Any wheeled vehicle is by tradition a reflection of us and how we handle life. Carts, chariots and carriages tend to have a more old-fashioned resonance, whereas a car is more up to date and in keeping with modern thinking.
All such vehicles reflect the physical body, so anything wrong with the vehicle may alert us to a problem.
A car in particular is a reflection of a person’s self-image and possibly sexuality and indeed any part of a car has significance.
The back tyres might suggest our support system, the steering wheel the way we control our lives and so on.
If the brakes are not working we are not exercising proper control over our lives.
Too many people in the car would suggest that we feel overloaded by responsibility.
Also consult the entries for car, carriage / cart / chariot, passenger and wheel for additional information.