Boise police have handed out only a handful of tickets since an ordinance went into effect in 2010 requiring motorists to provide at least three feet of room on the side as they approach and pass bicyclists.
On Thursday, police stopped six motorists and bicyclists for violations during a two-hour period on North 15th Street between Fort Street and Hill Road.
The police department set up the spot-check to see whether motorists were following the rule - enacted in response to some deaths from car-bicycle crashes - and whether bicyclists were staying within marked bike lanes.
It's not expected to become a regular occurrence, but police spokeswoman Lynn Hightower said other checks could take place this year if it appears there are problems.
Two bicycle officers rode in a loop, observing behavior by motorists and fellow bicyclists. They called for assistance from motorcycle officers stationed near Washington Elementary School to pull over faster-moving vehicles.
Andy Johnson, one of the bicycle officers, stopped a woman riding two abreast with another cyclist. The woman kept moving outside of a marked bicycle lane. Bicyclists are required to remain within a bike lane when one is provided.
The woman was friendly, gesturing to people she saw, Johnson said.
"She was waving and weaving," he said.
The woman was given a warning. Her companion remained in the bicycle lane and did not commit a violation, he said.
Johnson later watched as a man riding a mountain bike north on 15th pulled out of the bike lane and into the path of a pickup, whose driver honked.
"He admitted he came out of the lane and heard the driver honk," Johnson said, shaking his head.
He, too, was given a warning.
Another driver was pulled over when she went around a vehicle waiting for oncoming traffic to clear before turning left. In going around that vehicle, the driver swerved into the bike lane, which is a violation.
"She received a $90 citation for improper passing on the right," Johnson said.
In that situation, passing on the right is legal as long as the driver doesn't cross into a bike lane or go onto an unpaved section of the roadway.
Another motorist received a warning for crowding one of the bicycle officers, coming closer than three feet.
Two other drivers were pulled over for speeding. They received warnings for that but were cited when they could not prove they had auto insurance.
During the two-hour test, the vast majority of drivers complied with the law.
"My observation was that drivers were very conscientious of the three-foot bike lane," said Officer Blake Slater, the other officer on Wednesday's patrol.
John Sowell: 377-6423, Twitter: @IDS_Sowell