Once again, there is nothing casual about the fast-casual sector's ascent as the growth engine of the U.S. restaurant industry. Fast-casual brands in Technomic Inc.'s Top 500 Chain Restaurant Report increased their collective annual sales by 12.8 percent to $30 billion in 2014, and that growth rate was nearly double the next-largest increase from any other restaurant segment.  Click here to view the full-size graphic.

The Chicago-based market research firm disclosed the finalized numbers for its annual ranking of the 500 largest chain restaurants, which revealed that fast casual's one-year growth rate exceeded its five-year compound annual growth rate of 11.7 percent, suggesting that fast casual still has ample momentum for sales and unit expansion in the United States.

"Whether they offer the customization of a build-your-own format or just their made-to-order signature dishes, fast-casual chains clearly hit the sweet spot with consumers," says Darren Tristano, executive vice president of Technomic. "The winning formula of high-quality menu items in upscale settings, with high-touch service at prices between fast food and casual dining, can be applied to any kind of food and is powering growth in segments from burgers and barbecue to sushi and pizza. We'll continue to see fast casual drive much of the sales growth in the restaurant industry for years to come."

Four of the five fastest-growing brands of the past year came from fast casual, including the first build-your-own pizza chain to crack Technomic's annual ranking of the 500 largest restaurant chains, Pieology. The customizable-pizza concept increased its annual sales 230 percent from a year earlier, to $44.6 million in 2014, when its unit count nearly tripled to 42 locations.

Fellow fast casuals PDQ and BurgerFi more than doubled their annual sales with increases of 119 percent and 111 percent, respectively, and finished No. 2 and No. 3 on the fastest-growing brand ranking. Del Frisco's Grille followed with a 58 percent sales increase for 2014, and newly public "better burger" brand The Habit Burger Grill placed No. 5 with a 46 percent gain.

Each rapidly growing brand faces stiff competition within its peer set for the same real estate and management talent—let alone for the market share they all hope to take from limited- and full-service rivals—so they all look to differentiate in meaningful ways.

Pieology, for instance, offers unlimited toppings on its pizzas for one set price, while PDQ touts the complete absence of freezers and microwaves in its family-friendly restaurants. BurgerFi cultivates an eco-friendly reputation with chairs made from recycled soda bottles and buildings made from other recycled materials.

Fast casual also dominated sales growth among larger restaurant chains with at least $200 million in annual systemwide sales, Technomic found. In that group, Jersey Mike's Subs increased its sales 30 percent to $523 million in 2014, ranking just ahead of Dickey's Barbecue Pit, which recorded a 29 percent gain and $426 million annual sales. Even off a 10-figure base, Chipotle Mexican Grill increased annual sales 28 percent to $4.05 billion.