When it comes to moving cargo, delivering shipments by bicycle is about as green as it gets. That's one reason why "workbikes" with integrated cargo trailers that can carry loads of up to 1,000 pounds are gaining converts in eco-conscious cities like Boston, New York City, and Berkeley, Calif.

In Boston, for instance, The New Amsterdam Project uses the bikes to make urban deliveries for clients like Harvard University and an array of food manufacturers, including several whose products require refrigeration. Revolution Rickshaws in New York City says on its Web site that its "giant trikes" can race through the streets of Manhattan regardless of traffic conditions. Berkeley's Pedal Express, which is part of a loose network of bike services in college towns, counts several city governments, book publishers, and a lighting manufacturer among its clients.

Why bicycles? If you've ever watched a tractor-trailer or straight truck inch through crowded urban streets and then try to back into a downtown loading dock on a weekday, you already know the answer. In congested city centers, bicycles are faster, quieter, more maneuverable, and cheaper to operate than traditional trucks. And these days, transportation that requires no fossil fuel and emits no pollutants is extremely attractive from both a cost and an environmental standpoint.