A sexual act that involves using a model train set to be involved in love making such as jamming the model train conductors into the urethra or fitting the entire train with its cabs into the vagina
It can also be described as thrusting extremely hard while having sex, screaming at the top of your lungs "CHOOOO CHOOOO" and cumming all over said persons face, ass or vagina
I think me and Cindy are gonna do some Train-Yard Blast tonight"