first it struck a vertical 6" steel post, then across a diverging track and finally across a signaled crossing. The brake rod clevis pin finally broke 1/2 mile later and the truck sailed out into a wheat field. The train crew was unaware until the dispatcher was notified by the elevator crew who called and said something was "wrong" with the train! When I came to relieve the crew who had gone on the law I was looking at two tanks supported by three trucks. Always stay at least 10' from the track! JP