SOUTH PORTLAND — The battle over angled parking along a disputed one-way section of downtown Ocean Street took an unexpected turn over the weekend when Knightville residents informed city officials that angled parking isn’t allowed under city ordinances.

Nearly four years after the one-way section between D and E streets was established as part of a road and sewerage improvement project, it turns out that the City Council violated city ordinances when it haggled over and ultimately allowed angled parking on the block.

News of the ordinance oversight, coming on the threshold of a council workshop on the matter Monday evening, has upset some neighbors who have been pushing the city to undo the one-way because they say it has increased traffic on residential side streets.

“It’s a game changer,” said Melanie Wiker, a D Street homeowner and member of the city’s ad hoc Knightville Traffic Committee. “I’m just floored that the city isn’t following its own ordinances.”

The 15 angled parking spaces, included in the road project at the urging of a few businesses, made it necessary to reduce the two-way street to one-way traffic for one block in the up-and-coming neighborhood.

City motor vehicle and traffic ordinances passed in 1966 require parallel parking on city streets and specifically prohibit “diagonal” or angled parking.

Why city officials ignored the ordinances is unclear. Before the one-way section was built, Sebago Technics, a South Portland engineering firm, warned in writing that angled parking was prohibited.

“We assume the City Council must amend the ordinances to allow installation of (angled) parking,” Daniel Riley, project manager at Sebago Technics, wrote on Feb. 13, 2012, in a three-page memo on the planned road project.

The recent ordinance epiphany comes as the council is scheduled to consider a compromise option to restore two-way traffic on Ocean Street at a 6:30 p.m. workshop Monday.

The option – which was endorsed by a majority of the Knightville Traffic Committee but which no one seemed to like very much – would convert the angled spaces to perpendicular or 90-degree spaces and replace several parallel parking spaces with a second travel lane.

Assistant City Manager Josh Reny posted a memo Friday with the workshop agenda that recommended against the perpendicular option based on several public safety and design concerns. Then on Saturday, City Manager Jim Gailey sent an email to councilors that essentially pulled the perpendicular option off the table and explained how they face the same choice they wrestled with four years ago.

“The council needs to decide and basically rewind to 2012,” Gailey said in a phone interview Saturday. “I don’t know how we ever got angled parking down there. It probably was an oversight by us. But we need to make it right.”

To do that, the council must either amend the ordinances to make angled parking legal or return the block to two-way traffic with parallel parking on both sides, Gailey said in his email to councilors. The road project initially called for parallel parking only and it would cost the city little to paint new striping.

Gailey noted that there had been angled parking on Ocean Street prior to the road project. He said it may have been introduced when the Maine Department of Transportation built the Casco Bay Bridge in the mid-1990s and traffic from Portland was diverted away from Ocean Street to Broadway.

The council preserved some angled parking to address the fears of some business owners who believed they would lose customers if they had fewer parking spaces near their storefronts, Gailey said.

In recent years, however, new residential and commercial development has increased the number of vehicles traveling in Knightville and the one-way section of Ocean Street has been shown to constrict the full disbursement of traffic, Gailey said in the interview.

Meanwhile, Melanie Wiker and other opponents of the one-way say there’s growing concern that the city has gone to great lengths to preserve angled street parking that not only is illegal, but also is aimed at businesses that have off-street parking behind their buildings.

“No property owner should be seen as better than others and be given special treatment,” Wiker said. “It’s mind-boggling to me that this has gone on as long as it has and that our city leaders seem to pick and choose what rules they follow.