Overland, the journey to Belize by all weather roads takes 3 to 6 days from Texas, and 5 to 12 days from California. On entering Belize, motorists should bring along their driver's permit and certificate of registration. You need a Temporary Import Permit for your Car upon Crossing Mexican Border- get it from a Belizean Customs Official. You also need drivers license and certificate of auto registration to enter Belize. Third party or liability insurance is mandatory and can be purchased at the border. Driving is on the right. Sufficient funds for stay and onward travel also required.
If you want to drive from Cancun or other spots along the southeast coast of the Yucatan, The roads between Cancun and the Belize border are paved, two-lane all the way and quite easy to drive (at least as of two years ago). The distance is about 350 miles (583 kilometers) and I drove it in about 8 hours. You take highway 307 south from Cancun almost to Chetumal, then 186 into Chetumal or the Belize border cutoff. I would be leery of trying to cross the border with rental cars, though you can park them in Chetumal or Corozal if you are heading back the same way. There is no rental car return in Chetumal.
Once in Belize, holders of foreign driving licences are required to have a temporary driving permit which is obtained upon application to the Chief Licensing Officer in Belize City. The temporary permit is valid for 90 days. Holders of international driving licences are not required to obtain a temporary driving permit. No overnight parking in any public place is allowed.
Click here (http://AmbergrisCaye.com/pages/town/quickdrive.html) for one man's experience driving from the US to Belize through Mexico.
Driving yourself around Belize is a wonderful way to see the country. This gives you complete control in structuring your itinerary and the pace of your trip. For a growing number of tourists, this has become a part of their adventure.
Here are the main Belizean Highways:
The Northern Highway - Belize City to Corozal and the Mexican Border, Belize City/St Elena 93 miles- Paved, two-lane, in good condition. Driving time from Belize City to Mexican border: Approximately 2 hours.
The Western Highway - Belize City to San Ignacio and the Guatemalan Border, Belize City/Guatemalan Border 83 miles- Paved, two-lane, in excellent condition. Driving time to Belmopan: One hour, ten minutes. Driving time from Belize City to San Ignacio: 1 1/2 hours.
The Hummingbird Highway - Belmopan to Dangriga- The highway is two lane, paved, in excellent condition. There are several single-lane bridges which must be approached with caution. Traffic is usually very light. There is beautiful scenery along this route, and a couple of places to stop for a cold drink and a snack. Driving time from Belmopan to Dangriga: 1 1/2 hours.
The Southern Highway - Dangriga to Punta Gorda, Stann Creek Valley Road/ Punta Gorda 101 miles- A wide, fully graded, gravel road in generally good condition. This highway is a fairly straight route, with light traffic. It can be very dusty when dry, and slippery when wet with some sticky spots. Driving time from Dangriga to Placencia turn-off: 1 1/2 hours in dry season, remaining distance to Placencia is quite bumpy in spots: 30-45 minutes. Driving time from Dangriga to Punta Gorda: About 4 1/2 hours. Several contracts have been let for paving of the Southern Highway in sections. Some areas, beginning in Punta Gorda and working north, are already paved. Construction has begun along other points as well, and motorists should be cautious of crews and equipment.
Manatee Highway "The Coastal Road" - -This "shortcut" route between Belize City and Dangriga is an unpaved, graded, gravel road that starts at the Western Highway and meets the Hummingbird Highway about 13 miles west of Dangriga. It shaves at least 30 minutes off driving time between Belize City and southern points. Driving time from La Democracia (on Western Highway) to outlet at Hummingbird Highway: About 1 1/2 hours.
Since the country is only 185 miles from north to south and 69 miles wide, it's not a long way to anywhere! There are three principal highways: The Northern Highway, from Belize City north to Corozal and the Mexican border; The Western Highway, from Belize City west, passing by Belmopan, through San Ignacio, and on to Benque Viejo del Carmen and the Guatemalan Border; and the Hummingbird Highway, which starts near Belmopan and runs south to Dangriga. These are all paved. Additionally, there are the Southern Highway, from Dangriga to Punta Gorda, and the Manatee Highway, locally known as the "Coastal Road," which starts at La Democracia on the Western Highway (near the Belize Zoo) and also leads to Dangriga via Gales Point. The condition of all of these roads is described below.
Click here (http://AmbergrisCaye.com/pages/town/roads.html) for more detail on the roads and highways of Belize.
One must bear in mind that the rainy season, which is generally June through October, can have a great impact on the accessibility of some sites and areas. At that time, it is not advisable to venture too far off the main roads. Even during the dry season, a four wheel drive vehicle is often recommended, as the level of maintenance on the unpaved roads can vary. Most of the rental agencies in Belize only handle four wheel drives, and all have fairly comparable rates.
If you are planning on driving your own vehicle to Belize, you will be required to purchase insurance in Belize for the duration of your stay. The Belize Insurance Company office is located across the street from the Customs office in Santa Helena, at the northern border with Mexico. It is open every day except Sunday, when you must go to their office in Corozal (about 10 miles south). Be sure to check with the Mexican authorities prior to departure to find out about restrictions on private vehicles transiting through Mexico.
Notes on driving safety are the same as in most any country: Do not leave valuable items visible in the vehicle; keep the doors locked at all times; avoid driving the highways at night; fill your gas tank whenever possible; and do not pick up hitchhikers or stop to render assistance to people you do not know.
Although the roads have been significantly improved during the last few years, some are still pot-holed and can make driving for any distance very uncomfortable (especially the Southern Highway from Placencia down to Punta Gorda. Car hire is expensive and it is very important to check the small print in the insurance as most companies do not offer fully comprehensive cover. A four wheel drive vehicle booked through a reputable company is essential. If you are not happy changing wheels on an isolated road in the dark - think twice before considering this option. Most rental companies will not allow you to cross the border into Guatemala or Mexico, so ask before you rent.