What Are the Legally Permitted Dimensions of a Semi-Trailer?

Without semi-trailers, the world may be at a standstill. Because steel, fruits, vegetables, and daily necessities are all transported by semi-trailers.

For safety reasons, each country has different requirements for the dimensions of semi-trailers.

Country Length Width Height
United States
14M – 16.2M
United Kingdom
12M (kingpin to rear)
No legal height limit
18M (kingpin to rear)
12.5M - 16.15M
4M - 4.5M
South Africa
18.5M (Including tractor)

Among them, the US and Canada have basically the same requirements for the dimensions of semi-trailers. In other words, semi-trailers that meet US standards can transport goods in Canada. The legal semi-trailer dimensions in Finland are basically the same as other European countries.

Dimensions of a Semi-Trailer

Most of their semi-trailers are in accordance with the table standards, but some semi-trailers are special and have their own standards.

Flatbed trailer

Flatbed semi-trailers are designed to transport irregular and larger items, which usually cannot be placed in a dry van trailer. Flatbed trucks are most suitable for loading/unloading from the ground, not from the dock.

  • The law of the United States stipulates that the height of the flatbed semi-trailer shall not be higher than 60 inches (1.5M), and the height after loading the goods shall be lower than 108 inches (2.74M).

Lowboy trailer

Lowboy is commonly used to transport heavier, higher goods, such as tractors. It is characterized by an extremely low height in the middle, between 18 inches and 24 inches.

  • In the United States, the cargo height of low-bed trailers can reach 3.6M to 3.8M.
  • In the United Kingdom, the articulated vehicle, the semi-trailer of which is a low loader can reach 18M in length.

Goods over 102” (2.6M) are not prohibited to be transported but usually require special permits. Trailer manufacturers universally stick with maximum width guidelines, but in some cases, trailers can support wider loads, bulky items that reach well beyond the edges.

Oversized load and its special arrangement

The width of the cargo that exceeds the sides of the semi-trailer will be referred to as an oversized load. However, because some surface streets are narrower than highways, special permits are required even if the load is 102 inches.

In the United States, trailers exceeding the maximum width is subject to the following regulations:

  • Pilot/Escort – you’ll be required to possess a pilot vehicle, or maybe two, counting on the state and city in question, also as cargo breadth.
  • Law Enforcement – Some states require super loads to be escorted by enforcement vehicles or security personnel. Note that the hauling company is typically required to buy this service.
  • Signage – Both the pilot vehicle and your tractor-trailer will be got to have signage stating “oversized load” to warn other drivers.
  • Flags – Your trailer/load may have to be flagged, either on all four corners or only on areas that exceed the limit. These must be standard red or fluorescent orange flags, 18-inches square.

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