Houston drivers can't rejoice in much as they plod along crowded streets and highways, but data released Monday suggests congestion improved between 2015 and 2016 just enough for them to cook pizza rolls, maybe even microwave popcorn if they have a long commute.

In its latest annual ranking of congestion around the world, TomTom - which operates mapping and traffic software common in car navigation systems - found Houston traffic improved slightly last year from 2015.

Of the 25 worst U.S. cities for congestion, Houston was the only one where congestion decreased from 2015 to 2016.

Officials with the Houston-Galveston Area Council have cited job losses as one reason traffic along some routes is easing. Losses in the energy sector have also been blamed for deep reductions in commuter bus use, according to Metropolitan Transit Authority officials.

Other factors might have also decreased average commute times in the area by affecting the math, said Nick Cohn, senior traffic expert at TomTom.

"In 2015, Houston had so many days that were affected by flooding," Cohn said. "I know you had days in 2016 affected as well, but it appears more days were affected by flooding in 2015."

Completion of major freeway projects - such as the Grand Parkway - and movement of jobs around the region can also affect the results, Cohn said.

After two years of drivers spending 25 percent more time behind the wheel as a result of congestion, last year Houstonians only wasted 24 percent of their travel time, compared to free-flow traffic conditions. That and other changes to travel patterns led to the extra time drivers spend on the road during peak congestion dropping from 34 minutes in 2015 to 32 minutes last year, for an hour of non-peak driving.

For example, someone driving from Spring to Houston's central business district could have a 60-minute round trip in no traffic. But that same round-trip drive would typically take 92 minutes each day, the extra 32 minutes caused by congestion.

Drivers didn't exactly rejoice at the extra time, noting a few seconds less after years of freeway work wasn't a fair trade.

"So what you're telling me is nothing has changed," said Todd Norton, 44, who drives Interstate 10 from Spring Branch to Loop 610 for work five days a week.

Reluctantly, Norton acknowledged with so much population growth in the area - the Houston region added nearly 160,000 people from July 2014 to July 2015 - it "beats everything getting worse."

The decrease might not be felt by many drivers, but did lead to Houston falling from 11th to 16th among U.S. cities in terms of congestion. Austin, at 15, now has the dubious distinction as having the worst congestion in the state. Worldwide, Houston was 117th, with Los Angeles and San Francisco the two U.S. cities to crack the top 30.

Dallas-Fort Worth, meanwhile, does surprisingly well for a large U.S. city, Cohn said. Dallas benefits from a combination of recent road improvements and jobs spread across the region and not just along key corridors as is the case in Austin - where a few bad routes weigh heavily on overall congestion.

Some caveats come with the rankings and data. The amount of time TomTom cites and uses to compare congestion and free-flow isn't based on how long it takes to travel in the region, where some commutes are far longer than in other metro areas. The 32 minutes in Houston represent the extra time local drivers waste because of traffic during an hour of driving.

In Chicago, tied for 13th among U.S. cities, drivers spend a higher percentage of time in congestion, but waste 29 minutes - three minutes less than in Houston - because of differences in how far people travel.

A number of traffic rankings, including the Texas A&M University Transportation Institute's Urban Mobility Report, focus on comparing conditions with and without traffic.

Critics say it is a misleading way to compare cities because sprawling ones like Houston mean it is possible to have no congestion and a lengthy commute, and more urban areas can have a lot of congestion, but commutes of a few blocks instead of a few miles.

Within the region, routes have experienced changes, even if the average commuting times only moved slightly.

"Westheimer has gotten better east of (Loop 610) and worse west of it," Cohn said.