No stopping, no standing, no parking, no kidding

""No Stopping, No Standing, No Parking, No Kidding." So reads a warning in Midtown Manhattan, one of many such creatively worded signs that went up under Mayor Ed Koch in the 1980s. The aim: to cure New Yorkers of the stubborn habit of idling curbside in restricted zones.

But drivers across the country will be familiar with the traditional versions of this admonition: a sign with a red or green border that prohibits standing or stopping in certain areas. What is the purpose of such regulations? In school zones and near bus stops, the rationale is straightforward: idling cars block the access of vehicles trying to get into a zone designed for picking up and dropping off people.

In other areas, the reason for a standing and stopping prohibition is less obvious. For example, a Staten Island woman recently got slapped with a $115 fine for parking outside her mother's house in a quiet residential suburb because of a new No Standing sign hidden among leafy trees. Why was it put there, on a perfectly wide street with ample parking? According to the Department of Transportation, the sign was intended to enhance safety by increasing visibility at the nearby intersection. Maintaining clear sightlines at intersections—apractice called "daylighting"--reduces risk of collisions.

In major cities, miles of curbside parking is often off-limits during rush hours. In Washington, D.C., for example, the block in front of the National Geographic Museum is lined with meters allowing two hours of parking. But no matter how much you feed the meter, don't stop your car there from 4:00 to 6:30 p.m.: in late afternoon, that parking zone becomes a travel lane. Signs prohibiting stopping, standing, and parking in morning and evening are common in commuter cities like D.C.; they have green borders, and often read along the lines of, "No Stopping, A.M. Rush Hour."

Other reasons why cities may prohibit stopping or standing in certain places include providing a buffer space for delivery trucks turning into commercial driveways or preventing blockages on a narrow street.

Sometimes, multiple signs regarding stopping and standing can create ambiguity. When this is the case—for example, a No Stopping 9 a.m. to 5 p.m. sign above a No Parking A.M. Rush Hour sign—always obey the most restrictive sign. We'll end with a caveat: given that it's extremely difficult, if not impossible, to park without stopping, these No Stopping signs also implicitly prohibit parking.