Something bizarre I have noticed in relation to the use (or lack/the overuse) of police cars for missions - particularly those involving fire trucks. 
Large fires like the recent scrapyard fire, or the commercial fire - these both require police cars to attend. Whereas missions like the gas station fire or dangerous goods truck accident lack such need for police cars. One would think you would require police cars to block off nearby roads (particularly for large fires resulting in high risk of public danger), but the game does not incorporate this for particular missions... Or simple missions like a road accident or vehicle fire in tunnel - often these still need a police car to help manage traffic etc. Yet that does not occur.
So my question is... Yes players want access to large missions resulting in substantial pay, but why have police cars at some missions and not others where they would typically be required? 
In saying that though - a large volume of players appear to avoid having police in their game altogether. This may be due to a number of reasons, but perhaps there could be a setting that says something like 'involve police in missions' - meaning yes or no to missions like the commercial fire to require police cars, based on if the player wishes to have that service in their world.
My overall thoughts are that this should definitely be looked at, but what do others think? Comment below!
