Summer vacation has finally arrived for millions of families, and if you’re planning an out-of-town trip to visit relatives or see another part of the country, you’ll likely be hitting the road instead of flying.

Domestic airfares from June through August are 24 percent higher this year than they were in 2009, averaging $321 per round trip ticket, according to the fare-tracking website Bing Travel. The high cost is being blamed on the fact that airlines have cut back on the number of planes they fly, and fewer available seats means higher fares.

If you’ll be among the millions of people on America’s highways this summer, here are some unwritten rules of the road to keep in mind:

* Before setting out for your destination, review your car insurance coverage to make sure you are familiar with what you have. If you opted for just the minimum car insurance required in your state, you may not have adequate coverage if something goes wrong in a neighboring state. Log on to www.allstate.com/auto-insurance/state-coverages.aspx to quickly and easily check the requirements in the states you’ll be driving through.

* It’s also important to keep these driving safety tips in mind:

1. Let trucks pass. If you see a truck racing along as you’re attempting to merge onto the highway, let it pass you by. It takes the length of two football fields for a truck to stop dead in its tracks. Better to let a truck pass than to attempt a merge that could lead to disastrous results.

2. Take a break in bad weather. If it’s raining so hard you can’t see two feet in front of you, put on your hazard lights and exit the highway as soon as possible to wait the storm out.

3. Always be on the defensive and avoid distracted drivers. And most important – do not be one of those drivers. Refrain from using your cell phone or texting while behind the wheel, and if you come upon a driver with a cell phone to his ear, change lanes immediately.