That's going to be a hard question to answer since no one, really, ever knew what an interurban really was. The best definition I've seen is: an electric railway, using "enhanced" streetcar technologly, which connects two towns or cities no less than 10 miles apart, with mostly ( but not exclusively) PRW, with an average terminal to terminal speed of about 15 MPH, and which actually reaches a top speed of no slower than 40 MPH.
Most of the old interurbans, with some very notable exceptions, ran basically single car passenger trains.
The modern Light Rail System does have many of these characteristics, and the quality of its infratructure often exceeds that of the typical interurban, but, again with exceptions, tends to run multi car trains, and often runs wholly within a city or metropolitan area.
This is a question which probably cannot be definitavely answered.
Please Move to the Rear and Speed Your Ride
( Philadelphia Transportation Company)