Playing catch-up with the dozens of U.S. cities that have expanded public transit with bicycle-sharing programs, Philadelphia finally is pushing off from the curb and heading out on the city's many bike lanes.

Mayor Nutter today is expected to announce deals to supply and operate a network of hundreds of heavyweight rental bikes like those working well in metropolitan areas nationwide. That, along with a Comcast-Spectacor subsidiary's effort to recruit sponsors, is a major step forward.

Officials plan to launch bike sharing in two phases next year and to eventually cover Center City and beyond. A happy by-product of the city's painfully deliberate pace in developing the program is that its design has benefited from other cities' experiences. The expected scale should assure that there are enough bikes and parking stations to make the system attractive to tourists, commuters, and residents alike.

Bike sharing is a natural for a city that has embraced cycling for recreation and, increasingly, commuting, as well as bike-friendly downtown living.

All in all, Nutter's vision appears deserving of public investment and anticipated foundation support. The challenge will be to deliver on his pledge to build a first-class bike-sharing system.