Yes, believe it or not there are rules of the road while driving in Mexico.

If you can read Spanish, here are some FAQs regarding the laws applicable to the federal district (Mexico City). Each Mexican State will have similar laws.
http://www.setravi.df.gob.mx/p_frecu...q.html?tema=32

Some of the thing I learned while reading through the FAQs that visitors driving in Mexico should be aware of include:

Children under age 5 may not ride in the front seat (Fine is at least 10 days current minimum wage).

Seat belt use is mandatory (Fine is at least 10 days current minimum wage).

Running a red light or stop sign is a minimum fine of 5 days minimum wage.

No person may drive a vehicle on a public highway or street if the person has a blood alcohol level of greater than .8 grams/liter or a breathalyzer reading greater than .4 miligrams per liter. Mandatory jail time of 20 to 36 hours for violating this law plus impounding of the vehicle.