Plan ahead in case there is a problem. It's a good idea to determine your route, and if you are going a long distance, map out some veterinarians along your way. Keep their phone numbers handy in case of emergency. (Remember, you can't dial 911 and ask for a veterinarian.) Other phone numbers you should keep readily available are those of your emergency contact person as well as friends that may be able to help with the horses. Make sure that these numbers are stored in your phone as ICE (In Case of Emergency) so emergency personnel know who to contact. Since phones can easily become separated from you in an accident, another option is RoadID, a velcro band that allows for up to 6 lines of personalized text. It was designed for bikers, but can be useful in any situation that you may not be able to communicate effectively.
Also keep in mind, if your vehicle becomes disabled for any reason, and you need a tow, wreckers will not haul you with a trailer attached, and are not allowed to even touch the trailer in some states. Plan accordingly - have a few numbers of friends in the area who would be willing and able to "pick-up" your trailer and continue on to a safe place for your horses.
It can be a dangerous road out there, but with a few precautions and some time spent planning, you can avoid many serious crises. If you would like to read more about safe trailering, check out these tips as well. Other equine emergency information can be found at our friends over at The Horse.