The traffic in Empire Bay is surprisingly dense, but it's scripted to be sparse in certain story missions to save memory. By altering the spawning scripts:
User-created Lua scripts for Mafia II generally fall into three categories: mafia 2 lua scripts
Legitimate mods that rebalance or expand the game using Lua: The traffic in Empire Bay is surprisingly dense,
Filename: nopolice.lua
Function: Sets the cop wanted system to zero permanently. You can kill civilians, steal cars, and run red lights with impunity.
Note: This breaks scripted missions where police chases are mandatory (e.g., "The Wild Ones"). "The Wild Ones").