Driver Ergonomics: Round Pegs and Oval Holes

Driver demographics are driving changes in cab designs.

May 2014, - Feature

by Jim Park, Equipment Editor - Also by this author

SHARING TOOLS        | Print Subscribe

As well as being in short supply, trucking’s new recruits are also, shorter generally, and thinner, as well as less likely to want a truck to look and feel like a truck. The challenge for truck makers comes in designing truck cabs to fit an expanding body-size profile, while making the driving environment appealing to people who have different expectations about trucks – all without alienating the existing driver population.

Jason Spence, Volvo Trucks product marketing manager and formerly market research and industry trends manager, says there have been subtle but obvious changes in drivers’ weight and form in recent years. Spence says drivers are getting smaller.

“There has been a downward shift in the prevalence of what we describe as morbid obesity to more of an overweight status, and even further into what you could call a normal body mass index,” he says. “There are a number of reasons for that, but it does not appear to be because of improving health. The driver population isn’t trimming down; the larger ones are being trimmed out.”

Volvo’s analysis shows in 2008, the average driver weight was 232 pounds, but 2013 it was down to 216 pounds.

Volvo uses the National Institute for Occupational Safety and Health’s large-scale body-type surveys, and Spence has seen a change in the group representing the 95th percentile male to the 5th percentile female.

“The range in body size has increased with the influx of smaller Latino, Eastern European, and South Asian males and generally smaller female drivers,” Spence notes.

This can affect design items such as door handle placement, the amount of force required to open the door and even the step placement, considering the height from the ground and the distance between the steps.

To put it succinctly, truck cabs and all their amenities and service points have to comfortably accommodate body types ranging from something like a 5-foot, 2-inch, 110-pound female to a 6-foot, 5-inch, 300-pound male.  

Truck makers have to account for various eye positions relative to the dash behind the steering wheel, visibility over and around the hood and the mirrors. Drivers have to be able to reach the inspection points on the engine, and, of course, have the strength to open the hood.

Andy Weiblen, Peterbilt’s assistant chief engineer, says the force required to open the hood on the Model 579 is about half that of previous truck generations.

“I think it’s about 25 pounds now,” he says. “And our clutch pedal now needs about 30 pounds of force to depress, where it used to be closer to 50 pounds.”  

Overall, Peterbilt has increased seat adjustment by 20% and increased steering column adjustment by 77% in the new product line, and it seems to have satisfied the objective.

“We had a woman who was 4 feet, 11 inches visiting the Paccar Technical Center in Renton, Wash., say the truck fit her,” Weiblen says. “She was very surprised because she had had trouble getting a car or van to fit her small frame.”

When Paccar was developing its new cab dimensions, shared between the Kenworth T689 and Peterbilt’s Model 579, it invited 850 drivers to try the cab on for size. In fact, the drivers decided the dimensions of the cab using an adjustable mock-up of the cab that could be lengthened or shortened in all directions. The mock-up also allowed them to adjust the space between the driver and passenger seats for access to the sleeper, optimize the steering column position and how foot pedals should be aligned and distanced, and more.

“That exercise provided us with the right size for the cab and entryway to the sleeper,” says Jim Bechtold, Kenworth’s director of product planning.

“From the pressure required to flip a switch to the effort required to open the hood, driver size and weight play a role,” says T.J. Reed, director of product marketing at Freightliner Trucks. “We have come up with six or seven body types, and we create digital mock-ups first. And then we build physical mock ups and get real people that fit the type and get them to try the design.”

Reed notes that in working with the Women In Trucking association, the company has refined things like the seat travel and the steering column in the Cascadia. “Now, pretty much anyone can reach the pedals and drive a Cascadia,” Reed says.

DTNA engineering uses a range of digital mannequins developed from a
statistical analysis of measurements taken from actual truck drivers.
DTNA engineering uses a range of digital mannequins developed from astatistical analysis of measurements taken from actual truck drivers.

Next gen drivers

A number of years ago, the International Brotherhood of Teamsters tried to write into its National Freight Agreement a “belly-room clause” that set minimum dimensions for the space between the steering wheel and the seatback. That effort didn’t move forward, but what came of the discussion between the Society of Automotive Engineers Cab and Occupant Environment steering group, the union, truck makers and other interested parties was a better understanding of the fact that the typical truck driver was not representative of the male population in general.

Jerry Hubble, chairman of the SAE Cab and Occupant Environment steering group, says it led to a more exhaustive study of truck driver body types and brought us closer to today’s design parameters.

“That exercise brought us the Sanders Study [also known as U.S. Truck Driver Anthropometric Study and Multivariate Anthropometric Models for Cab Designs], which gave us parameters for headroom, belly room, shin-to-dashboard clearance, etc., based on truck drivers’ dimensional parameters,” he says. “Compared to the general population, the truck driver is bigger in many ways than the 95-percentile male.”

“The other end of that spectrum,” notes Hubble, “are women, Asians, Latinos and others who are typically slighter in build than what we once defined as the typical truck driver. SAE’s goal now is to accommodate 95% of the truck driver population.”

More recently, the University of Wisconsin-Stout in Menomonie, Wis., partnered with Women In Trucking to identify opportunities for improvement in the designs for seats, dashes, steering and in-cab ergonomics for female drivers. Ryder System got involved with the research and identified custom vehicle designs that better meet the needs of female drivers.

“We found there was a lot of room for improvement in some of the cab designs, especially related to entry and exit as well as how the seat and dash are positioned relative to the pedals,” says Scott Perry, Ryder’s vice president of supply management. “Externally, we saw the need to lighten the pull pressure on some fifth-wheel locks. We saw hoods that were a little heavy, so there’s room for lift-assist devices or lighter hoods. There’s a lot when you get into it. Ryder is moving forward with some of these changes and we’re pushing the OEs to go further.”

Driver comfort

It’s one thing to shoehorn larger or smaller bodies into the cab. It’s another to keep them comfortable and satisfied with the environment. Seating plays an important role, since that’s figuratively where the rubber meets the road.

Volvo’s Spence advises that seats from different manufacturers come in different widths to accommodate different behinds. “Seats are customer choice items, so the seat you choose should be one that will keep you happy,” he says.

Women In Trucking says more than 200,000 women are employed as drivers, prompting truck makers and fleets to evaluate how well their trucks meet women’s needs.
Women In Trucking says more than 200,000 women are employed as drivers, prompting truck makers and fleets to evaluate how well their trucks meet women’s needs.

In bygone days, truck and cab design seems to have been driven by form rather than function. Compare, for example the Mack R-model or the Peterbilt 359 cabs to the present models. Although many drivers miss the classic look, they also were smaller, noisier, hotter, had less room and were measurably less human-friendly.   

Mack’s construction product marketing manager, Stu Russoli, says the Mack cab, with its history in the construction and severe service sectors, has undergone quite a transformation in accommodating non-traditional sized drivers while bringing a distinctive style to the product.  

“Styling is very important, and it’s a fine line between too trucky and too automotive,” he says. “Today we have a wide variety of expectations to meet, from the old-guard driver to the younger people who want their truck to look and feel like a car. We are constantly surveying to stay ahead of what the market seems to want.”

Research for the Saunders Study was done more than 40 years ago, and it served designers well for a long time. We can be sure, with the emergence of a different sort of truck driver, that the next round of significant changes won’t wait that long.            

Alarming alarms

Conversations about the in-cab environment also are increasingly addressing the question of how to best deal with the amount of information being served up to drivers in todays’ trucks.

The last thing a driver needs when something is going wrong is a confusing message about what’s going wrong. We’ve seen a proliferation of warning devices in truck cabs, and as yet, there are no standards for all those sounds and blinking lights.

T.J. Reed, director of product marketing at Freightliner Trucks, says a warning should alert the driver to the problem, while keeping the driver’s eyes focused on the road and their hands on the wheel, not get them searching around wondering what the beep or buzzer means.

Various eye-points are examined to ensure optimum visibility from the driver’s seat. There can be no compromises in here. 
Various eye-points are examined to ensure optimum visibility from the driver’s seat. There can be no compromises in here.

“Secondary devices that require an individual gauge or a module that goes to the B-panel is something else to search for on the dash,” he says. “We’re integrating these warnings into the cluster, right in front of drivers where they can see it.”

But since the A panel on most trucks is getting pretty full, where do we put the additional warning lamps?

Heads-up displays, or HUDs, are one option.

HUDs are still in the advanced concepts realm at the moment, says Andy Weiblen, Peterbilt’s assistant chief engineer.

“Some are projected onto windshields, but windshields in trucks are tricky,” he says. “They frequently need to be replaced, so having an embedded display wouldn’t work because the HUD would increase the replacement cost.”

Instead, Weiblen is looking at projection technology that would be dash-mounted and displayed through a signal combiner mounted on top of the dash.

“You can still see through it, but it would not be subject to the replacement costs,” he says. “Regardless of how we do it, we want to make sure the driver’s eyes remain focused on the road. We want the display as close to the line of sight as possible, as opposed to a gauge on the far right side that is blinking red.”


  1. 1. Jlc [ June 19, 2014 @ 12:08AM ]

    I drive a 2009 peterbilt day cab. I am 6ft tall add A quarter inch or so with work boots and weigh 195. I drive 3 to 550 plus miles a day. Put a wider seat with armrests helped a little on comfort. We go down ruff dirt roads so when you are cramped for space and are getting bounced around. It can become a very uncomfortable environment. You can't sit like lady in picture above for 14 hour days it'll hurt you. Besides just being shoehorned in. seat is all the way back pedals end where they should start pedals are way to close not just a comfort issue it can easily be a safety issue cause legs cant be extended you are kind of pressed between pedals and seatback with seat all the way back seat. won't lean back to get a comfortable position we are in This cab approximately 11 hours driving 14 work day. And steering wheel sure does come down enough but should go more forward. It's a constant adjusting seat and wheel to change the point of comfort which cannot be accomplished for entire body at once. I love my job but to be honest if I realized. trucks were so cramped I would have not became a driver it's when you get out there you figure out what is comfortable not in a mock up nothing is happening. And there is no stress and other traffic and obstacles that make a big difference on what is comfortable when the truck is doing its real job. I'm sure somewhere in the country we got Lil guys and they might think that bringing this and that a little closer makes it easier but trust me only for them. I realize it's a tough to make something for everyone. Toyota Tundra does it my wife 4 ft 11 fits and can even get to close. I fit 6 ft and can get way to far. Seems most trucks are solely for the little guys. Solution would be to add 6 to 10 inches to the cab so the seat could actually be adjusted to fit any one. Problem solved. I know weight is an issue with added material but this is possible seems. Crazy to think that drivers are mostly shorter and thinner.give them time they'll get fatter sitting there. And for shorter I work with 65 driver's even the shortest probably 5ft 2 has his seat as far back as possible and so many of us struggle with the space. Just wanted to share my view that. The majority is not happy in these trucks molded to fit a group . when. All could be changed. Very easily for all to be comfortable and safe. I honestly don't realize how it's legal to. MAKE a vehicle that is so limited. On a driver just cause he is a little taller or fatter or maybe both. It's not safe not to reach the pedals but just as dangerous being to close. Hope this reaches someone who can do something for the white black American worker since race was mentioned in this article glad to see we make sure others get the long straw because of race. I think it's a bad thing that in so many ways we are made to feel guilty for being white and full grown even when it comes to designing a truck which trucking is one of the most redneck job I can think of. Anyway let's just make Em right for everyone trucking is dangerous enough the driver must have room. And not be bunched up. Thank you not trying 6 upset or hurt anyone's feelings. Just want to see manufacturer build the absolute best and safest product for everyone. Thank you

  2. 2. Ricky Bobby [ July 11, 2014 @ 03:20PM ]

    Jlc go try one of the new Peterbilt 579s. That 2009 model you drive (unless its a 387/587) has a cab that's been around since the 80's. I'm 325 lbs and 6'3" without my Redwings on and I am very comfortable in the new Peterbilt cab.


Comment On This Story

Comment: (Maximum 2000 characters)  
Leave this field empty:
* Please note that every comment is moderated.


We offer e-newsletters that deliver targeted news and information for the entire fleet industry.


ELDs and Telematics

sponsored by
sponsor logo

Scott Sutarik from Geotab will answer your questions and challenges

View All

Sleeper Cab Power

Steve Carlson from Xantrex will answer your questions and challenges

View All