In your 'vehicles.meta', each vehicle as 2 specific lines for it :
For information, it seems like the maximum limit is '1.000'.
For your traffic problem, you could try finding a mod that changes the neutral AI driving behaviour.
adding 'FLAG_LAW_ENFORCEMENT' in the desired motorcycle makes your game crash ?
I remember REDUX dispatch was already including a motorcycle, and I've never saw one.
I'd assume that motorcycle vehicles are binded to a specific dispatch type, and I suppose 'DT_PoliceRiders'.
I've never tried to dispatch motorcycles in game tho !
I would say try ?
I'm interested by the answer too.
I'm working a new fresh modded install of my GTA, so i'm making my dispatch while answering. Note that there is a LOT to know about the dispatch. I'll advice you to go check my profil posts, as I was in your case weeks ago. There are a lot of tricks 
<WantedLevel3> ---------------------------------------------------------------------------------------------------------} The Wanted level, obviously.
<DispatchServices>
<Item>
<DispatchType>DT_PoliceAutomobile</DispatchType> ---------} The dispatch type. Note that some cars/peds can only be dispatched on certain types of 'DispatchType'.
<NumPedsToSpawn value="8"/> -------------------------------------} The number of peds for that 'DispatchType' that are gonna be spawned. 8 = 4 vehicles of 2 people each in 'DT_PoliceAutomobile'.
<DispatchVehicleSets>
<Dispatch>POLICE_CAR</Dispatch> --------------------} Related earlier in the Dispatch.meta file as 'VehicleSets'.
<Dispatch>POL_SHER_INTERV</Dispatch> ---------} As you can see i've made mine.
</DispatchVehicleSets>
</Item>
</DispatchServices>
</WantedLevel3>
Here is my created 'POL_SHER_INTERV' with modded peds and cars.
<Vehicle>
<Name>POL_SHER_INTERV</Name>
<ConditionalVehicleSets>
<Item>
<ZoneType>VEHICLE_RESPONSE_ARMY_BASE</ZoneType> ---------------} Army Base
<VehicleModels>
<Vehicle>crusader</Vehicle>
</VehicleModels>
<PedModels>
<Ped>S_M_M_Marine_01</Ped>
</PedModels>
</Item>
<Item>
<ZoneType>VEHICLE_RESPONSE_COUNTRYSIDE</ZoneType> -------------} Blaine County
<VehicleModels>
<Vehicle>shersand</Vehicle>
</VehicleModels>
<PedModels>
<Ped>s_m_y_sherswat_01</Ped>
</PedModels>
</Item>
<Item> ----------------------------------------------------------------} Los Santos from here to end
<VehicleModels>
<Vehicle>PIN</Vehicle>
<Vehicle>polred5</Vehicle>
<Vehicle>polguard</Vehicle>
</VehicleModels>
<PedModels>
<Ped>s_m_y_polswat_01</Ped>
</PedModels>
</Item>
</ConditionalVehicleSets>
</Vehicle>
@Aurora11 said in Changing number of police vehicles to respond:
let's say if you change the number of peds to spawn in police1 at the vehicles.meta, like 4 cops for example, then <NumPedsToSpawn value="4"/> probably will spawn 1 police car with 4 cops in it.
Actually this isn't entirely true. In most 'DispatchType' it's only x2 peds for one vehicle, with some few exceptions, for example the fbi2 vehicle (which, btw, only works as intended in 'DT_SwatAutomobile').
But I really advise you to go check my posts, there is nearly all you need to know, thanks to some amazing modders !
@ItsJustCurtis said in Increased traffic variety:
Reinstalled VWE
Looks like this was the thing that messed it up. I don't see why it could've crash without it.
Sorry to hear that !
I don't know how much of a difference in traffic editing the vehicles.meta did, but sometimes we are so into our things that we see huge difference in little details when they are none.. I just hope it was really the case for you !
Now you are telling me that this fixed the problem of spawning variation, need to figure out why it reduced traffic now.
@ItsJustCurtis What happened, and when ?
@ItsJustCurtis I guess your are talking mostly to regroup the add on vehicles in the same 'vehicles.meta' ?
I've never tried it but it could be a good idea.
The way I see it, is copying each addons 'vehicles.meta' into the main one. But seems like a lot of these files are hard limited by memory or something like this. When they are overloaded, strange bugs seem to happen.
Edit : Need to take into account that, I think, addons files (dlcpacks)have priority over the main files.
I wouldnt take the risk my self to do all that work for nothing !
@Aurora11 Im on my phone right now so I can't go in details.
Everything you want to know is in 'dispatch.meta'.
That file is related to how the law enforcement is dispatched when you are wanted.
Which vehicle/ped, how many, for each wanted levels.
Check the wanted levels at the end of the file, and which group names are dispatched at each level. Then you can find the group names earlier in the file.
@ItsJustCurtis I've read somewhere that this is happening since GTA IV.
I've had the same problem, it looks like after some point the game just can't handle the spawn variety, and kinda bug.
I found a fix, partial in my case because i've never took the time to do it entirely, so I don't know if it works completly.
I realised that the repeating spawning cars are always the ones with huge 'maxNum' values (in 'vehicles.meta') : 999, 50, 100...
Just for the sake of information, that line represents the maximum amout of cars that can be spawned in a cycle.
So i've edited this value for some of them to what I consider a reasonable amout, which is about 3 to 6.
The thing is, if you want this as a permanent fix, you need to do this with all the cars from your 'popgroups.ymt'.
The only parameter that you need to take care of, is that some cars probably needs higher values for scenarios/missions, and I have no idea about that.
Anyways, hope it could help.