Google announced at the National Bike Summit in Washington, D.C., that bicycling directions for 150 U.S. cities including Los Angeles, San Francisco, Denver and New York City are now part of its map service. Previously, Google Maps was able to provide driving, walking or public transit directions. More than 12,000 miles of trails are now included in biking directions and outlined directly on maps through the service thanks to a partnership with the Rails-to-Trails Conservancy.

The service includes a time estimate for the route based on a complex set of variables including bike trails, bike lanes, recommended routes, uphill slopes, downhill slopes, busy roads and busy intersections. When users look for directions, the company's mapping algorithm weights trails more heavily than roads for safety reasons. If cities have bicycle lanes, those are also weighted more heavily than roads without them. Trails are indicated in dark green in the tool's bicycling layer. Streets with dedicated bicycle lanes, meanwhile, are marked in bright green, while recommended routes are shown with dashed green lines.

One of the neatest features built into the Google Maps bicycling tool is its power-exertion calculation. Biking directions take into account the effort bicyclists will require and the speed they will achieve while going uphill. Based on those calculations, the tool provides bicyclists with a route that eliminates areas that would require an unreasonable degree of exertion.

Google Maps has been one of Google's most successful products and the new bicycle tool has been one of the most requested features. Try it out at http://maps.google.com.

Other bicycle trail mapping systems include MapMyRide.com that ranks streets in five colors on riding suitability, based on the amount of interaction with traffic and RTC's TrailLink.com which includes more than 30,000 miles of bike trails, walking trails, equestrian trails, and hiking and running trails including interactive trail maps, trail descriptions, pictures and more. The inclusion of the Rails-to-Trails Conservancy (RTC) trail information in Google Maps comes at a time when people are clamoring for biking opportunities. In the last year, RTC has seen an unprecedented surge in its TrailLink.com users. RTC, a nonprofit membership organization headquartered in Washington, D.C., is working to create a nationwide network of trails from former rail lines and connecting corridors.