Another aspect of this analogy that resonates with me is the idea that there are going to be people that come into your life and parallel your course for a while. Those who you date, learn something from, gain insight with, often end up going in different directions. There is value in going in the same direction with someone for a time, even if you don't end up in the same ultimate destination.
NRE can be a lot like drag racing. You're driving style can get a bit nuts while you hurry to keep up with someone driving something flashy and loud. The person that pulls you ahead of the rest of your partners too far, or takes you off course, isn't going to be the best option in the long term. Listening to input of that nature from your existing partner(s) while in the midst of NRE would be advisable.
Tail gating is just as annoying in a personal realm as it is on the road. Let's say you have a partner that is on your tail all the time, urging you to speed up, to exceed your safety limit so that they can move faster. Do you slam on the brakes? Urge them to pass you by? Give them the finger and slow down even more? Remember that often those that pass others by on the road find themselves sitting at the next stoplight right next to the slow-but-steady drivers, having gained nothing but the ire of their fellow motorists!
Some of us like the scenic route, and others prefer to take the most direct route available to a given destination. Examining that stylistic difference, as it relates to relationship processing styles, is a very worthwhile perspective to have!
Sunday drivers who putter along enjoying the scenery are likely to be a bit frustrating to those who get car sick on winding roads, and would just like to make it to the next rest stop. Similarly, people who like to emotionally drive "straight on through" are going to have a tough time convincing those who prefer a set limit on "miles per day traveled", that it's a great idea to move straight from monogamy to live-in polyamory without exploring many interim stages. Sure, you'll eventually get to Florida, but you'll stink, be tired, and disinterested in spending time together when you get there!
Bad weather counts! There are times where what is going on inside the vehicle is pretty secondary to the wind, rain, snow and sleet, of outside events. Recognize that there are times where moving a relationship forward at full speed isn't safely possible due to outside events. If someone has just had a baby, gotten a divorce, changed jobs, moved, had a significant illness, etc., this is a good time to move at the slowest comfortable pace, until conditions improve. The really nifty thing about moving more deliberately for a while is that, when the pace picks up, it often feels like you are making amazing progress by going the "speed limit"!