WASHINGTON — With a growing number of Americans downloading movies and television shows, the nation’s broadband Internet has been picking up the pace to keep up with the demand.

According to the Federal Communications Commission’s fifth Measuring Broadband America report, the average download speed for American subscribers tripled between 2011 and 2014.

The average U.S. download speed was 31 megabits per second — Mbps — in September 2014, compared to 10 Mbps in 2011 and 15 Mbps in 2012.

Not all broadband Internet is created equally, with cable Internet speed hurtling forward, while DSL speeds have remained flat.

Cable’s most popular service tiers found dramatic increases in the past three years, from approximately 50 Mbps in 2011 to 105 Mbps in 2014.

Conversely, the maximum speeds for DSL were largely unchanged.

“There is a growing disparity in most download speeds tested between many DLS-based broadband services and most cable-based broadband services,” according to the FCC report’s executive summary.

The United States has long lagged behind other countries in Internet speed, largely due to an older infrastructure.

A recent study by Akami Technologies, a cloud services provider, ranked the U.S. 17th in the world in Internet connection speed, with South Korea, Hong Kong, and Japan topping the list.