WASHINGTON (Map, News) - The heavy, steady rain that pounded the region for more than 24 hours sent rivers over their beds, destroyed homes and caused one Montgomery County woman, caught in the grip of Beltway traffic, to deliver her third child in the back of a car.

A little before 10 a.m. Monday, the woman, whose name was not released by a fire department spokesman, realized she didn’t have time to reach Holy Cross Hospital in Silver Spring. She and her husband pulled over near the New Hampshire Avenue exit on the Capital Beltway, called police and, while the husband spoke to a dispatcher, their baby girl was born. Mother and daughter are doing fine, the spokesman said.

The rising waters and falling trees caused thousands of power outages and closed about 90 roads throughout the region, including about 20 in suburban Maryland, 63 in Northern Virginia and seven in the District of Columbia.

Rescuers in Prince William County evacuated 31 homes and rescued more than 18 people from rushing water, mostly from vehicles trapped in flood zones.

In Prince George’s County, a sinkhole nearly swallowed a home, and county offices and the courthouse in Upper Marlboro were shut as water swamped the town.

“This is some of the worst flooding we’ve seen in at least 30 years,” Vernon Herron, Prince George’s director of homeland security, said from inside the county administration building where sandbags were placed to hold off the rising tide.

Torrential downpours brought up to 3 inches of rain and put most of the area under flood warnings and closed dozens of roads across Northern Virginia, flummoxing commuters and rural school systems, a shock that left Fauquier and Stafford students at home for a rare weather cancellation in May.

Floodwaters erased the earth under a section of Dale Boulevard in Dale City, leaving a 20-foot-deep hole in the four-lane Prince William County thoroughfare.

Authorities scrambled to keep traffic moving, weathering flood delays on the Metro near the King Street station in Alexandria and a washed-out exit ramp off Interstate 66 at Route 50 in Fairfax County.

“We’ve got a lot of roads closed, a lot of trees down and a lot of power lines out,” said Mike Salmon, a spokesman for Virginia’s Department of Transportation.