On my current department, it is SOP to not operate the apparatus any more than 10 mph over the posted limit. Regardless of the call. Whether it is a confirmed structure fire with occupants trapped, or a false alarm at the grocery store.
Of course, your rig (whether it's a Medic, Engine, or Brush truck) doesn't quite have the handling and power that a Crown Vic will. Ten over can be beyond the capabilities of some of those vehicles, especially on the interstate. Crown Vics are good well beyond legal speed limits in any part of the country.
As for this specific case, I think 115 or whatever speed he was actually going might have been excessive. But again, this is just opinion from someone not trained the way the S.O. was. I live in a large county with a small population that is spread out from one border to the other. It is not uncommon to see LEO's and EMS driving at what seems must be warp speed. From what I have been told from these guys, it is because the time frame to get from one end of the county to the other is so narrow. Whatever...that can be a whole different can of worms.
That was the point I was beginning to bring up earlier. Let's not lose sight of the original call - the Deputy was responding to an intruder in a house
. Like you said, a large rural county with low population density means the few law enforcement officers on duty need to get from one end of the county to the other, in no time.
When overtaking another vehicle while running code, you expect them to pull to the right and stop. At least, that's what they're supposed
to do. You realize that they may continue driving like oblivious dorks the same way you're going, too. You really don't expect they will slow to the right and then make a left-hand turn in front of your grill though. Let's not forget that the speed limit was 55mph in that section. The Jeep had to slow before making the left, and to the deputy that's the action you would expect to see when overtaking - the Jeep slowing. That gives him a chance to look at the rest of the roadway for obstructions and hazards.
As for the discussion that "it was 5:30pm so it was rush hour" or whatever that was...this happened in a rural county of 20,000 people, without a major population center nearby. Rush hour traffic jam most likely occurs when Farmer Joe moves his herd from the pasture to the barn, across the road. Welcome to the country.