Why Do Many Tractor Trailers Have a Large Plastic Barrier Running Below the Trailer?

Tractor trailers are a critical component of the transportation industry, responsible for the movement of goods across vast distances. However, one particular feature often seen on these vehicles, the large plastic barrier that runs below the trailer from the front wheels to the back wheels almost to the ground, serves a vital purpose in maintaining safety and improving efficiency. This feature, commonly referred to as a 'skirt,' has several functions, including aerodynamics, underrun protection, and preventing ice build-up.

Ice Build-Up Prevention

A key reason for the presence of skirts on tractor trailers is to prevent ice build-up under the trailer frame. When a semi-truck travels through wet or snowy conditions, the rear drive wheels can throw up snow or ice, which then starts to accumulate under the trailer. This can be particularly dangerous when the ice breaks off due to a dip in the road, creating large and hazardous chunks of ice in the lane of travel. These chunks can be a significant road hazard, leading to accidents and compromised safety for all drivers. The skirts deflect this snow and ice, preventing it from accumulating and maintaining safer conditions on the road.

Aerodynamics and Fuel Efficiency

Skirts also serve a crucial role in aerodynamics. By redirecting the airflow around the truck in a more efficient way, these skirts reduce fuel consumption. The principle is similar to that used in other high-off-the-ground vehicles like trucks and SUVs, which are now incorporating lower, more aerodynamic air dams. In the case of 18-wheelers, the need for clear airflow is even more pronounced due to their larger size. The materials used in these skirts are designed to be light and flexible, keeping weight down and reducing the risk of damage during transport.

Underrun Protection

While often associated with aerodynamics, some skirts also serve as underrun protection, especially in regions like the UK. Underrun protection is a safety feature designed to protect against collisions from vehicles driving beneath the trailer in case of a jackknife or loss of trailer control.

Regulatory Compliance and Fuel Cost Savings

Truckers operating in California must adhere to the state's "green laws," which mandates the use of skirts on tractor trailers. This is part of a broader strategy to reduce emissions and improve fuel efficiency. For fleet managers dealing with large numbers of trucks, even small improvements in fuel efficiency can lead to significant cost savings. By using skirts, fleet managers can reduce fuel consumption, which can translate into substantial financial benefits for the company.

Calculating Fuel Savings

The savings from using skirts are not always immediate or universal. In some cases, the benefits may not justify the investment if the trailer is primarily used at lower speeds or in terrain requiring ground clearance. However, for large-scale operations such as the fleet of Georgie’s Truck Emporium, the benefits can be substantial. Assuming each trailer saves 1% of fuel usage at speeds above 50mph, a fleet of 1,000 trucks can achieve significant savings. For a very optimistic figure of 8 miles per gallon (mpg) for the trucks, a fleet of 1,000 trailers can save up to 1,000 gallons of diesel for every 100,000 miles of combined mileage. Over a year, the savings for 1/3 of the trailers can result in a substantial bonus for the fleet manager.

Conclusion

In summary, the trailer skirts are essential for maintaining road safety, improving fuel efficiency, and complying with regulatory requirements. Understanding their functions and benefits can help both individual operators and large fleets make informed decisions about their use. Whether it's to prevent ice build-up, reduce fuel consumption, or adhere to safety regulations, the impact of these plastic barriers cannot be overstated.