127 Hours, the biographical survival drama about Aaron Ralston is as extreme an example as you can get without death. Ralston, who ended up amputating his own arm to free himself from a canyon he was trapped in for more than 5 days most certainly would have died if he had not been able to free himself. Why? Because no one knew where he went on his adventure or when he was expected to return. If you are heading out for a short 3 mile run or a 6 hour bike ride or run let someone know your planned route and approximately when you think you will return. It only takes two seconds and that way if something unfortunate happens and you are unable to help yourself, at least someone will know where to look and when to begin worrying.
Either the night before or the morning of my runs I tell Tani what my plan is. If I am running multiple roads and trails I may even leave a note. Below is what I left on our kitchen chalk board this morning.
Be safe out there. Peace