We always go but then its close for us! And we usually go on a weekday when the traffic isn't a big problem.
If you have to go on a weekend then the backway we use probably the most is Walnut street... In Greencastle Walnut street turns RIGHT one block south of the light where US231 goes around the town square and it goes all the way to Mansfield more or less directly. If you turn onto county road 775E that comes in behind (South-East) Mansfield right where Jim's parking is and they give front row parking to bikes - right by the dumpsters and porta-pots!
Google Maps Link
I will warn you that the road isn't the best and a lot of people know this route so it won't be empty by any means.
If you take US36 and get bogged down in traffic you can also take 875W
(Left at the "CREEKSIDE" sign, the LEFT right before the Portland Mills sign points you RIGHT on 880W. No assurances to the road uality I've not been that way in years...
Those going to Bridgeton also note that take Mansfield Road out of Mansfield to get to Bridgeton over the summer they reworked several patches through the bottoms and they were oiled and sanded.
between Rockville and Bridgeton is also a good drive and the pavement is in pretty good shape there.
I-70 is jacked up with construction and pushing a LOT of traffic onto US40 so US36 MAY
be a better route....
Lastly - I think - anyone planning to RIDE the bridge route stick to the routes SOUTH of US36 as they're paved where the northern routes have a lot of sand and gravel. In the cage the northern routes have some very nice bridges especially Jackson which was recently rebuilt (Yellow route)