WASHINGTON - If freight trains rumbling across the great American plains are the sinews of the supply chain in the biggest market on the planet, then trucks are its life blood.

Normally, an estimated 3.5 million truckers driving 16- and 18-wheel behemoths stitch together America's supply chain, a complex web from ports to warehouses to chain stores.

But trucking does not pay enough to compensate for the long hours at the wheel across this vast country. Add the Covid-19 pandemic to the mix, and the plethora of factors has contributed to a shortage of roughly 80,000 truck drivers - up from 61,000 in 2018 - industry analysts say.

This holiday season, the problems are hitting home.

A drop in the number of truck drivers willing to wait around at inefficient ports to ferry goods and sometimes drive for 18 hours a day, means that Americans, the world's greatest consumers, are finding it hard to get what they want.

The supply chain is fraying and that, in turn, is triggering another politically loaded problem - inflation.

The issue is serious enough to demand President Joe Biden's close attention. Last week, he said that he was initiating a three-month Port Action Plan to invest in American ports and relieve bottlenecks. He hosted a roundtable with leading retailers on Monday and, two days later, reassured Americans: "We're heading into a holiday season in very strong shape."

He added: "We averted a potential crisis by figuring out what needed to get fixed and then we brought people together to do the hard work of fixing it."

Congestion at ports is part of the problem. "Some people get paid by how many loads they do but if you don't get a load, you just sit and then you get paid for one little load," 24-year-old truck driver "Chuck" Carter-White told The Straits Times at a rest stop in Oregon.

Ryan Johnson, a 20-year veteran driver, wrote in a recent post on Medium: "Why is there only one crane for every 50 to 100 trucks at every port in America?"

"Think of going to the port as going to WalMart on Black Friday, but imagine only one cashier for thousands of customers" he wrote.

"Think about the lines. Except that at a port there are at least three lines to get a container in or out. The first line is the 'in' gate, where hundreds of trucks daily have to pass through five to 10 available gates. The second line is waiting to pick up your container. The third line is for waiting to get out. For each of these lines the wait time is a minimum of an hour, and I've waited up to eight hours in the first line just to get into the port."

Some ports are worse than others, and it is a very rare day when a driver gets in and out in under two hours. "Ports don't even begin to have enough workers to keep the ports fluid," Mr Johnson wrote. "And it doesn't matter where you are, coastal or inland port, union or non-union port, it's the same everywhere."

He added: "From personal experience, what used to take me 20 to 30 minutes to pick up at a warehouse can now take three to four hours.

"This slowdown is warehouse management-related: Very few warehouses are open 24 hours, and even if they are, many are so short-staffed it doesn't make much difference, they are so far behind schedule. It means that as a freight driver, I cannot pick up as much freight in a day as I used to, and since I can't get as much freight on my truck, the whole supply chain is backed up. Freight simply isn't moving."

Most port drivers are "independent contractors" paid by the load.

"Whether their load takes two hours, 14 hours, or three days to complete, they get paid the same, and they have to pay 90 per cent of their truck operating expenses (the carrier might pay the other 10 per cent, but usually less)," Mr Johnson wrote.

"In a majority of cases, these drivers don't come close to my union wages. They pay for all their own repairs and fuel, and all truck-related expenses. I honestly don't understand how many of them can even afford to show up for work. There's no guarantee of any wage (not even minimum wage), and in many cases, these drivers make far below minimum wage. In some cases they work 70-hour weeks and still end up owing money to their carrier."

The annual salary for a truck driver in the United States varies according to experience, and whether it is long-haul or short-haul trucking, but the average is roughly US$74,000 (S$101,000).

On top of this, there are the days away from home and family. Mr Carter-White has a three-year-old son, whom he does not see much. "The hardest, probably, is being away from your family most of the time," said the truck driver.

But trucking is in his family. His grandfather was also a truck driver. "It's in my blood," he said ruefully.

The shortage of drivers could hit 160,000 based on current trends, warned American Trucking Associations' chief economist Bob Costello in October. "This is a warning to the entire supply chain; to the motor carriers, to shippers, everybody. If nothing changes... this is where we're going to end up."

The pandemic has compounded the problem, with global supply chains disrupted and drivers coming down with Covid-19.

Also, with many states legalising marijuana, many drivers cannot pass drug tests that are mandated by the federal government - which still bans the drug. Tens of thousands of drivers have at some time or other tested positive, Mr Costello said. Most have not returned to work.

Then there is the issue of retirement as older drivers quit the industry.

"There's no one reason for the driver shortage," Mr Costello said. "That means there's no one solution for the driver shortage."