Portland's chamber of commerce still isn't convinced that Better Naito, which turns one lane of vehicle travel into a bike and pedestrian pathway, doesn't add to congestion despite a recent city analysis showing marginal effects for downtown drivers.

The Portland Business Alliance believes the city cherry-picks travel-time data to paint the project in a favorable light while not doing enough to evaluate the potential ripple effect on downtown congestion.

"We continue to be concerned about the impacts of Better Naito," said Marion Haynes, the Portland Business Alliance's vice president of external affairs. "And as we've evaluated some of the data that's been presented, we find that it lacks the type of thorough analysis that we would hope would occur on this project and others throughout the city."

Haynes said the Better Naito analysis raises questions about how the city will handle changes to major arterials elsewhere.

Portland transportation officials stand by the traffic analysis and point to a separate traffic survey commissioned by The Oregonian/OregonLive in 2016, which documented similar delays on the much-used road running along Waterfront Park.

"All of this analysis has consistently shown less than two minutes of delay for northbound drivers when Better Naito is in season," Dylan Rivera, transportation spokesman, said in an email.

Portland will once again convert one northbound lane of traffic between the Hawthorne and Steel bridges into a bike and pedestrian path starting May 1. The path will remain until Sept. 30 to coincide with the major festival season at Tom McCall Waterfront Park. The goal is to shift bikes from the path along the Willamette River to the Better Naito lane on the street, relieving dangerous congestion between pedestrians, joggers and cyclists on the path.

The city used "trained observers," pneumatic tube counters in the road and third-party 24-hour videos, to measure ridership. Those counting methods produced an average daily bike volume of 2,587 one-way trips, which the city used to estimate total ridership at 393,173 one-way rides during the 2017 season.

This would be the second time Portland converts the vehicle lane into a multi-use path for a five-month period. A volunteer group ran a smaller version of the travel project, which temporarily separates the pathway from the other northbound travel lane, in 2015 and 2016.

The city's report indicated travel times jumped by 1 minute and 28 seconds during the hours of 7 and 8 a.m., and 1 minute and 33 seconds from 4 to 5 p.m.

But chamber officials said those travel times were counted in an area from Southwest Clay Street to Stark Street. The Better Naito project areas stretches to Davis Street, another eight blocks north.

The Portland Business Alliance, which functions as the city's chamber of commerce, was skeptical enough of the city's analysis that it, along with the Building Owners and Managers Association of Oregon, hired a traffic consultant to review the city's data.

Sorin Garber & Associates determined the city's report was "incomplete." Transportation officials appeared not to look at longer lines backing up on Naito, nor the effect of traffic diverting onto other city streets to avoid the area.

The analysis also didn't examine travel times on adjacent streets or establish whether traffic was affected by the Morrison Bridge construction project or other developments in 2017.

"We hope to have better data collection, a more thorough data collection, so that the community can have a more thorough discussion about some of the tradeoffs and whether there are other alternatives," Haynes said.

Rivera said the business group shared the Sorin Garber report with city leaders. Transportation officials already continues to do "extensive analysis" of traffic volumes and times, he said.

Portland didn't look at the stretch of road from Stark to Davis because it didn't gather data from those areas during the first two years of the project. But Rivera pointed out The Oregonian study did look at that areas and found similar travel delays, and the city will analyze the entire stretch in its 2018 report.

The city didn't look at adjacent street congestion, Rivera said, because a 2015 report found "no diversion." Additionally, the traffic counters are in high demand elsewhere.

"Many of these suggested analyses would be quite costly, exceeding the cost of implementing Better Naito," he said.

Rivera added that traffic queues up on Naito because of train crossings on the Steel Bridge and drivers using the ramp to head east on the Hawthorne Bridge - not Better Naito.

The city plans a significant project to address the Hawthorne backup during weekday afternoons.

Large-scale work is scheduled to begin in 2019 on an estimated $6.7 million overhaul of the half-mile stretch of Naito from Interstate 405 to Jefferson Street.

The project includes grinding and repaving the road, adding a traffic light for merging onto the Hawthorne Bridge and constructing a separate bicycle greenway.

That project doesn't include extending the separated pathway north of the Hawthorne Bridge.

An unaddressed question is whether the city will make Better Naito permanent, an idea for which Rivera said the city has received vocal support.

Haynes said the business association is not against bike and pedestrian projects generally, or a separate pathway on Naito in particular.

"There needs to be additional discussion about whether there are alternatives to provide the kind of safe bike access that people clearly want, while not having undue impacts on other parts of the transportation system," she said.

Haynes called the bikeway project south of Hawthorne, which maintains two vehicle travel lanes, "kind of a win-win."

"We should be looking for those types of opportunities," she said.

Rivera said the city has looked at that option.

Cost estimates for making Better Naito permanent range from $4 million to more than $13 million. Keeping the second travel lane would the most expensive option, Rivera said, because the city would need to carve into Waterfront Park and work around existing street lights, utilities and traffic signals.

-- Andrew Theen

atheen@oregonian.com

503-294-4026

@andrewtheen