CB is still used some in the US, especially by long-haul truckers. Power limits are about the same as given above for the UK. It is a specific part of the rules for CB that it is intended for 2-way communication, and "broadcasting" anything for unknown listeners, especially music or relays of commercial broadcasts is specifically prohibited.

It is expected when you "key up" that you intend to talk to a another person, and expect a reply from same. The rules do allow you to ask for "someone who knows what the weather is up the road," or to ask for help with route conditions or directions. "Broadcasting" - i.e. transmitting when you don't know whether anyone is there to reply - is generally accepted to report unusual traffic conditions, accidents, unusual weather and the like. Although "bear reports" to warn other drivers of the location of law enforcement vehicles, speed traps, and/or whether the port of entry scales are open when you cross a state line, are common, but many states have their own laws that proclaim particular ones of those kinds of reports to be illegal.

A difference between using a cell phone for communication on the road versus a CB is that only the person you call on your cell phone can answer you, while a CB call can get a response from anyone within range - and a warning or information message can also be heard by anyone in range. Whether that's a useful distinction depends on how likely it is that anyone will be withing range of your CB, and the "user density" accessible to any but the "in crowd" (mostly truckers) has been in decline for some time in most parts of the US.

The intended range for CB communication is generally considered about 15 miles within the US highway systems (usually less in congested areas), but the frequency ranges used for the 40 channels are low enough that signals "aimed up" a little can bounce off upper layers of the atmosphere, and the rebounding downward pointed waves can bounce off the ground, making it possible to "talk to" people at rather large distances. Called "skip communication," it is illegal to do this deliberately (and for consistent results it's usually necessary to exceed legal power limits), but "accidents happen" if you work hard enough at setting up to have one. Without preparation, I've received fairly large fragments of conversations in Cincinnati while driving over the "divide" in the northern Rockies - about 1500(?) miles away, and there are "location pairs" that are known to have frequent long range "skips" that really are just accidents.

So far as I've been able to tell, there is very little use of "shortwave" communication of the kinds we were familiar with even a couple of decades ago. Nearly all who operate under an "amateur license" now use systems very much like cell phones, in which the amateur's radio (usually a handset) communicates with the nearest relay, and the messages are passed from relay to relay until a destination is reached (just like cell phones or the internet). There still are shortwave broadcast stations, and one usually can pick up some coast guard and ship/boat communications, but for those who don't need it as a necessary safety tool it's largely a "listeners' hobby."

John