I recently noticed that the Burning substation call was modified by changing the requirements to 2 firetrucks instead of 3, as well as including patrol cars being needed. So i figured a few other calls could use a slight tweak to them as well.
First; Road accident. I found it a little odd that the road accident call only needed 1 firetruck and no patrol cars for traffic control / close a road if needed. So my suggestion is either modify it to require 1 police station and 1 patrol car or make a separate one with those additional requirements (like I've seen with Engine fire; one required 2 ARFF and one required 3) just for the sake of being realistic.
Second: Smoke investigation. This has the potential to confuse and maybe even make some new players worried. The mission requirements tab shows that a ladder truck and battalion chief are needed for the call. However, you first get the call when you have 2 fire stations, and you're not required to have a ladder truck until 3 fire stations and 6 fire stations for a Battalion Chief. While the call can be completed at this stage with only 1 fire truck,it'd probably be better for newer players to divide it into 3 different versions. First version would say only needs a firetruck at 2 fire stations, then the 2nd version; 1 fire truck 1 ladder at 3 stations, and 1 fire truck 1 ladder truck and 1 bat chief at 6.
Third: Trench Rescue. This is another modification for the sake of being realistic. Instead of being able to treat patients before the end of the call, it should be changed to be like the Stuck Climber call where patients won't be shown until the end of the call.