Category Archives: affordances

Electric Scooters and their Warnings: A Guest Post by Kim Wolfinbarger

Electric shopping carts are common in large grocery stores. Essential for users with mobility impairments, they are also helpful for pregnant women, elderly shoppers, and other who have trouble walking long distances.

A few months ago, my grandfather overturned such a cart in a parking lot and broke his hip. Interested in what might have caused the accident, I examined a similar cart at my local store.

in-storeWhile the cart appeared stable, red-and-white signs affixed to the inside and outside of the basket read, in large letters, “IN-STORE USE ONLY.” Two others warned, “INTENDED FOR USE INDOORS ON LEVEL SURFACES ONLY!” and “DO NOT TAKE THIS CART OUTSIDE THE STORE.” An instruction manual I found online had similar statements in several places.

instructionsHere is the problem: A customer who uses the cart while shopping will surely want to use it when taking groceries to the car. My grandfather lived independently and drove himself to the store, but rheumatoid arthritis made walking difficult. Using an electric cart made it possible for him to do his own shopping. While he most likely saw the warning, he may have dismissed it as a statement written to merely to discourage lawsuits. (This is speculation–he could not converse following the accident and died a few weeks later–but it is consistent with his personality.)

Clearly the manufacturer had anticipated that people would use the carts outside and thought this behavior might be hazardous.  But did the store share this concern? Since the cashier loaded the bags into his cart following the purchase, it appears that, despite the warning, the store expected him to drive the cart to the parking lot.


The signs and repeated warning statements in the manual suggest a mismatch between the design of the product and the expected behavior of users. So how should the problem be addressed?

  • If the carts are truly not stable outdoors, stores should not allow them to be driven into the parking lot. Instead, employees should carry out groceries for all customers who use a motorized cart.
  • Offering the service is not enough; some customers, not wanting to be a bother, will refuse assistance if asked. Instead, when the cashier begins checking out a customer with an electric cart, she should immediately summon a worker to load the groceries into a push cart and take the groceries to the customer’s vehicle.
  • Manufacturers should assume that customers will take electric carts outdoors and design them accordingly. Motorized scooters intended for outdoor use are widely available.
  • If they have not already done so, shopping cart manufacturers should implement similar stability features.  As human factors engineers have said for years, a warning is no substitute for good design.
  • Good warnings tend to have a “why” that informs the user about the hazard when that hazard is not immediately obvious. If you though the reason to keep the cart indoors was because you might be hit by a car, your decision to take the cart outdoors could be different than if you knew the cart were unstable.

Kim Wolfinbarger is the recruitment coordinator and an adjunct instructor for the School of Industrial Engineering, University of Oklahoma. Her research interests include usability, product design, industrial ergonomics and design for special populations.

Invisible Lines and Laundry Detergent

Consumer Reports tackled a pet peeve of mine: the invisible fill lines for laundry detergent. Most of you are probably using too much.. I finally took a sharpie to mine. Some excerpts from the Consumer Reports article:

“If the lines aren’t clear or are hard to see, it’s easy to overdose and use too much detergent,” says Pat Slaven, a program leader in our Technical department who conducted the detergent testing. “Plus, for all the products we tested, the line for a medium load—the most commonly done load—is less than a full cap, which makes it easier to use too much detergent.” The line for a maximum load is also typically less than a full cap.

Even a textiles expert can face issues with detergent caps. “The salesman who sold us our energy-efficient washer emphasized that we should follow directions to the letter—or fill line, in this case. Of course, I have to stand under a floodlight in the garage to see the fill line,” says Margaret Rucker, Ph.D., a professor of textiles and clothing at the University of California at Davis. “If a study on cap design hasn’t been done, then it should be,” she adds.

Another manufacturer has taken a different approach to solving the problem. “We feel the best practice is to include a picture of the cap on the directions, where we call out exactly where the dosage lines are on the cap,” says Bill Littlefield, executive vice president and general manager of branded products of the Sun Products Corporation, which makes All and Wisk detergents. Littlefield admits, “It’s a struggle to find proper dosage.”

Procter & Gamble, whose detergents include Cheer, Era, Gain, and Tide, also shows images of the actual caps and fill lines on its labels. “We have specific fill caps that are clearly marked, and we feel people understand the product,” says Lauren Thaman, a chemist and head of U.S. external relations at P&G.

Although the companies “feel” that consumers know how to use their product, field testing might show otherwise. Using a picture of the cap on the box separates the information from the action, adding an extra step.

Consumer Reports was tactful enough not to mention that overuse of detergent benefits the companies making the detergent bottles and their indicator caps.

Acoustic Information from Basketball Courts


I came across an article on ANSI standards that had an interesting human factors anecdote. Thought I would share:

It seems that a critical part any basketball game is the wood flooring, something which the fans generally take for granted, but not so the players. Basketball floors are highly engineered surfaces, made of three-quarter inch thick tongue-and-groove northern hard maple, laid on plywood and supported by sleepers. One manufacturer of the flooring, Robbins Sport Surfaces of Cincinnati, Ohio, even sells a floor that controls its acoustics so the sound of a bouncing ball is more uniform across the surface. A variation in the sound of the bounce could lead players to incorrectly assume there is a dead spot while running down the court for that winning lay up.

Are there other examples of surprising information sources in sports?

Map Information Visualizations = HOT!

I‘ve noticed a trend in the newsworld/blogworld recently. Everyone wants to represent everything on a map. Some of these are genius, others make me wonder “why bother?” I collected some of each for this post… but I warn you, once you notice this pattern you’ll start seeing it multiple times per day.

Job loss from (Usability note: good luck mousing-over your county)


Race in an area compared to toxic waste release from the


Electricity Visualized from (This link has many map options. Wind power pictured below.)


Immigrant Populations from the New York Times (Also an “explorer” graphic with interactivity)


Religion in the United States via the Wall Street Journal


That’s just a taste. Also see:

(post image:

Human Factors Potpourri (again)

Here are some more human factors-related items that have crossed my blog reader:

  • Twitter is hot!  Oprah recently twittered on her show and apparently fell victim to a usability problem:  the update button was non-obvious so she never posted her tweet (Touch usability)
  • Fellow HFE blog Real World Usability will be posting updates of the Ergonomics Society Conference via Twitter
  • A night at the hospital from the patient’s point of view.  Grad student Kathleen Von Eron-Sherman documents her experiences in the hospital through human factors-colored glasses (unfortunately this article is behind a pay wall or you can visit your local library).
  • The newly introduced Pedestrian Safety Enhancement Act of 2009 mandates that hybrid vehicles (which are whisper quiet) include noise to make them more apparent to pedestrians (AutoBlog)

Milk Jug Usability

Picture: David Maxwell, NYT

A square milk jug has lots of benefits; because of its square shape, they stack more efficiently compared to existing milk jugs.  The shape makes it so that cartons of milk won’t require milk crates.  The net result is reduced transportation costs.

However, it seems they are not so easy to pour. According to the NYT article, training was required to show shoppers how to pour without spilling.

Mary Tilton tried to educate the public a few days ago as she stood at a Sam’s Club in North Canton, about 50 miles south of Cleveland, luring shoppers with chocolate chip cookies and milk as she showed them how to pour from the new jugs.

“Just tilt it slowly and pour slowly,” Ms. Tilton said to passing customers as she talked about the jugs’ environmental benefits and cost savings. Instead of picking up the jug, as most peopletend to do, she kept it on a table and gently tipped it toward a cup.

The fact that training is required makes this jug seems like a lazy design.  There must be a simple design solution that keeps the benefits of square milk jugs but makes pouring “intuitive”?

Solution, or Mess? A Milk Jug for a Green Earth –