The projected costs of a pedestrian and bicycle bridge spanning Highway 101 between Santa Rosa Junior College and Coddingtown mall have soared to as much as $20 million, more than double original estimates.

The new projections may be a significant factor in the Santa Rosa City Council's decision tonight about whether to move forward with the project, long sought by the city's cycling community.

Councilman Gary Wysocky, an avid cyclist, said the project would be an important way to link the college, a key retail shopping area, and the likely future location of the northern Santa Rosa SMART rail station.

"A pedestrian and bicycle bridge connecting to a light rail station – you show me a greener project in America," Wysocky said.

In 2009, when the city first held community meetings on the project, initial estimates ranged from $5 million to $9 million. The city then commissioned a just-completed feasibility study that put the numbers between $10 million and $14 million.

But a city staff report before the council Tuesday notes that the "full cost to deliver a complete bridge project could be closer to $20 million."

That's due to a number of "unknown costs" that could be associated with getting people to and from the bridge, such as bike and walking paths and signs, and higher potential construction costs if funding challenges delay the project further, according to the report.

The bulk of the construction costs would be paid for from federal transportation dollars but application for that money can't happen until a project is designed.

The council is being asked to sign off on the feasibility study and to approve the use of $100,000 of redevelopment dollars to fund a new study with Caltrans, which has freeway responsibility.

Even if all the money were available and all government agencies signed off on it, the project construction isn't likely to begin for a least two or three years, said Otto Bertolero, a civil engineer in the city's public works department.

One of the key reasons for the higher cost is that the goal is to have a bridge that is wide enough – 15.5 feet – to accommodate pedestrians and cyclists passing one another, Bertolero said. It also needs to have long enough approaches to allow for a gradual slope.

"To make it a usable facility, the approaches to the bridge became longer so you wouldn't feel like you had a mountain to go over," Bertolero said.

The 200-page, $117,000 feasibility study by the Berkeley-based Steven Grover & Associates envisions a curvaceous suspension bridge crossing the highway at different locations from the college to the west side. Models of the various bridge options contained in the study will be on display at the council meeting, and Steven Grover will give a presentation to the council.

While the design and location of the bridge are yet to be determined, city staff is recommending the northernmost option linking Elliott Avenue on the east side with Coddingtown mall on the west. Despite being a more challenging building site because of existing buildings, the northern option is preferred because it's closer to the likely future SMART station at Guerneville Road, Bertolero said.

But it also adds to the cost. The estimate for the southern crossing, at Bear Cub Way, was pegged at $10 million, but the northern option came in a $13.3 million.

Because the alignment and design of the structure have yet to be determined, however, the cost figures at this point are rough estimates, Bertolero said.

"These could be very far off. We just don't know until we get further into the design," he said.

Wysocky questioned whether the $20 million estimate is reasonable given the feasibility report showing the average construction cost of several bridges built in recent years around the Bay Area was $8 million, $10.6 million when additional "soft costs" were factored in.

The soft costs for a project like this are going to be at the "high end" because the there is dense development on both sides of the proposed bridge, Grover said. There are also high voltage power lines and a freeway sign that would need to be moved, he said.

Whatever the cost, Wysocky said it is important to put it in the context of automobile-focused infrastructure projects, like the $6 million widening of Santa Rosa Avenue at Kawana Springs Road or the $31 million parking garage at Santa Rosa Junior College.

"I'm not wild about spending all this cash, but when you compare it to other transportation infrastructure projects, then you get a sense of scale," Wysocky said.

The junior college set aside $1 million for the freeway overcrossing as part of settling a 2004 lawsuit over the multi-story parking garage in front of Bailey Field. The money comes from a $251 million bond measure approved by Sonoma County voters in 2002. The junior college's offer is only good through 2012.

The feasibility study can be viewed at http://ci.santa-rosa.ca.us/doclib/agendas_packets_minutes/Pages/20101130_CC_agenda.aspx.