What city staff called the "most expensive and difficult portion" of the long-anticipated Petaluma River Trail has been completed, providing a key link for bicyclists and pedestrians between east and west Petaluma.

The River Trail is a component of the Bicycle and Pedestrian Plan, which was finished in 2008 and calls for the creation of bicycle and pedestrian routes throughout Petaluma — and for some existing routes to be connected.

The recently completed portion consists of a 142-foot bicycle and pedestrian bridge and ramps that connect it to existing trails on either side. The bridge now provides safe passage from the east side of town to the west — across the Petaluma River to North Water Street. From there, pedestrians and bicyclists can connect to downtown, the city's waterfront and the Petaluma River Trail.

The bridge itself was installed on Feb. 21, as a crowd of bicycle and river enthusiasts watched on, and work continued after that to connect the bridge to ground level with ADA-compliant walkways and ramps.

All told, the project cost a little under $1.8 million, with construction totaling about $1 million. Most of the funds came from the quarter-cent sales tax Measure M, which was approved by Sonoma County voters in 2004. In addition to the bridge, a portion of the funds was allocated to other locations to create lighted crosswalks with pedestrian warning signals, railroad crossing safety barriers, wayfaring signs and other safety improvements.

It's now part of about 20 completed miles of off-road bicycle and pedestrian trail that weaves throughout Petaluma.

However, gaps still remain in the river trail. One is at Lakeville Street, where the trail ends at the water, creating a missing link between the Petaluma River Trail and the Lynch Creek Trail, which takes bicyclists and pedestrians to east Petaluma. The city must wait for the Army Corps of Engineers to build a retaining wall as part of the roughly $40 million flood control project before it can finish the trail there.

Caleb Conn, project manager for the Army Corps, said the entire flood project is 95 percent complete, with only a 30-foot and 70-foot retaining wall, one on each side of the river near Lakeville Street, unfinished. The Army Corps is currently designing those walls and hopes to have the designs completed by the end of 2013. However, funding for the roughly $2 million project is uncertain, as it is dependent on Congress allocating more money to the cash-strapped agency.

Currently, bicyclists and pedestrians using the trail must seek longer, alternate routes to connect the two parts of the trail.

For a long time, city engineer Larry Zimmer said, the city waited for the Army Corps to build the flood wall; but after it was repeatedly delayed, the city decided to move forward with Measure M funding and built the parts of the trail that it could.

Another missing component of the River Trail is construction of a path that would extend from where the trail currently ends on the west side of the Copeland Crossing Bridge, along the river, to Washington Street. Doing so will require paying nearby property owners for public access easements. That segment has yet to be funded, though there could potentially be leftover monies from Measure M available to the city. It is unclear how much that component of the project will cost, but Zimmer said it will be far less expensive than the bridge component was.

(Contact Jamie Hansen at jamie.hansen@arguscourier.com.)