Get your vehicle serviced by a reputable mechanic. You'll rest easier knowing that your engine and brakes have been given the once over. If you're still worried about your car standing up to the rigors of a road trip, rent a car or join the American Automobile Association for the emergency roadside service.
Keep emergency supplies in your car-water, food, blanket, flashlight-in case you find yourself stranded. Don't forget auto supplies as well, including jumper cables, a jack and flares.
Move past any fears of traveling alone by having a plan for possible worst case scenarios. Bring your cell phone and emergency phone numbers along on your trip. Learn how to change a flat tire. Confront fears with an action plan.
Study maps. While a mapping program like Mapquest is great for showing you how to get from here to there, the old-fashioned foldable road map can show you what else is out there.
Be open to unscheduled stops. Your schedule is your own when traveling alone, so stop at that scenic overlook or visit a quaint antique store that catches your eye for as long as you want.
Leave safety notes in your glove compartment if you plan on hiking or just being away from your car for several hours. A safety note provides information about where you went and with whom. Safety notes help law enforcement locate you in the unlikely event that you don't return when you're supposed to.
Decide whether you want to have hotel reservation or just want to wing it. While spontaneously deciding when to stop and where to stay is appealing, so is having a room already lined up at the end of a long day.