Most likely a 737-900 series; note the location of the TE being over the windowless section of the fuselage.
737-900 wouldn't be able to make that length of flight. Rome - Chicago seems to use a 767 aircraft..
This 737-900 would likely be used for domestic flights or hops to mexico/canada destinations.
Neither of United's 777 or 767's liveries match up..
As well, it's standard operating procedure that vehicles do NOT drive under the wing- even though a low to the ground vehicle likely could, it's a big NONO.
whoops, meant to attach another 737 as well..
I've had a case where CONdolezza Rice was flying on a flight once (during jugear's admin); she was driven to the aircraft on the tarmac and boarded through the ramp access on the jetbridge prior to anyone else.