In "The Dark Knight", why did the cops want to evacuate Harvey Dent from the hospital in an empty bus?

Question

After the Joker threatened to blow up a hospital, and doctors and cops in Gotham General (the hospital in which Harvey Dent was kept) started to evacuate patients, a cop said to another cop named Davis, "I'm gonna find a bus for him," referring to Dent, and went out. Only after all the patients except Dent were evacuated, that cop said to Davis in the police radio, "They got space, Bring him out" - but wasn't responded. He hurried back to the hospital looking for Davis, but was shot by the Joker, who has disguised himself as a nurse.

My question is, why was it important to find for Dent an empty bus (Not necessarily completely empty, but mostly)? I tried to figure it out, and I have two possible answers, but they seem pretty weak to me. The first one is that it was for Dent's own safety - he was already injured, and the cops didn't want him to be on a crowded bus where he can be harmed or infected by others. The second one is that the cops didn't want Dent to harm others, because they have already noticed his vengeful desires.

Whatever the reason is, I think it's not established enough, because of another thing that wasn't clear (at least to me): Dent's current status in the eye of the police - was he still considered the White Knight, or was he already considered a potential murderer. Later in the film Gordon was worried about not finding him, but it doesn't strike to me from which reason.

Answer 1

I do not believe that they wanted to reserve an empty or mostly empty bus for Dent. I believe they simply wanted to move him from the hospital room (which they thought was a secure location) to a bus ready to depart and to do so with minimal time in between. At this point, Dent's severe burns put him at a significant risk of infection, and they want to keep him in as controlled an environment as possible in order to fend off future attack or kidnapping attempts by the Joker. (Clearly they failed in this effort.) They just wanted to avoid having Dent wait around in the parking lot while they walked around asking about seating availability, so they secured a seat before bringing him out.

Answer 2

You missed a line earlier in the film.

Gordon: I want you to call in every officer. I want them to head to their nearest hospital and start evac and search. Call the Transit Authority, School Board, Prison, get every available bus down to a hospital. The priority is Gotham General

So basically the officers are trying to find him a space on an(y) outgoing bus, as we see a few minutes later.

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This tallies nicely with the film's official novelisation which gives a very slightly different account of the dialogue. Dent is a "VIP passenger" and they don't want him left waiting when there's bomb about to go off.

Detectives Jeremy Polk and Willy Davis were on the four-to-midnight shift outside Harvey Dent’s room at Gotham General when the word came to get everyone out, and that meant Harvey Dent as well, ASAP. Polk and Davis checked the room, then Polk left Davis standing by Dent’s bed while he went to the street outside to see what he could scare up in the way of transportation. He found a school bus at the emergency-room entrance, its engine idling; orderlies, doctors, and nurses were helping men and women dressed in white hospital gowns and robes to board it. Polk saw the driver standing near the open front door.
“I got a priority passenger,” Polk said.
“We’ll make a spot for ’im,” the driver said.
Polk keyed his radio: “Davis, I got space, bring him out.”

Answer 3

Security Concerns

Dedicated Space

As mentioned by James McLeod, the word 'bus' is sometimes used as vernacular for an ambulance. While many patients were, indeed, evacuated on actual buses, it is likely that they were looking for an otherwise unused ambulance to keep Dent isolated from others during the evacuation for security reasons. Finding an ambulance would allow for that.

Guaranteed Space

In the alternative, they were simply looking for available space for this high-profile patient, in order to ensure nothing happened to him in the chaos of loading patients onto transport during the evacuation. Hence the attempt to radio back in that space had been found, and he could be brought out and loaded straight away.