Every sim in my town uses taxis, and I'm sure that I could go through and add a car to each individual lot, but is there a mod that could do that for me?

Even if you gave every sim in the city a car, they will still randomly use taxis. And I am unaware of any mod that provides cars to your sims automatically. There is a function in NRaas SP that will allow an inactive sim to purchase a car if they meet a certain threshold of family funds, but it will not simply push vehicles out onto every inhabited lot.

Nraas's Traffic mod lets you set it where a taxi is not used in normal sim routing.

as above - Nraas Traffic (for general rules like taxis, ice trucks limos) and Retuner for changing behaviors more specifically (did I made another silly word? >.>)

There was an issue about cars creating lag in worlds at some point, so it was recommended not to add cars on lots, nraas should probably fix it though. At least I know of a clean up operation of stray cars around, may have been StoryProgression.

NRaas SP creates cars for NPC sims - it's based of "net" income and some option within SP settings/tunings handle this (however I don't know which one). Also game creates taxis for "city" towns - particulary for each show/bar/disco or whatever lot. This is obviously great lag generator like limos and trucks are the cherry of the top of this.

Hey guys, you will get more timely (and sorry, occasionally more accurate) answers to some of these NRaas mod questions if you post them on our site. It's kind of what we are there for.

The delta setting in the NRaas Traffic mod only controls the "fake" taxis that roam around for the streets for ambiance. They don't have drivers and no sim can use those for anything. Setting the delta to a highly negative number (-500 should shut that engine down completely for most worlds) does not affect whether sims take "real" taxis to get around. Setting the delta to zero would have no effect at all. Also, the settings are world specific, so what you have going on in Bridgeport does not affect what you have set in China (Barnacle Bay, Dragon Valley, etc.if you use Traveler) within the same game save, although when traveling to a world for the first time within a game, by default that world will inherit mod settings from the place you started. They are still independent settings, though.

There is also a setting in that mod to switch off the game's ingenious (coughs) issuing of temporary cars to inactives who lack them so they can get around. Invariably those are cheap, awful looking cars that the inactives abandon after a single trip and need to get cleaned up via Overwatch or things get clogged up. Frankly, I would rather see an occasional taxi in a world where there shouldn't be many if an inactive sim is actually using it to go someplace than have the abandoned cars thing happening.

Got a similar problem - sometimes, ALL NPCs drive either a Sloppy Jalopy or Big Lemon. This happened before I used CC.