Nearly all developments in Seattle's urban centers will be required to build sidewalks, according to a piece of legislation announced by Mayor Greg Nickels on Thursday. His "Keeping the Pace" project proposes to fill the gaps in the approximately 500 miles of city streets that do not have full sidewalks.

"In order to combat global warming, we need to make our neighborhoods compact, and that means building more sidewalks," Nickels said.

The proposal requires developers to build sidewalks in all projects, regardless of size, built in urban centers and villages and along arterials. Single-family additions and remodels of over 500 square feet will also be required to build sidewalks.

Under current regulations, developers are exempted of building sidewalks for projects under six to 10 units, depending on the zone. Some developers skirt these regulations by building multiple projects under the threshold for sidewalk construction, Nickels said.

Requiring sidewalks only for new developments will result in a patchwork, Nickels acknowledged in response to a question. This proposal will supplement the 117 blocks of new sidewalk slated to be completed under the 2006 Bridging the Gap Levy.

"We'll identify areas with most vulnerability and most traffic and tick them off one by one, year after year," Nickels said. "We know that where seniors go do shopping, where kids go to school, these are priorities."

Since 2004, 90 blocks of sidewalk have been constructed in Seattle, and 100 additional blocks have been rehabilitated in the past five years by the Seattle Department of Transportation.

Paulo Nunes-Ueno, a member of the city's pedestrian master-plan advisory group, spoke in support of the proposal. He also said that the cost of providing these sidewalks, even over time, will be challenging.

"We need to find innovative ways to pay for the sidewalks," Nunes-Ueno said.

Under the Bridging the Gap levy, the city is already spending approximately $1 million a year building sidewalks. The city is looking into efficient, cost-effective building techniques, according to Nickels. One prospect is building sidewalks with natural drainage to circumvent the high cost of installing drainage.

Ref Lindmark, co-chairman of the citizen oversight committee for the Bridging the Gap levy, said that in his experience with Bridging the Gap, citizen call for sidewalks is strong.

"Everywhere we went people said: 'Before you fix the road, give me a sidewalk,'" Lindmark said. "This is a critical step."