Cycling enthusiasts tend to be a passionate bunch. So it is not surprising that there are lots of questions about biking information on Google Maps forums. One group, called googlemapsbikethere.org, has collected more than 51,000 signatures asking Google to add biking directions to its maps.

On Wednesday, the company is answering the call, offering biking routes in 150 American cities in Google Maps. Google plans to unveil the service during the National Bike Summit in Washington. The event will be followed by a group ride at the South by Southwest festival in Austin, Tex.

Bicycling advocates are, not surprisingly, enthused.

“We think this is fantastic,” said D.L. Byron, publisher of BikeHugger.com, a blog about bike culture based in Seattle. “It will open up reliable transportation options to cyclists.” Mr. Byron said that while plenty of programs allow cyclists to upload their routes to the Web, no other service provides optimal directions for cyclists in urban settings, at least not on a national scale.

Mr. Byron predicted that the Google service would help to promote cycling as an alternative mode of transportation. “A lot of people would love to get on their bike but are afraid they won’t find a safe route,” he said. “If you make these options more available to people, they will do it.”

Much like the driving and walking directions on Google Maps, the service selects a route and calculates estimated cycling times after a user provides start and end points. The routing algorithm attempts to select optimal directions that avoid freeways and busy roads and intersections, and take into account bike paths, bike lanes and bike-friendly streets. They will seek to route around hills, whenever practical. Google Maps will also offer a “view” geared for cyclists that will display bike-friendly routes. A mobile version is likely to follow soon, said Shannon Guymon, a product manager for Google Maps Directions.

“We feel pretty good about our routing model,” Ms. Guymon said. But Google expects to use input from users to help improve suggested routes over time, she said.

Google has teamed up with the Rails-to-Trails Conservancy, a nonprofit that creates networks of trails from former rail lines, to obtain information on bike trails in more than 150 cities.

As for cycling times, Ms. Guymon said the estimates are “conservative.” “If you are in good shape, you are going to beat these times,” she said.

In San Francisco, the route from Dolores Park to the Golden Gate Bridge, through the Golden Gate Park Panhandle and along Masonic Avenue, suggests about 40 minutes. Any riders who can do better?