Do airways with multiple numbers (e.g., J89-101) imply combined segments? On SkyVector, I see many airways with 'multiple' names such as J16-36 or even J89-94-100-128. I can't find any information on how to interpret these names.

I'm guessing it's a convention to say that for some portion of the airways, J89 and J94 overlap - but presumably it's still valid to simply route along J94 including those shared segments?


Example near KORD
Yes, from your example J34-68-538 are jet routes that share a segment and aircraft on different routes may travel the same segments between waypoints. A complete explanation is in the FAA's Aeronautical Chart User Guide.