The Baltimore metropolitan area — though only No. 17 in population — ranks fifth in the nation in the average number of hours automobile commuters are delayed during peak periods, according to a national traffic study to be released today.

Commuters endure an average of 50 hours of delay each year, placing Baltimore behind only Chicago, Washington, Los Angeles and Houston, according to the Texas Transportation Institute's Urban Mobility Report. That ranking, higher than larger metro areas, reflects not just local commuters but also heavy through traffic on the Interstate 95 corridor.

That corridor is facing the prospect of even greater demands in the next several years as the Pentagon's Base Relocation and Closing process brings thousands of additional jobs to Aberdeen Proving Ground and Fort Meade — both a short distance off I-95 in metropolitan Baltimore.

"We know this is a very prosperous region and many of our congestion issues are related to the vitality of the economic environment of this region and certainly our proximity to the federal government in the Washington area," said Jack Cahalan, a spokesman for the Maryland Department of Transportation. He noted that the state is trying to ease congestion by adding express toll lanes in the White Marsh area — a project that costs nearly $1 billion.

But by other measures in the report, Baltimore commuters on average have an easier commute than their counterparts in similarly sized cities, said Shawn Turner, a senior research associate at the institute, pointing out that Baltimore's ranking may be distorted by the impact of I-95.

"For the city size, the commuting traffic is not as bad as other cities of comparable size," Turner said, pointing to the report's Commuter Stress Index, which indicates it takes 25 percent longer to commute at peak times than at non-peak hours, compared with 54 percent in the worst metro region, Los Angeles. That earned Baltimore a 25th-place ranking, but it's still a deterioration from 2008.

Turner said that for commuters whose route to work puts them on the I-95 corridor — such as those coming to the city from Harford County — the high ranking on hours of delay is "getting closer to what they're experiencing" than the commuter stress measure.

The report indicates that a long-term trend of worsening commutes is continuing in the Baltimore area. In 1982, according to the institute, the region's auto commuters endured 12.6 milllion hours of delays on the roads. In 2009, that total had risen to 82.8 million. The average per driver per year climbed by 39 hours — the fourth worst track record in the country.

While traffic congestion is universally loathed by those stuck in it, traffic jams are also a byproduct of prosperity. The institute's figures show that nationally, traffic delays and their resulting costs dropped sharply between the boom year of 2007 and the bust that was 2008.

Turner said the 2009 figures show a modest rebound in congestion over 2008. "Sneak peeks" at preliminary figures indicate the backups continued to build in 2010, he said, adding, "From what we're seeing it's starting to rain again."

Metropolitan Washington ranked close to the top in many measures of congestion, tying Chicago for first with an average 70 hours of annual traffic delay per auto commuter. Unlike Baltimore, it ranked near the top in commuter stress and other measures of peak commuting times.

The institute's report mirrors Census data showing that Maryland has the second longest average commute in the United States, and ranks dead last in its percentage of workers who enjoy easy commuting times. According to the 2005-2009 U.S. Census American Community Survey, fewer than 19 percent of Marylanders who work outside their homes can get from home to work in less than 15 minutes.

The institute urged policymakers to undertake a "diversified" effort to increase road and transit capacity in high-traffic corridors. "If the history associated with every other recovery is followed in this case, congestion problems will return when the economy begins to grow," the report said.

Pete Ruane, president of the American Road & Transportation Builders Association, expressed hope the report would motivate Congress to quickly pass a new six-year transportation spending bill.

"Congress and the president can do something about it by passing a robustly financed long-term highway and transit bill, which is more than 15 months overdue," he said. "Robust new investments aimed at creating additional transportation infrastructure capacity and providing more travel options will create jobs, facilitate economic growth and get America moving again."

Meanwhile, the American Public Transportation Association pounced on the institute's numbers showing that about $19 billion in congestion costs were saved in 2009 through mass transit services.

"There is no doubt that expanding public transportation use is key to reducing traffic congestion," said the association's president, William Millar. "Clearly, even if you don't ride public transportation, it is still in your best interest to support investment in public transit. Better public transportation in your community means less congestion on the roads."

The report indicates that Baltimore benefits more heavily from public transit than several regions with greater populations. It put the Baltimore's savings at 13.2 million hours in 2009 — ninth in the country and about twice the savings in the much larger Houston area. The cost savings for Baltimore commuters came to $323 million, according to transportation institute.

Cahalan said the results validate Maryland's emphasis on transit projects, including the proposed Red Line light rail system in Baltimore.