Last summer, when south Palo Alto residents asked that a test of restriped traffic lanes on Arastradero Road be studied for another year, the city agreed. On Wednesday, the plan to permanently turn the street's four lanes to three lanes and add shared left-turn lanes and other improvements got the approval of the city's Planning and Transportation Commission -- with one caveat.

Commissioners voted 5-0 to recommend the project to the City Council, with Commissioner Samir Tuma absent. Commonly known as the Arastradero Road Re-striping Trial Project, the changes are aimed at slowing down traffic and making the road safer for pedestrians and bicyclists.

But the repercussions of changes to the major thoroughfare -- problems that prompted last year's extension of the trial -- remained on the mind of at least one commissioner.

Commissioner Mark Michael said he felt the study did not fully address traffic cutting through neighborhoods along Arastradero. He voted for the project only after receiving assurances from city staff members that they would study the issue, which residents said has increased hazards in the Barron Park neighborhood since the project began.

The Arastradero restriping constitutes the second phase of restriping and traffic signal changes along the Charleston-Arastradero corridor, which stretches from Foothill Expressway to Fabian Way. The corridor serves 11 public and private elementary, middle and high schools; multiple preschools; three community centers; and six parks. It leads to Stanford Research Park. New development, including at least 900 new homes, has caused congestion during commute hours and speeding at other times, residents have said.

The council approved changes for the Charleston Road portion in 2008 after a two-year study; the Arastradero portion has been studied since 2010.

The Arastradero changes include the lane reductions; the addition of a median, speed-reminder signs and traffic signals; restrictions on left turns during certain hours; and modification and coordination of signal timing at certain intersections.

Excessive speeding and accidents along the route have decreased by half as a result of the trial, city staff reported. But traffic volume rose in three areas within the Barron Park neighborhood: Maybell Avenue and Maybell Court; Maybell Avenue and Pena Court; and Matadero Avenue at Josina Court. The traffic count at Maybell and Pena rose significantly from 2,700 vehicles to 3,348 daily since the trial changes, according to the study.

Residents told the commission Wednesday that drivers are creating unsafe conditions along neighborhood streets that do not have sidewalks, endangering pedestrians and cyclists who must be in the road.

Chief Transportation Official Jaime Rodriguez admitted a speed survey had not been done along the cut-through routes. But he attributed increases to a 5 percent overall jump in traffic throughout the city.

Michael did not seem convinced by the staff explanation.

"There's something going on here with this cut-through on Maybell (Avenue) that's not really reflected in what we see here," he said of the study.

He said he was tempted to add an amendment to the commission vote to require a neighborhood-traffic survey, which would extend the road test for several months. He asked Rodriguez to commit to a study without the formal amendment.

Rodriguez agreed, saying it would be part of an analysis completed for the city's Pedestrian and Bicycle Master Plan. He has already recommended that the bike-boulevard design along Maybell Avenue be accelerated because it already functions as a bicycle boulevard, he said.

Commissioner Greg Tanaka said Maybell Avenue has three speed tables and two stop signs to slow traffic, and he asked about what other measures could be added to slow traffic down. Rodriguez said a combination of speed bumps and striping might be part of a design.

But it wasn't just diverted traffic that some residents said they disliked about the Arastradero plan.

Resident Joseph Hirsch's morning commute along Arastradero has gone from about 10 minutes to at least 20, he said. He asked that the changes not be approved until there are improvements along El Camino Real, which city staff have pointed to as causing backups along Charleston-Arastradero. The California Department of Transportation (Caltrans) is in charge of El Camino, and any design improvements to the state highway are under Caltrans' authority, however.

Barbara Freeman, a Donald Drive resident since 1982, said she does not feel safe crossing Arastradero now. Moving traffic through more consistently has not improved pedestrian safety, she said.

"Traffic used to go like schools of fish. Now it's like one unrelenting freight train," she said.

Some residents said the trial has accomplished its goals, chief of which is to improve safety. They pointed to the reduced number of accidents the study showed, both for vehicles and bicyclists and pedestrians.

"We must remember the purpose of this trial period," said Betty Lum, a Suzanne Drive resident since 1965.

Nina Bell told the commission she supports the changes, particularly the addition of shared left-turn lanes.

"With the center turn lane, I no longer have to wait in fear of someone rear-ending me when they come up from behind," she said.

Elizabeth Alexis said the study showed a 50 percent reduction in fast-vehicle speeds, which were above 37 mph.

"Slowing cars saves lives. If you are hit at 35 mph, you are probably dead," she said, citing studies.

Commissioner Eduardo Martinez said he was struck by the polarization among residents.

"I'm hoping that we see the value of what the city has attempted to do ... and that the city will continue to do" to ensure the safety of schoolchildren, he said.

Commissioner Arthur Keller agreed.

"Arastradero Road prior to the trial was a raceway. A four-lane street without left-turn lanes is simply not acceptable. I think there's enough improvement in the trial to move forward with this," he said.

The commissioners asked staff to work with the police department to increase enforcement along Arastradero and in Barron Park on Maybell Avenue and Matadero, where residents complained of speeding.

"It makes sense to increase law enforcement, particularly focusing in the beginning of the school year," Keller said.