The down-bound train arrived at its destination. Then it turned around for the return trip. (Or the train turned around upbound.)
These are OK, except that we don't really say 'upbound/downbound'. You could say, informally, 'the up train', 'the down train'. We also speak of 'the northbound train', 'the southbound train'.
I had a job, I had a girl I had something going mister in this world I got laid off down at the lumber yard Our love went bad, times got hard Now I work down at the carwash Where all it ever does is rain Don't you feel like you're a rider on a downbound train