>Freight and light rail physically cannot share the same tracks by definition.

Doesn't the River line light rail share tracks with freight?

Although go into the posts about the IBX on r/r/nycrail if you want to see all the arguments about what the definition of light rail is. It's not a scientific term so it doesn't actually have a specific definition in that regard and legally the definition is just that the train cars look like trams:

>Light rail means a streetcar-type vehicle railway operated on city streets, semi-private rights-of-way, or exclusive private rights-of-way. Service may be provided by step-entry vehicles or by level-boarding.