DALLAS -- The last thing a supermarket shopper wants to see is long lines and empty registers. It can lead to bad behavior on both sides of the checkout lane.

Ten years ago, shoppers envisioned a day when radio-frequency identification tags would allow them to whisk shopping carts through a checkout without unloading them -- or bypass the checkout lane and ring up groceries as they walked through the store.

But RFID never got cheap enough for razor-thin grocery margins. And we're still stacking groceries on conveyor belts, a 19th-century invention.

Year after year, retail trade shows buzz with the prospects of new checkout technology. But the pedestrian task of paying for groceries mostly still depends on clerks and shoppers being efficient.

There have been some innovations in checkout lanes, and shoppers will see a few more over the next couple of years. Smart-phone scanners and technology that keeps up with the flow of shoppers may speed up shopping trips, but many chains say they're finding that their employees are the best weapon against long lines.

More stores are reconfiguring their express checkouts with one line leading to multiple cashiers, which has been proven to be speedier. That system keeps shoppers from developing line envy.

Trader Joe's, for example, uses a single line for express checkout. Some Whole Foods stores have self-checkout registers, but for quick trips, the single line leading to several cashiers is considered faster, Whole Foods Market Southwest region President Mark Dixon said. Kroger added an express checkout configuration in some of its larger stores.

Choosing the right line can be frustrating even for a scientist.

Dick Larson, a Massachusetts Institute of Technology engineering professor who's known as "Dr. Queue" because he studies the psychology of waiting in line, says a trip to the grocery store initiates "all sorts of queue calculus. Do I buy that 13th item and then have to stand in a long queue? Do I try self-checkout, risking that I'll not know how to do the fresh produce? Do I join the slightly longer human-gated queue because the checkout clerk there looks a lot speedier than the one serving the shorter line?"

Kroger has been running commercials touting its new checkout system, which monitors customers coming in the door and estimates how many of them will need a lane open in 30 minutes.

But the system relies on managers paying attention to it and opening registers before shoppers get there.

"We know people like our stores, but when they're ready to go, they want to be out the door fast," said Kroger Southwest President Bill Breetz.

The new system was installed in all Kroger stores at the end of last year.

Kroger has one store in Cincinnati with a scanning tunnel that races groceries through what looks like an MRI machine. But items have to go through one at a time, and Kroger has no intention of rolling the system out nationwide.

The tunnel "is just a little faster," said food analyst Phil Lempert, editor of The Lempert Report. "Most consumers would rather have a competent cashier and bagger than any new technology. But what people do trust and value is their smart phone, and that's an easy next step for the industry."

Supermarkets are holding off on new hardware purchases and instead spending on software, said Jerry Sheldon, vice president of technology for IHL Group, a research firm that specializes in self-service technology. "Today people believe that consumers will already own the hardware and bring it with them."

Last June, Massachusetts-based Stop & Shop began letting shoppers use their iPhone and Android smart phones to scan and tally groceries and bag items while they shopped. The grocer has expanded its application, called Scan It, to more than 40 stores.

Shoppers are embracing it, Mr. Lempert said. "They say, 'It's my phone, and I trust it more than some company's technology, and I'm in control of it.' "

Mr. Dixon said Whole Foods is experimenting with technology, including Square readers that plug into iPhones and swipe credit cards and other handheld devices.

"Some of it works, and some of it doesn't," he said. "At the end of the day, nothing beats having plenty of registers and staffing them right."

One of Whole Foods' busiest Texas stores, in its hometown of Austin, has 120 cashiers, Mr. Dixon said.

"We don't stand there with a clock watch, but when we see it's getting busy, we can page 5 to 20 people to stop what they're doing and assist with bagging."

For many, self-checkout is a salvation. Others still can't master it.

First installed in 1998, self-checkout lanes have improved significantly but are old hat now. Stores are mostly spending money to replace worn-out self-checkout registers, but it's not going away, data from IHL Group show.

Self-checkout registers are expensive, at $75,000 to $80,000 for a four-register system, Mr. Sheldon said. Shipments of self-checkout hardware are forecast to grow a more modest 3 to 4 percent a year.

Grocers aren't giving up on making customer exits more efficient in some basic, low-tech ways.

At Trader Joe's in Manhattan, employees guide shoppers with signs on tall poles that read "Middle of the Line" and "End of the Line." During peak times, the line routinely exceeds 200 people and snakes around the entire store heading to 25 cashiers.

First Published March 25, 2012, 4:15 a.m.