New Yorkers can expect a slightly greener city Friday as 20 curbside parking spaces are converted into little "pocket parks." The idea is to make New Yorkers rethink the best use of the city's public space."Less than half of NYC households even own cars, and yet we give over so much road space to parking them," said Paul Steely White, executive director of Transportation Alternatives, which is building some of the local pocket parks.Similar parks will be open Friday nationwide, in an effort coordinated by the Trust for Public Land and dubbed "PARK(ing) Day."Similar to the park built near Penn Station last year, other pocket parks will sprout today near the MoMA, Lincoln Center, Park Slope and other locations citywide.See http://www.openplans.org/projects/park-ing-day for a complete list.