The I-370/I-270 interchange overlaid on Bethesda’s Woodmont Triangle.

In March, The Straight Line showed the difference in scale between urban development and the infrastructure underlying suburban development by overlaying the I-270/I-370 interchange on top of Bethesda’s Woodmont Triangle area.

The amount of space we devote to moving cars is almost surreal at times. At Montrose Road, Interstate 270 is a whopping 14 lanes wide. At that rate, it seems we’re trying to rival places like Atlanta and Los Angeles.

But what is even more amazing is the amount of space we devote to storing cars. When people think of the automobile, it is invariably involved in going somewhere. But cars spend the vast majority of their time parked.

In Montgomery County, about 2.5% of the land area is devoted to parking. That’s more than 12 square miles. It’s slightly less than the amount of land covered by water in the county. Can you imagine the Potomac River, and the Triadelphia, Rocky Gorge, and Little Seneca reservoirs all covered in parking lots?

Perhaps more shocking is that the amount of space devoted to parking and driving exceeds the amount of land devoted to all buildings in Montgomery County.

Buildings cover about 4.1% of the county’s land. But roadways cover 4.3%, meaning that we use 6.8% of the area of the county just to move or store automobiles.

Silver Spring is one of Montgomery County’s urban areas. There we find that 21.9% of the land area of the Central Business District is devoted to parking cars. Most of that area is surface parking. Only 3.8% of the land area of the CBD is used for structured parking. Another 16% of the land area is used for roadways.

In fact, four times as much area is devoted to surface parking than is devoted to parks in the Silver Spring CBD. Author’s note, added to clarify: This number only counts parks in public ownership. Privately held plazas are not shown because their surface area was not available at the time this calculation was done. These areas, like the Discovery Building’s Sensory Garden and the splash fountain on Ellsworth Drive are vital, vibrant spaces which add immeasurable value to Silver Spring. Again, they were not included because the data was not available. I apologize if this caused any confusion or consternation.

In White Flint, along the suburban Rockville Pike corridor, the numbers are even more extreme. I used the boundaries of the recent sector plan area to calculate the percentages.

There, some 45.9% of the land area is devoted to parking. Another 13.2% is devoted to roadways, meaning that 59.1% of the land area of the neighborhood is given over to cars.

Here, the lack of a parking lot district makes shared parking much more difficult. And that means that each business is providing more spaces than would be needed in a “park once” district.

All told, approximately 34.6 square miles of land area in Montgomery County is devoted to automotive transportation. If all the roads and parking areas in Montgomery County were placed in Arlington County, Virginia, they would completely fill Arlington, and there would still be 10 square miles of parking and roads left over. Or, placed in Washington, they would cover over half of the land area in the District.

Accommodating this sea of parking places a huge cost on both the public and private sectors. And it also has a major impact on the environment. But perhaps most notable is the opportunity cost of using valuable land in activity centers for parking. In White Flint, despite the presence of a Metro station, 45.9% of the land area is devoted to parking. Only 17.7% of the land is used for buildings!

As the county grows more dense, the acres of parking in places like White Flint are becoming more valuable as potential sites for redevelopment. How the parking issue is addressed will have an enormous impact on the future of the county.

Crossposted at The Straight Line.