Let’s get meta for a minute. You might usually think of truck chassis as one of the ways your goods move. But chassis are goods, too, and they have their own supply chain. When they’re imported to the US, they’re subject to tariffs and duties.

At Flexport, supply chain economists have a reasonable theory. Section 301 tariffs contribute to current truck chassis shortages in the US.

By extension, the shortage cuts potential trucking capacity and exacerbates the congestion pattern plaguing supply chains. Here’s why the idea carries weight.

Chassis Trade Flows

Principal Supply Chain Economist Chris Rogers has been tracking chassis trade flows. He’s found two telling changes.

First, the proportion of US imports of trailer and semi-trailer chassis from China has fallen sharply. The timing of a surge of imports in mid-2018 and subsequent decline lines up with the institution of Section 301 tariffs.

#tbt (Throwback Thursday) A lot has happened since Section 301 tariffs took effect in September 2018, so if you need context, we’re talking about the sweeping US program that added tariffs of up to 25% on certain Chinese imports. When they first kicked in, they rattled supply chains. As we see here, they’re still kicking.

Next, Rogers notes imports of chassis from Mexico have scaled up, rising by 190.3% in the past 12 months versus 2017. Mexican suppliers now account for 34.3% of chassis shipments into the US. This seems to indicate that chassis importers have shifted sourcing to Mexico due to a more favorable duty scenario.

At a higher level, Rogers sees a simple, yet largely unexamined chain of events: Section 301 tariffs disrupted trade flows of chassis, which caused a lag in their imports, which contributed to shortages at a time when the US severely needed them.

The shortage may have compounded congestion in ports by making it harder to get containers out of yards. The containers continue to stack up or stay on ships waiting at sea to unload, which then drives greater demand for more chassis in a feedback loop with grave consequences.

An Upturn in Imports

More recently, though, calculations show a marked recovery. Total chassis imports are up by 63.7% year-over-year in the three months to August 31 and by 14.0% compared to the same period of 2019.

The expansion rides on increased shipments from Mexico, shown in black. It’s also likely linked to fervent demand for logistics services in the US—chassis importers are highly motivated towards procurement.

Regardless, the outcome of the upturn is pretty straightforward for shippers: There still aren’t enough chassis to clear container yards.