I can't speak for Garmin, but we have put Tom-Tom's in all of our rigs (ambulance and fire). I have had several time that it tried to send me the wrong way. Specific addresses were up to 1/2 mile off. I found that they would get you to the street, but not necessarily the correct address. We have since updated the maps, but I lost confidence in them and went back to the old paper books. If you decide to go that way, I suggest that you get 1 as a sample and make sure they do what you want.
Well unless you have laptop computers mounted in your trucks then I donít see how this will work. Maybe you should invest in GPS systems, the good ones like TomTom, or Garmin. I think in Garmins it even gives you the option to set it to emergency vehicles. I have a TomTom and it gets me to a lot of places out in the county, even to roads I didnít even know existed, haha.