Driving in Mexico at night should be avoided at all costs. Most roads are poorly lit and sometimes large animals such as cows and horses wander onto the roads and are impossible to see in the dark.
I used to recommend that if a person must drive at night, they make sure to take the toll-ways (cuotas) since they are closed off and generally much better lit. That was until a friend told me his story.
My friend was on his way home from a trip to Manzanillo on the tollway. He was driving in the morning while it was still dark, doing about 60 mph. According to him, the last thing he remembered was the eye of a big black cow. He bulldozed into this huge beast at 60 mph.
After he regained consciousness, and realized that he had only suffered minor injuries (his car was totaled, though), he and the police officer that had arrived on the scene went over to take a look at the cow he had smashed into.
Around the cows neck; barbed wire.