Classic Automotive History: The Rise and Fall Of The American COE Semi-Tractor

(updated and expanded)  From the late forties through the seventies, the Cab Over Engine (“COE”) semi-tractor was the Brontosaurus of the Road.  You’d see them happily plodding along in the slow lane pulling all sorts of cargo coast to coast.  Today, you could spend an entire day on an American highway and not see a single one. Why did they disappear?

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While the COE format has existed almost as long as internal combustion trucks, they started to become more common in the mid-late thirties as a way to increase payload space within given length restriction.

GMC aero truck

The aerodynamic era produced some spectacular limited-production COE truck-trailer combos, like this beer delivery combo with a GMC tractor.


Fageol COE 1940simage: Dick Copello’s Flickr page

 COEs became even more common after WW2, as highway haulage increased. This 1940s Fageol, a rather rare truck, is still from the era when style was important to trucks. That would soon change.

mack COE himage courtesy

The COE really came into their element in the 60s and 70s as the Interstate Highway System built out and truck traffic and trailer lengths grew. Because most states in the eastern half of the country had very restrictive laws about total over-all vehicle length, equipment design had to think within the proverbial box.This Mack COE with a 40′ semi-trailer represents the typical over-the road semi-trailer rig in the US during the pre-deregulation era.

The only way to squeeze a larger trailer into the same length and width “box” was to shrink the cab.  The ad copy of the tractor OEMs shows that they competed to offer the shortest Bumper to Back of Cab (BBC). Operator comfort played second fiddle to the squeezing out every cubic foot of cargo space.

Peterbilt lwbimage courtesy

During this era many of the western states had a different regulatory regime that emphasized spreading a larger amount of allowable weight over a longer span to reduce to damage to the road. This Peterbilt is a classic “West Coast Truck”, with an enormous wheelbase on the tractor, due to very generous overall vehicle lengths allowed. The higher weight limits in the West also meant that three axle truck pulling a two axle trailer was a more common format there.

This Hostess-Wonderbread Freightliner is a regulatory Frankenstein. The use of a dromedary box on the tractor transforms it from a tractor trailer combination to a truck and trailer with a larger permitted overall length. In this case you could call it the Twinkie Defense to restrictive regulations.

This Thrifty Drug GMC Astro 95 is pulling a set of “Wiggle Wagons” in mid 1980s Northern  California. Note the Multiple License Plates required for each state the tractor operated in and the “Dragfoiler” air deflector and traction chain hangers on the trailers.  Chain racks configured this way are still the preferred configuration. A good driver can hang a complete six chain set of iron in about 30min versus the 50-60min if they are all hung on the tractor. The square tanks allow additional fuel to be carried in the same space along the frame rail; the ability to operate for 2-3 days on a single tank became more important after the ’73 and ’79 shortages.

The Last of the Coehicans? This Swift Freightliner Argosy  is the spiritual heir to the Thrifty Astro as it’s highly probable when I took this shot it was assigned to the account delivering to Rite Aid stores, the successor to Thrifty-Payless. When Freightliner discontinued the Argosy in 2006 is was the end of the line for the COE Semi-Tractor in the US.

The Freightliner was the most iconic of the COE trucks, given that its cab was built with only minor changes for almost half a century since the first of this series arrived in 1950. Its lightweight  aluminum cab also meant more weight for payload.

Their virtual extinction was a direct result of the proverbial asteroid of the 1982 Highway bill; previously the total length of the tractor-trailer combination was limited;  the game changed to limiting only the length of the trailer(s) (to 53′).  It took awhile but the legislative asteroid changed the regulatory environment to favor the conventional hooded tractors.

Once the regulatory limits on tractor length were eliminated, COEs fell out of favor for as they were cramped and less safe relative to a tractor with a hood.   Wheelbase and suspension being equal, a COE with the driver sitting atop the front axle delivers inferior ride quality to a conventional.


Freightliner COE allied

Back and kidney problems were a common occupational hazard for the drivers of the era. Slips while accessing the cab were a frequent cause of injuries.  One anecdotal story had Workman’s Comp claims drop by 50% when a major trucking company eliminated COEs from their fleet.  As the freight business evolved into larger carriers keeping drivers on the road for  three to four weeks or more at a time, the smaller living spaces offered became a disadvantage.

COEs still thrive in a few niches where space and/or a short wheelbase is at a premium.  This pair of  Freightliners configured for delivery of construction material is representative of the niche where they are still preferred.  In a modified form you also still see them as Low Cab Forward Refuse Trucks like the Peterbilt 320 and Mack MR.

Mercedes COE truck

The situation in Europe is quite the opposite. Strict overall vehicle lengths in most countries there have made the COE the only way to go for long-haul trucking, and it has been developed to a high state of comfort and efficiency. With the cabs riding on their own air-spring suspension, the ride has become comfortable, and the sleeper cabs quite commodious. Will the COE ever return to favor in the US?

Marmon COEMarmon COE  image: Dick Copello’s Flickr page