Analogies should only be used like trains: An efficient, well thought out path from point A to B on a vehicle that is piloted by a pro. Car analogies look appealing -- they look more flexible, but this can also lead to people taking overly circuitous routes to get to the point... maybe the driver just doesn't know what they are doing, maybe the road system is poorly optimized because it needs to hit lots of points, or maybe the driver is like a sneaky cab driver that intentionally takes an inefficient path to increase the fare.
The wider availability also leads to a situation where cars are mostly piloted by random people with no particular qualifications other than a basic license. This can result in lots of car crashes. Of course, it is also possible for a train to get derailed, but this is a rare occurrence. On the other hand a derailing can result in more damage... ah... hmm, I forget where I was going with this...
