If you can want till after June, Amtrak should be allowing roll on roll off anywhere along the line. You will need to make reservations and since this will be a new service, you may want to contact them anyway.
If you can wait till after October then the trail should be finished from Pittsburgh to Mckeesport. Or as I said you can start from here it it will be almost all trail to Mckeesport with a few roads with low traffic.
Again if you can make departure on a Saturday, I could guide you no matter which way you chose.