I've traveled in Mexico a bit. I've seen 4 cars pass 10 on a two lane road (highway) in the daytime. Nights are crazier. Seriously... don't drive at night. Many trucks will turn on their left blinker to signal you to pass them but they do miscalculate sometimes. "Topes" is Spanish for speed mountain, on the actual highway. If you go for this, there is a good chance that something scary will happen during your trip. Above all else, keep you cool.