I'm not sure how you're meant to 'respond' to a traffic stop. There could be further options for police calls to change although I'd also rather not have to be having a missions requirements change more than once. I'd suggest making further suggestions to particular calls as to what they can change.
Make sure you have the call expansion option on thought for this to work, found in the dispatch centre options.
Well it makes it more real. It not what's convenient, but it's what happens. A police officer could use a Taser on someone and then we have to call EMS etc.