Not that I have actually noticed, as I live in the Northern US, and see quite a bit of both 2 and 3 axle semis and 1 or 2 axle trailers. The main thing to consider -- and this would be my best guess - is that it all has to do with the roads. It is possible to manufacture an axle to support the entire weight of a semi, but the main problem is that roads are only designed to carry a certain amount of load, thus is why they create trucks with more axles. Do they build roads differently in the South? Yes. In Northern States, roads are built to withstand, not only normal use, but also they have to be designed with the changing winter/summer climate that includes almost always a freezing/thaw cycle, which you don't have in the South. Because of this, roads in the north are designed to be resurfaced/repaved more frequently. The economics of this dictates that they not use as much material because no matter what, the expansion and contraction of the road surface will need it to be maintained more often. Because of this, the governments must dictate more stringent rules on axle weights for all commercial vehicles. The idea is to distribute the load over a greater area so as to not damage the road as much. Almost all national freight carriers in my area have tandem axled trucks and trailers. Most of the interstate carriers do as well, and the only ones who do not necessarily have multi axled equipment are local haulers, who usually do not haul a full load. For more detailed information, try contacting your states department of transportation on road design and climates.

It is to do with the weight and wheather/road condtions becuse in th north you have snow ice so you need more traction to stop in time but if your on snow you loose alot of the traction espacliy when it is cold the rubber on the tire does not flex as much. Roads becus of weather and roads becuse if you are driving on the cement that is warm usllay it wil given you more traction but if it is cold less taction . And usllay trucks carry heavy loads in the north because that is were there is haeyloads such as wood beer and etc plus the pouplatin has a afect to it becus most of north amerca has the most puoplatin desinty near newyork to area and abit so the truck compaies dont need as much thing which means less weight All of these factors is way north has more axels on trucks

By "north" specifically in Michigan, it is because Henry Ford fought and won for the right to increase the weight of the shipments of steel that was needed in his factories. In order to support the extra weight there needed to be more axles. The gross weight limit allowed on the Michigan Interstate system without the need for special permits is 154,000 Lbs on an 11 axle tractor/trailer combination. These "Michigan Rigs" are also allowed in the northern most sections of both, Ohio and Indiana, within one mile of the Michigan border. Trucks of this weight entering Ohio and Indiana must be a "combination" trailer of two. The driver must disconnect the last trailer and proceed with the front trailer to make his/her delivery. Then, the driver must return with the empty trailer and exchange it with the second trailer to make the final delivery. In Michigan, however, none of that is necessary. Although 154,000 Lbs Gross Vehicle Weight does sound like a lot. There is less weight per square inch of tire-surface upon the road surface than the 18-wheel configuration with a gross vehicle weight of 80,000 Lbs. Henry Ford won, but the law has never been reversed or changed since.

The primary reason for this is because of the potential for damage to the roadways in the spring by heavy truck traffic. The ground freezes in winter to a depth of two to four feet. As it thaws in the spring, the ground is quite soft, even under well-built major roads. Many secondary and tertiary roads have a lower per axle weight rating in the spring to help reduce road damage from heavy trucks. The trucks either have to reduce the weight of their cargo, affecting their profitability, or use as many axles as economically feasible to lower the weight per axle. Many trucks have a third, drop-down axle on the trailer to help in this regard. They may also need to drop the third axle if they are running heavy loads at any time of the year.

Something else to consider, is the bridge law. Where a vehicle has to have the weight distributed to cross a bridge due to the bridges structure. In certain states it especially important to have length when crossing bridges, which would mean more axles for the amount of weight carried, to evenly distribute the weight.

Trucks with 2 axles and 6 tires or at least 3 axles are to follow the truck routes in Section 4-13 of the New York City Traffic Rules. Trucks going through a borough without stopping over must use the through truck routes. Local truck routes are for trucks with origins, stops or destinations in a borough. See also the Truck Route Maps. http://www.i80equipment.com/tree-trucks.shtml