The contractions started just before 7:30 a.m., and Venita Cooper had to get to the Bethesda Navy hospital fast. The Fort Washington woman asked one little favor of her husband on the way out the door.

"The first thing I told him was, `Don't let me get caught on the Beltway,' " Cooper said. "He promised me he wouldn't."

Try as he might, Wesley Cooper couldn't quite keep that promise.

The couple found themselves trapped with thousands of others yesterday on the outer loop of the Capital Beltway, which seized up on all sides after a truck carrying 17 tons of explosive powder overturned in Virginia.

Transportation officials said the wreck toppled a cascade of commuter dominoes that tied up traffic from Springfield to Rockville, unmaking so many well-made plans -- and making the Washington area's ordinarily heavy congestion seem like the sniffles in comparison.

Employees were late for work, or never made it at all. Cars and trucks overheated in the sweltering gridlock of a hot June day. Tourists scrambled for impromptu hotel accommodations because they couldn't get out of town; parents missed child-care appointments because they couldn't get into town.

And, in at least one documented case about 6:10 p.m. on the inner loop in Alexandria, two girls were in a panic over a prom dress.

"What's going on over here?" asked Sequira Glover, 17, of Washington, laying on the horn of her brown Honda. "I've got to get to the mall! What is going on?"

Glover and her 10-year-old companion, Tamira Allen, were hardly alone in their frustration.

Government programmer Tars Hernandez, for example, celebrated his 37th birthday yesterday by stopping for gas after two hours and 45 minutes on the Beltway, preparing for another couple of hours behind the wheel before reaching home in Annapolis. He already had missed Lamaze class with his pregnant wife.

"It's way out of control," said Hernandez, whose commute usually lasts just over an hour. "This is extremely abnormal."

There was the heat and the cursing and the honking and -- running through it all like the center line of an infinite highway -- the crushing, unending tedium.

"I hate this," grumbled Bahareh Madani, 27. "I just want to go home. How long is this going to go on?"

Yet many decided to make the best of things. A Starbucks manager in Franconia handed out Frappucino samples to weary commuters fleeing the gridlock. One woman bided her time in traffic by paying her bills and stacking them neatly in a tidy white box at her side.

Terri Fullerton, 29, a day-care worker at Franconia Baptist Church, took 2 1/2 hours to shuttle children in what would normally be a 20-minute trip, but the journey was lifted with song.

"We had a good old time," Fullerton said. "We played music and sang songs."

Others abandoned the crippled interstates altogether, as commuters became intrepid explorers searching for the best route to the West or, at least, to Woodbridge. Ron Anderson, a 51-year-old military cost analyst, pumped gas in Seven Corners as he mapped out a circuitous route that would take him from Route 50 to Route 123 to Interstate 66 to the Fairfax County Parkway and beyond.

"We're taking a new route we've never taken before," said Anderson, gripping the steering wheel of his Dodge Intrepid before heading out into the concrete jungle. "We have no idea how it will turn out."

Nor did the Coopers, the Fort Washington couple who were about to become parents of a third child as they inched among a tide of seething commuters toward Bethesda.

Wesley Cooper made a flurry of calls to relatives, friends and 911 on his cellular telephone in a feeble attempt to get help. Then Venita Cooper's water broke.

"Stop driving and get over here and catch this baby!" she said.

He pulled to the left and obliged, helping to deliver a lustily wailing eight-pound girl.

The mother said emergency officials, hindered by traffic themselves, arrived about 20 minutes later; no one stopped to offer aid in the interim.

"She just fell asleep and we waited," Cooper said. "It seemed like forever."

Her name, by the way, is Raina Alexis Cooper, and her commuter worries have already begun.

Staff writers Lyndsey Layton, Allan Lengel, Alice Reid, Eric L. Wee and Graeme Zielinski contributed to this report.

CAPTION: Yvonne Woods, left, is trying to get from Springfield to Tysons Corner, after a truck accident crippled the region's highways. She gets help from Sherry Roberson.

CAPTION: Southbound traffic backs up along Interstate 95 as thousands of motorists find themselves trapped by the overturned truck, which was carrying blasting powder.

CAPTION: Rosario Hodges sells bottled water at Ferndale Street and Braddock Road, near the Springfield interchange, where a truck loaded with blasting powder overturned.