THEN AND NOW: 14 photos of drive-thrus that show how much they've changed

• Founded in 1921, the Pig Stand in Dallas, Texas, was the first restaurant that was specifically designed to serve people in their cars.
• The subsequent rise of drive-in dining in the late 1920s and early 1930s paved the way for drive-thru restaurants to take off in 1950s.
• Red's Giant Hamburg, which opened in 1947, was among the first restaurants in the US to have a drive-thru window.
• By the 1970s, many of today's major fast-food chains began installing drive-thru windows.
• Today, drive-thru service is more efficient than ever before.

Today, it's hard to imagine a world without drive-thru restaurants. But people weren't always able to grab a quick meal without leaving their cars.

Since drive-thru service first emerged in the 1930s, the convenient innovation has become more ubiquitous and efficient than ever.

Below, see the evolution of drive-thru windows throughout American history in 14 fascinating photos.

In 1921, entrepreneurs Jessie G. Kirby and Reuben Jackson opened the first restaurant that was specifically designed to serve people in their cars.

At the original Pig Stand in Dallas, Texas, carhops would take motorists' orders as they pulled up in their automobiles, allowing drivers to grab a quick meal without leaving their cars, according to the Texas Observer.

Kirby and Jackson's restaurant was an instant hit, according to Oak Cliff Advocate magazine, and quickly expanded into dozens of locations in several states.

Soon after, drive-in chains like Maid-Rite and Carpenter's Sandwiches began popping up all across the US, forever changing the way Americans eat.

The popularity of drive-in dining in the late 1920s and early 1930s paved the way for drive-thru restaurants to catch on in the mid-20th century.

While drive-in eateries are less common now, some have stuck around.

Founded in 1953 as the Top Hat Drive-In restaurant, Sonic has since expanded into America's largest chain of drive-in fast-food restaurants, according to the Oklahoma Historical Society.

At the time of writing, the company has 3,613 locations across 45 states in the US.

The fast-food joint has retained its original concept, created by founder Troy Smith, in which carhops on roller skates deliver food to diners in their cars. Today, however, many Sonic locations also offer drive-through service.