A chassis is the wheeled steel frame a shipping container sits on while it travels by road. The container is the box. The chassis is the trailer underneath it. They are almost always owned by different companies, rented separately, and billed separately — and that split is where importers lose days they never budgeted for.

Why the container and the trailer are separate

Domestic freight moves in a dry van, where the box and the wheels are one unit. Ocean freight cannot work that way. A container has to stack twelve high on a ship and ride a rail car with no wheels at all, so the wheels are a separate piece of equipment that gets attached at the port and taken off at the destination.

That means a truck arriving at the terminal to collect your container needs a chassis under it before the crane will load anything. No chassis, no move — and the terminal will not lend you one out of kindness.

Where chassis come from

Three arrangements exist at the Ports of Seattle and Tacoma, and the difference matters to your bill:

  • Pool chassis — a shared fleet managed by a pool operator. The trucker pulls one from the pool, uses it, and returns it. Billed per day.
  • Carrier-provided — the ocean line supplies the chassis with the container, usually bundled into a set number of free days.
  • Carrier-owned — the drayage company owns its own chassis. No pool rental, no availability roulette, but the trucking company carries the asset cost.

Most importers never see this choice. It sits inside the drayage rate as a line item called "chassis" and quietly runs at a daily rate for as long as the box is out of the terminal.

The chassis split — the expensive one

A chassis split is what happens when the chassis is not at the terminal where the container is. The driver arrives, the box is ready, and there is no equipment to put it on. He then has to drive to a separate depot, collect a chassis, and come back.

That is not a small inconvenience. It is typically an extra two to four hours of driver time, it burns an appointment slot, and on a bad day it costs the entire move. If the return trip misses the terminal cut-off, the container sits another night — and if you were already close to your Last Free Day, that night is the one that starts demurrage.

Splits are worst in peak season, when pool inventory runs thin, and they are almost invisible in advance. This is one of the reasons a drayage company running its own chassis behaves differently from one that does not: it is not waiting in a pool queue.

Chassis types you will actually see

  • 20ft — for a single 20-foot container.
  • 40ft — the standard workhorse.
  • Extendable (combo) — slides to carry 20, 40 or 45 foot boxes. Flexible, so pools like them.
  • Tri-axle — three axles instead of two, to spread weight. Required for heavy loads in states with tighter axle limits.
  • Gooseneck (drop frame) — the front section sits lower so a high-cube container clears the legal height limit.

That last one catches people. A 40-foot high cube is a foot taller than a standard box. On the wrong chassis, the loaded height goes over 13 feet 6 inches and the move is illegal before it leaves the gate.

What chassis cost you, in days rather than dollars

The daily rental is rarely the real expense. The real expense is what the chassis does to your clock:

  • You are paying chassis rent for every day the loaded box sits in your yard waiting on a dock door.
  • You are paying it again for every day the empty sits after you have stripped it.
  • And the same days usually carry per-diem on the container itself, because you are holding the carrier's box too.

Two meters, one delay. Run the numbers on your own container with our demurrage and per-diem calculator.

How to keep chassis from costing you

Very little of this is in an importer's direct control, which is exactly why it should be in the contract rather than left to chance:

  • Ask who supplies the chassis before you book drayage, not after a split has already cost you a day.
  • Strip the box fast. The single biggest chassis saving is not renting it for a week. Transloading at the dock puts the container back the same day.
  • Watch high cubes. Confirm the gooseneck before the truck is dispatched, not at the gate.
  • Keep drayage and the warehouse together. When one party controls the pull, the yard and the dock door, there is nobody to blame for the chassis sitting loaded overnight.

We run drayage into our own Kent facility, minutes from both ports, which is the short version of all of the above: the box comes off the chassis the day it arrives.