听力原文： This is Jim Johnson with Travel Talk. It's summer and it's vacation time. For some people this means long hours in the car and on the highway. Here are some tips to help you stay safe while on the road. First, the Do's. If you're traveling with more than one driver, try to switch drivers occasionally so that you don't spend too much time behind the wheel. Remember to stop frequently and take a break. Make sure you know the signs of drowsiness: missing road signs, difficulty focusing, and yawning. Now the Don't's. Don't count on distractions such as the radio or an open window to keep you awake. And even though a cup of coffee might give you a lift, remember that the effects of caffeine wear off after a short time. Finally, don't drive between midnight and morning. Tune in again tomorrow when we'll talk about vacation destinations that both adults and children will enjoy. What is the main topic of the talk?