Internet shopping by consumers and the chronic driver shortage are responsible for part of recent growth in intermodal operations, according to a commentary published last fall by FTR Associates. Part of the surge involves 28-foot pup trailers riding on flatcars, a trend that defies conventional wisdom regarding piggyback efficiency, says researcher Larry Gross.

Fifty-three-foot “pig” trailers carry more cargo per “lift,” the process of picking up a trailer and placing it aboard a special flatcar, then removing it at the other end of the line. Then why use 28s? E-commerce has resulted in the shipment of millions of individual parcels vs. truckload lots, and a merchant’s shipments over a given lane, say, Chicago to Los Angeles, aren’t enough every day to fill a 53, but can fill a 28.

Yes, two or three shipments can be consolidated into a single long trailer, Gross writes. But that would require breakdown of the combined load at the L.A. end. Eliminating the extra parcel handling saves more money than is spent for the extra lifts. (That’s been true of parcel shipping for many years, but e-commerce has added to it, Gross writes.)

The growth of piggyback, meanwhile, also defies the efficiencies of domestic containers. A big steel box carries about as much as a 53-foot trailer, but doesn’t have the weight of axles, brakes, wheels and tires, suspensions, and landing gear. Moreover, containers can be double stacked, theoretically doubling the amount of cargo carried by a train of a given length, and all the efficiencies that implies.

But piggyback has nonetheless grown because a shortage of drivers forces motor carriers to send trailers – usually 53s – by rail instead of over the road, Gross says. Assuming railroad service is good, transit times can beat even team-driver operations on long hauls. Some of that time is eaten up in the lifts at either end of a haul, and the lifts require expensive machines that eat fuel and need people to operate them.

Of course, that trailer must be pulled to the departure terminal and away from the destination yard, requiring two tractors and drivers instead of one. So there’s still business for truck builders and jobs for truckers.

Then again, daycab tractors used for local and regional service cost far less than the nicely equipped sleeper-cab tractors needed to attract and hold long-haul drivers, the then-president of a major truck manufacturer once complained to me. And because mileage of the daycab unit is often lower than the OTR type, it can be kept longer and, even at an advanced age, can be maintained easier than one that’s thousands of miles from home.

Plus a local or regional driving job gets a guy or gal home frequently, so is more attractive to people who want to have an enjoyable life and not just an all-consuming job and could help out with the driver shortage. Researchers say that’s especially true of millennials, who don’t have the “work ethic” of their elders. (Sorry, but there’s a lot to be said for the young folks’ attitude.)