The world’s largest steam locomotive, Big Boy No. 4014, on Thursday began its journey out of the Rail Giants train museum at Pomona’s Fairplex, its home since 1962, to Wyoming. But it’s a slow journey, as the locomotive isn’t functional and it’s being towed as track can be laid. Friday’s column has the details. The Big Boy was the subject of a column in August. You can watch a 45-second video from Thursday here.