Airport. Doctor's appointment. School play. Job interview. A delivery.

If you absolutely, positively, most-definitely have to get there on time, Portland is the nation's sixth worst place to be during rush hour, according to an annual study of national driving habits.

In fact, it appears that the same sprawl-fighting policies that have created shorter commutes in the Portland metro area have also resulted in some of the nation's most stressful and unpredictable peak commuting hours.

Heavy traffic

Most unreliable commuting times in U.S.

(Time that should be planned during rush hour for normally 20-minute trip)

1. Washington D.C. (114 minutes)

2. Los Angeles (99 minutes)

3. New York-Newark (89 minutes)

4. Bridgeport-Stamford CT-NY (88 minutes)

5. Provo (87 minutes)

6. Portland (85 minutes)

6. Austin (85 minutes)

Source: Texas A&M Transportation Institute 2012 Urban Mobility Report

A tight, circular freeway system within the growth boundaries tends to create bunched-up morning and evening commutes that can seize up after just a couple of simultaneous fender benders, said David Shrank, one of the authors of the Texas A&M Transportation Institute's new Urban Mobility Report.

The report analyzing congestion patterns in 498 of the nation's urban areas in 2011 ranked the Portland region sixth worst for delays during peak commuting hours and, in a tie with Austin, Texas, sixth on the list of the most unreliable freeway commutes.

In fact, rush-hour travel times are so unreliable in the Portland area that drivers headed to an important appointment 20 minutes away should probably give themselves 85 minutes if it involves freeway miles, Shrank said.

Because of high-density planning and strict growth policies, Shrank said Portland-area residents tend to have shorter commutes to work and home than people in comparably sized cities.

"But these can be intense, short trips with frequent delays," Shrank said. "With a single crash or a breakdown or bad weather and things can go downhill real fast. It really plays with the reliability and predictability of getting to your destination."

However, Joe Cortright, a Portland economist and an outspoken opponent of plans to build the $3.5 billion Columbia River Crossing, said the Texas A&M Transportation Institute's findings are deeply flawed.

Cortright said in an email that the report makes the region's congestion look worse it really is.

"It ignores differences in trip distances among metro areas," he said, "and how trip distances have changed over time. In Portland, we drive about 20 percent fewer miles per day than the average resident of a large urban area."

The time Portland-area drivers save from commuting shorter distances, Cortright said, isn't reflected in the calculations.

Shrank disagreed, noting that, despite frequent delays during morning and evening peak hours, the Portland area's shorter commuting distances are one reason it didn't place higher in the overall rankings of America's most-congested urban areas.

After traffic flow outside peak hours (6 a.m. to 9 a.m. and 4 p.m. to 7 p.m.) is factored into the calculations, Portland ranks 17th on the list of America's most-congested cities. That's the same position it held last year. In 2010, the region was ranked 24th.

"We do have distance included in our measures," Shrank said. "Portland's population is 23rd in the nation, so its overall congestion ranking is not that striking. There are quite a bit of short trips happening. But the trips are pretty congested during peak hours."

The region's investment in public transit and bike lanes has also provided noticeable benefits over urban areas with similar populations, he said. "It will be interesting to see what things look like 20 years from now."

Seattle tied with Philadelphia for the nation's ninth worst gridlock, while Salem and Eugene ranked 68th and 99th, respectively, according to the study.

For the fourth year in a row, Washington, D.C., had the dubious honor of being named the nation's most-congested city by the report, followed by Los Angeles, San Francisco-Oakland, New York-Newark and Boston.

The study estimates that average Portland-area driver wasted $937 and 44 hours stuck in traffic jams in 2011, burning through 21 gallons of extra fuel. Collectively, the Portland metro area lost about $1.1 billion of gas and time in traffic.

Traffic engineers and planners frequently use the annual report to help solve congestion problems.

But this is the first year that Texas A&M researchers, using data from Seattle-based traffic reporting service Inrix, the U.S. Transportation Department and state transportation departments, have measured and ranked the degree of commuting unreliability on urban highways and interstate freeways.

Shrank and the study's other researchers assigned cities a Planning Time Index, a tool looking at the total travel time that should be allowed during rush hour for an important trip that would take 20 minutes in free-flowing traffic on the freeway. If the PTI for a city is 3.00, a traveler should allow 60 minutes to guarantee that he arrives on time for an important event.

If you want to be on time 19 out of 20 trips, Portland's PTI is 4.26 – multiply that number with the usual travel time. That's the sixth worst PTI in the nation, according to the study.

So, give yourself 85 minutes for destination that is normally 20 minutes away (or more than two hours for a 30 minute trip). Of course, the mathematical index applies only to trips on limited access roadways such as state highway and interstate freeways.

Several other transportation studies, including a 2011 Inrix scorecard, have found that Americans are driving less, even as the Great Recession fades away. According to the Texas A&M study, however, traffic congestion in U.S. cities has remained "relatively stable" over the past two years.

While congestion nationwide is still below the 2005 peak, the institute's researchers said they expect traffic jams to worsen as the economy continues to recover.

Realizing how much stock transportation officials put in the annual Urban Mobility Report, Cortright worries that such predictions will embolden supporters of costly highway projects such as the Columbia River Crossing.

Cortright remains convinced that both driving and gridlock on the decline.

"This decline in driving – which is part of a long-run adjustment process to the increase in gas prices over the past several years – is manifesting itself virtually everywhere," Cortright said, "except in the Urban Mobility Report."