Nothing makes for a more unpleasant trip than having to go to the bathroom while driving down a deserted stretch of highway. Imagine how your pets must feel, cooped up in a carrier. If you're traveling with a dog, it's up to you to monitor its behavior and pull off for pit stops regularly. But with cats, things are slightly more complicated. Few people would allow their cats to hop out of the car and relieve themselves on the side of the road for fear that they might run away.
So what to do if you're driving across the country with a cat? Train it to walk on a leash? Unless you have plenty of time and patience at your disposal before your trip, you bring the bathroom with you. A portable litter tray folds up for easy storing, and you toss the contents after your cat uses it. This tray can also come in handy if you're staying over at someone's house or at a hotel with a cat.
Before you travel with your cats, remember that they're extremely territorial, habitual creatures. In addition to getting them acclimated to the motion of riding in a car, you should acquaint them with the new litter box in the weeks before your trip. That way, it will look and smell familiar, and your cat will be more willing to use it. Otherwise, you could end up with a stinky mess in the backseat or the hotel floor.