An avenue can be a dual carriageway road, or a straight road. It can be a tree-lined walkway that's off limits to normal vehicular traffic or a small and narrow side street. Sometimes it trains the eye toward a view in the distance. Engineer Pierre L'Enfant, who laid out the plan for Washington D.C., imagined the city as a grid of great avenues lined with trees and gardens. Now many of Washington's most important streets are called avenues. Paris' Champs-Élysées, a straight road edged with trees with a view to the Arc de Triomphe, is designated as an avenue, though it's sometimes thought of as a boulevard as well. In Manhattan, New York, avenues generally run north-south, and streets run east-west.
A boulevard is usually a multi-lane road with a median. It often has side streets. There's usually more landscaping around a boulevard than on an avenue or a regular street. There are few boulevards in Manhattan--Cabrini Boulevard in the upper part of the borough is a rare example. Broadway and Park Avenues, which are wide dual carriageways with medians for much of their lengths, might qualify as boulevards but aren't called such; however, New York's outer boroughs, especially Queens, are full of long boulevards, including Queens Boulevard, Woodhaven Boulevard, Northern Boulevard and Cross Bay Boulevard. Queens Boulevard is a 12-lane road with a median and service roads.
Boulevards appeared around the time of the Renaissance after the discovery of the principles of perspective. City planners began to build wide streets with views and formal landscaping. The Champs-Élysées, for example, was created in the 17th century.
The importance given to boulevards by city planners has made some of them world famous. Among them are the Strip in Las Vegas, the Paseo de la Reforma in Mexico City and the many boulevards of Los Angeles, including Sunset and Hollywood Boulevards.
