Formal:
* Fleet: This is the most common and formal choice, especially for large groups of cars used for commercial purposes or transportation.
* Convoy: This refers to a group of vehicles traveling together, often for safety or military reasons.
* Train: This is less common, but can be used for a line of cars moving in a single direction, like a traffic jam.
Informal:
* Bunch: This is a casual and informal way to refer to a group of cars.
* Lineup: This is used for a group of cars displayed together, like at a car show.
* Park: This can be used for a group of cars parked together, like in a parking lot.
* Garage: This can be used for a group of cars owned by one person.
The best collective noun to use will depend on the specific context and the tone you're aiming for.