From my Guide to Mainland Belize:
A few travelers drive through Mexico to Belize. The trip from Brownsville, Texas, is about 1,225 miles and usually takes three to four days. Total non-stop driving time is around 28 hours. The fastest route from Brownsville/Matamoros is via Veracruz, Tampico and Villahermosa. You stay on Mexico national route 101 for about 118 miles, then route 180 or, for part of the way, 180D (a toll road) for 742 miles, then route 186 for 357 miles and then about 5 miles on route 307 to the Belize border. The toll roads are expensive, but you can make 70 mph on them, much faster than on the regular roads.
Driving through Mexican towns can be confusing, because roads are poorly signed. In general, avoid going through the town centers (Centro), as you can easily get lost and the hotels are more expensive.
To enter Mexico (and later, Belize) by car, you need your original vehicle title, and if your vehicle is not paid for, a notarized letter of permission from the lien holder. Besides paying the new Mexico tourist entry fee of 160 pesos (about US$17), which allows entry for up to six months, you have to provide a credit card in lieu of posting a cash bond to guarantee that you will bring the car back out of Mexico. By car, you are allowed only US$50 per person in merchandise to be carried into Mexico, plus as a resident of the U.S. or Canada you can bring in such items as binoculars, laptop computer, TV, camping equipment and fishing equipment.
If you are transporting goods of US$1,000 or more and are going through Mexico to Belize, you are supposed to use the services of a customs broker at the U.S.-Mexico border and get trans-migratory status, which costs money in fees and, many say, in bribes to Mexican federal officers along the way. It’s best just to enter Mexico as a tourist and not go the trans-mig route.
Mexican auto insurance is required; it costs from around US$50 for five days. Insurance for a month or two is not much more than for a few days.
For current road conditions in Mexico, call the Green Angels (if you speak Spanish), tel. 011-52-5-250-8221 from the United States or 91-5-250-8221 within Mexico. Except on toll roads, driving after dark in Mexico is not advised. You may be stopped frequently for inspections. As of mid-2000, gas in Mexico was about US$2.05 for regular unleaded (magna sin), US$2.25 a gallon for premium, and US$1.70 a gallon for diesel.
You should exchange enough U.S. dollars to get you through Mexico, as U.S. dollars are not widely accepted, or are accepted at a low rate of exchange. The exchange rate for U.S. dollars in mid-2000 was 9.25 pesos to the dollar, down from a high of around 10 pesos in 1999. Gasoline stations in Mexico usually do not accept credit cards.
Sanborn’s (tel. 800-222-0158, e-mail firstname.lastname@example.org; www.sanbornsinsurance.com)
is a good source of information on travel in Mexico and for Mexican auto insurance. A Web site with all types of helpful information on Mexico is www.mexconnect.com.
On arrival at the Mexico-Belize border, you again need your original title (no photocopies) for your vehicle, or, if you do not own it free and clear, a notarized statement from the lien holder that you have permission to take the car out of the U.S. You also have to buy Belize auto insurance. There are brokers at the border. Three months of insurance should cost about US$50 to $60, or one month about US$30. Crossing the border you may have to have your car sprayed to kill hitchhiking bugs — the fee is around US$4.50.
If you plan to stay in Belize and keep your vehicle there, and do not have an exemption, you have to pay import duty. The rate varies by number of cylinders and type of vehicle, but it runs about 45 to 75% of value, including sales tax and other add-ons. Pick-up trucks (not SUVs) are taxed at 10% duty, plus tax. If you are just visiting, you should not have to pay the import tax, but the car is entered on your passport so you cannot sell it in Belize. There are customs brokers at the border to assist you with your paperwork. They’re worth the small fee — perhaps US$20 to $50 — they typically charge.
TIP: Avoid border crossings on Mondays, the busiest day.