Last week's answer

Question: In 1922, property owners along a steep, one-block section of Lombard Street in San Francisco faced a major problem: the natural 27% grade was far too steep for most automobiles of the era to climb or descend safely. To solve this, property owner Carl Henry proposed transforming the straight road into a series of eight sharp switchbacks. By adding these S-curves, what did engineers reduce the roadway's effective slope down to?

Answer: 16% grade

Considered the "crookedest street in the world," Lombard Street utilizes eight hairpin turns on San Francisco's Russian Hill to reduce the grade to a drivable 16 degrees.   

Sources: ABC 10