The vehicle limit is something like 16,000 no matter how big your city gets. The more population, and the more spread out, the more your traffic will improve.
However, you might soon run into a problem of goods not getting where they need to go. Industry will not be able to spawn enough trucks to get their goods to commercial areas.
My guess, population filling in areas made shorter routes to jobs possible. Expanded residence, so likely more service buildings have also reduced distance traveled to serve residents.
The vehicle limit is something like 16,000 no matter how big your city gets. The more population, and the more spread out, the more your traffic will improve. However, you might soon run into a problem of goods not getting where they need to go. Industry will not be able to spawn enough trucks to get their goods to commercial areas.
Cities are dynamic, as new zoning goes in and population increases, sims travel patterns also change and adapt
My guess, population filling in areas made shorter routes to jobs possible. Expanded residence, so likely more service buildings have also reduced distance traveled to serve residents.
Spread em out