@atoczf The explanation is simple... those 400 police stations generated over 1000 vehicles that had to enter the rest of the city. This they did and the long line dwindled away over time.
Not that it's important since once the landmark was unlocked, I demolished the police stations and thereby removed all of the new vehicles.

Not bad. Although I can't help noticing the traffic jam. Explaination Please! Thank you :)

Not something I thought about. But certainly an option.