Yes, this is rust (Cedar-Hawthorn Rust, most likely, and not just because it happens to be on a hawthorn tree). Most host plants that rust fungus can infect tolerate the disease well, as it mostly only impacts fruits and young twigs. Once symptoms manifest, treatment is not possible since fungicides are preventative measures only, not able to cure existing disease. While preventative sprays next year might suppress the fungus and minimize infection, they are generally not recommended, in part because the trees don't suffer too much from it (other than being an eyesore, perhaps), and in part because fungicides can be a hassle to use effectively and the residues might harm pollinators or other organisms. It would need to be applied around April and re-applied as often as the product label recommends to cover about a 8-10 week infection window period.

You can trim off rust-infected twigs if you prefer, since they will die back to the spore-covered swollen area anyway within the year, but no other action is needed at this point. The spores the fungus is releasing now are only capable of infecting the other host plant for this kind of rust, which is Eastern Redcedar (Juniperus virginiana), along with potentially a couple other juniper species. Eastern Redcedar is native, valuable to wildlife, and abundant in open sunny areas where woods were cleared (like along highways). In early spring, mild wet weather prompts infected junipers to release their rust spores, which then travel on the wind to certain rose-family plants that are vulnerable to rust. These include hawthorn, serviceberry, crabapple, apple, quince and a few others. Therefore, the spores floating off the hawthorn now will not pose a threat to any other non-juniper plants in the landscape. (Other rust fungi can infect other plants, but they don't share this particular life cycle, so any overlapping appearance will be coincidental.)

Miri