It may be commonplace in Washington, D.C., but in New York City, sharing a cab ride is still a rarity. That's changing with a new one-year pilot program that will allow up to four passengers to share a taxi along three routes in Manhattan for a discounted per-person flat fare of $3 to $4. The shared rides, which will pick up passengers at designated taxi stands and allow them to hop-off anywhere along the route, will only be active during morning rush hours. The routes were determined using GPS data, which picked out the most heavily-trafficked corridors. Officials say the experiment will increase taxi capacity during high-demand hours, reduce greenhouse gas emissions, cost passengers less, earn drivers more and make the practice of sharing cabs more economical and standard. If all goes well, the city's Taxi and Limousine Commission hopes to expand the program by having specially marked "ride share" yellow cabs driving around town.