By trauma, do you mean a trauma surgery rotation? Are you going into EM or gen surg-->trauma surg? I ask this because if you come to U of MD, get ready for q3 call and several hours of rounding each morning. You'll get to do procedures in the TRU (as a 3rd year I got to put in a couple A-lines, *attempt* a central line (did not get it on first try and resident took over), lots of suturing lacs, lots of general trauma evals/C-spine evals, tons of FAST scans, and maybe 2 ultrasound-guided IVs), but a lot of the really "cool" stuff is going to get snapped up by the residents. The OR is "optional" for students doing electives (those interested in emergency med and not surgery usually opted not to go to the OR).
The thing about the trauma experience at Maryland is that once your patient has been stabilized and surgerized, they can then sit on your team for relatively long periods of time, and you have to round on them every day. Most of them are pretty complicated and involve multiple consultants so it's not unusual to spend 30 mins + on each patient (and, depending on your team, you usually have 20++ patients at any given time upstairs, sometimes MUCH MORE). Usually what you are then managing is routine stuff for the not-so-sick/moderately sick patients (medical issues, calling consults/checking consult recs, making decisions about PEGs/trachs, etc. - trauma is a huge dumping ground for ortho, neurosurg, etc...they do all of the surgery for many of the trauma pts, and then they just leave them with your team to manage them from day to day, while they continue to consult daily. There are NPs that help take care of a lot of this stuff, but ultimately your team is responsible for coordinating everything for each pt.) If they are really sick, they go to the trauma ICU, where they have a dedicated TrICU team who takes over their medical and day-to-day management. Also, anesthesia is always a quick phone call away. Thus, if something happens while you are in the TRU/OR/home/otherwise off the floor (the pt needs a chest tube, the pt needs to be intubated, pt needs a central line, etc.), the ICU team or Anes is going to do the procedure. You will do some procedures on/after rounds on your pts hanging out on the floors, but mostly pulling staples/pulling chest tubes out/changing wound vacs (sometimes this is done in the OR)/re-dressing wounds/etc. I didn't do any more complicated procedures during my trauma rotation on patients that were already upstairs (although we had a couple of "dedicated ICU days" and I got to assist on a central line on one of those days.)
My biggest gripe about trauma was the sheer number of people on the trauma team. We had 4 MS3s, 2 sub-Is, 5-8 junior and senior residents (both EM and surg/surg subspecialty), a fellow, and one attending at any given time. As the medical students, we were low enough on the totem pole that we were always last in line for cool stuff. Even our sub-Is didn't do much as we did because 1. they worked fewer total hours than the 3rd years did, 2. they were not interested in trauma SURGERY as they were going into EM, so they stayed in the TRU most of the time and didn't go to the OR, and 3. it was January/February and they were sorta "checked out".
If your goal is to do lots of procedures (central lines, A-lines, inbuations), your best bet would probably be to do an ICU rotation, like the SICU. However, if you are interested in trauma SURGERY, then things change a bit.
One of my classmates is wrapping up a trauma surgery sub-I currently. I'll point her to this thread and perhaps she can give you some feedback re: procedures.