As you may have noticed, GTA IV's natural system for spawning police cars and officers is a little bugged. Primarily, it doesn't mix the two types (Skinny cops and Fat cops for peds, and the Vapid Cruiser and Merit Patrol for cars) it just goes all in with them. For many, this is annoying (to say the least) and kinda immersion breaking when 15 fat clones are all having heart attacks while Niko goes on a rampage. Some have tried to alleviate this problem by replacing fat cops with female officers, but the fact that you can't get a mixture has always bugged me. Here's an example:
How do we fix this?
Well, frankly, we can't, or at least not in the sense of getting the game to choose both models equally. But what we can do is simply stop the game from picking fat, unrealistic cops when deciding what officers should be spawned. It is also worth mentioning you can pick any police model, and also replace the officers in Alderney (or have state troopers spawn anywhere.) The best part? This takes about 15 seconds and only requires notepad.
Grand Theft Auto IVCommonData and open up pedgrp.dat
Press ctrl+f and search "# POPCYCLE_GROUP_COPS" or simply keep scrolling until you see it.
It more than likely looks like this:
# POPCYCLE_GROUP_COPS (M_Y_Cop_Traffic removed. Was the one in NJ)
M_Y_Cop = Skinny LCPD officers. Almost all mods mod this.
M_M_Fatcop = The two fat LCPD officers
M_Y_Strooper = The State Trooper Model
M_Y_Cop_Traffic = The blue shirted LCPD Traffic model
The game reads this as specific instructions. The first column is the first model that can spawn in all districts except Alderney. The second slot can also spawn there (but they will not spawn together). The final slot is the officer model that will only spawn in Alderney.
If it isn't apparent, you can simply change 'm_m_fatcop' to 'm_y_cop', and the game will always choose m_y_cop in Liberty City. You can change any of the 3 slots to any law enforcement model. I have m_y_cop spawning in all 3 districts.
This is a rare bug, but sometimes the game will freak out and pick all of the in game models flagged as police officers for checkpoints. The most obvious place this happens is the NOOSE/LCPD Station in northern Algonquin. This only happens to the models who stand around holding M4's, not the cops who stand around talking.
This is the same principal; tricking the game into only choosing one model.
Go to Grand Theft Auto IVCommonData
Open up cargrp.dat and scroll to # POPCYCLE_GROUP_COPS. The first two models on the list are the ones that spawn in traffic. NOOSE and SWAT Vehicles are handled on their own, so sorry, but you can't change that. If you change "police, police2" to "police, police, police2" then police2 will not show up in traffic. This is useful for those who cannot use the TBOGT and TLAD vehicle mod, or simply need another slot for a non-patrol vehicle. Alternatively you could add the NOOSE Cruiser or even FBI Vehicle, if that's your thing.