Make sure your registration and driver's license are valid. Your vehicle can be impounded if these are not current.
Purchase Mexican insurance.
Make two copies of your Mexican insurance certificate; one to keep on your person and one to keep in the vehicle.
Make a copy of your vehicle registration and keep the copy in your vehicle and the original on your person. In case the vehicle is stolen, it will facilitate proving ownership.

Driving & Safety Tips:

Traffic violation laws vary from state to state.
Speed limits are stated in kilometers (1 mile = 1.6 kilometers).
Yellow lights are a signal to stop, not just to slow down.
You can get a citation fine for taking a right on red traffic light although you will see many drivers doing it anyway.
In many cases, the "fast lane" is a passing lane only. You should move back over into the slow lane once you pass someone.
Lanes can merge much quicker (with not much time to merge).
Construction areas can come upon you suddenly with little warning.
Using a cell phone while driving is a traffic violation.
Watch for cross walks, in many areas pedestrians have the right-of-way.
Driving boundaries or "comfort zones" are smaller, people will drive closer.
Take notice of the vehicle's brake lights in front of you, many times they do not work.
Vigilance of the roads is necessary to avoid animals, people, and other obstacles.
It is wise to avoid driving at night.

Crossing the Border:

Before you cross the border, be vigilant of the signs telling you where the declaration lanes are if you need to declare anything to the Mexican customs officials. If you need a vehicle permit or a tourist card, you may drive thru this lane as well, park, and obtain those documents.

If you don't need to declare anything, you may cross in any lane that says "Nothing to Declare" (Nada que Declarar). But this doesn't mean that you won't be questioned or searched by customs officials. When you cross, you will see a traffic light with a red and a green light. A red means you have been selected for secondary inspection and a green means continue on your way unless an official tells you otherwise. If you are selected for secondary inspection, you must pull over into the customs facility. There, they will conduct for the most part, a quick search unless they find something that should have been declared. Usually they check the trunk and take a glance inside the vehicle.

Toll Roads and the Green Angels:

The green angels are mobile mechanics who patrol the Mexican toll roads in green trucks to offer free assistance in the case of a breakdown (labor and towing are free, but to replace a part would be at the expense of the car owner). In addition, they are equipped to give tourist information as they are connected to government offices via a network. Although their services are free, tips are appreciated. Take notice of the emergency signs along the road with phone numbers. If your vehicle breaks down, pull over to the side of the road and lift the hood to signal them. Call one of the numbers below depending upon which toll road you are on and the green angels are on their way to help. The extensive network of toll roads is country wide. To view a map of the routes that are patrolled by the green angels, go to this link. (Spanish only)

Military Checkpoints:

Military checkpoints are set up along certain roads and highways. As you approach the checkpoint you will see several young men dressed in army green uniforms with guns. Some tourists do get nervous at this sight, but their purpose is to find drugs and illegally imported items being transported. At some checkpoints you may even see a sign posted by the government for tourists so they feel more secure about the process. Be sure to slow down or stop if you are asked. They may ask you a couple of questions (although not in English) to find out where you are going (¿Adónde van?) and where you have been (¿De dónde vienen?). They may ask to do a routine check of your vehicle. Cooperation is key for a smooth exit.

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