Simple answer depends on what you mean by "shared."
Running on the same tracks with trains intermixed? No, absolutely not. Passenger trains in that kind of service have to meet FRA railroad safety and other standards, and are anything but "light" rail.
Otherwise, light rail and freight rail can share tracks if they are time-separated: freight runs during time blocks (at night) when there is no passenger service. Current examples of that are in the San Diego area: the line between downtown and the border, up to El Cajon, and the Sprinter service between Oceanside and Escondido. There may be others but they don't spring to memory right now. San Jose once had it, with freight using part of the Orange Line between Caltrain near the Mountain View station and Moffett Field; long gone.
They can also, of course, share right of way using separate tracks. That happens in many places, since light rail in the US commonly was built on abandoned or lightly used rail r/w. Freight rail in the US has been actively downsizing since the 1980s, so many lines were sold off or there was space available in a r/w that once had multiple tracks to add light rail. Those are hardly desirable locations from the standpoint of surrounding land use and station sites, but they were (sometimes) cheap, and (often imaginary) cheap was a major draw of light rail.
You do have to remember that light rail in the US is not light rail in Europe or many other places. In the US, it's used functionally as a (often not very) limited-stop bus line, with average (with stops) running speeds barely exceeding those of an on-street BRT line. So maybe the iffiness (is that a word? It is now...) of some of those station sites is understandable since they are basically big bus stops.
A special case of sharing is where light rail crosses an active freight track at grade. Some kind of interlocking signaling is usually needed in those cases, even if the freight track is lightly used. A lot of older systems in the eastern part of the US have one or more of those. Even Sacramento had one, for a while, on its Green line.
As usual, there are documents (and regulations). Google (can be) your friend. For instance: [
www.transit.dot.gov]