This might seem kind of obvious to some, but I just wanted to point it out in case people hadn't caught on to it on their own. When playing by yourself, you can always use the vehicle stations to deploy 2 vehicles. Every time I spawn vehicles, I almost always spawn both, and then go on my way with one of them to complete quests. Once you've done what you need to do, you can find another vehicle station close to you, and use your second vehicle as a fast travel point essentially.
This technique is especially useful when different quest chains have you traveling multiple times across a large landmass. By deploying to your different vehicles you can make up the ground very quickly. This is also a big help in the timed fetch quests. You can just park a vehicle in a desired location, and once you start the quest just hit up a vehicle station and deploy to the car you left.