With potholes, sinkholes, dips, cracks, years of patches on patches and entire blocks that can be navigated only by expertly executed turns, everyone knows New Orleans' streets are in bad shape.

So bad, in fact, that the average condition of all roads in the city rates less than 43 on a scale of 100, and nearly two-thirds of the streets are in "poor" or worse condition, according to a new study.

The report, compiled by a consulting firm that analyzed every block of every street in New Orleans over the past two years, paints a bleak picture of both the current state of the roads and the mammoth, multibillion-dollar effort that would be needed to bring them to acceptable standards.

The road survey, conducted by Stantec at a cost of about $555,000, represents the first comprehensive look at exactly how bad New Orleans' streets are. It will play a prominent role in the city's ongoing planning about how to fix the streets, including how to spend about $2 billion in FEMA money for road and drainage work in the coming decades.

Even that money represents only a portion of the $3.6 billion the report estimates would be needed to bring the streets to an average level of "fair" over the next 10 years — and to achieve that the city would need to do nearly all that work immediately.

That, the report notes, "would be essentially impossible to implement at one time without effectively shutting the city down. It does, however, present a representative picture of the challenges the city will face over the coming years and decades, as it attempts to renew its roadway infrastructure."

While there are a few billion dollars available, largely due to the FEMA settlement the city secured last year, officials say that will cover only a portion of the needed work.

More than 65 percent of the roads in the city were given grades of D or worse in the report, meaning they are in "poor" shape at best. And of those roads, two-thirds were graded as F, meaning they are in "very poor" or failing condition.

Just 14 percent of the city's streets were found to be in "good" or "excellent" condition.

"Everyone thinks their street is the worst, and probably for good reason," Deputy Mayor Ryan Berni said.

No area better than 'fair'

To produce the study, Stantec used vehicles equipped with sensors that determined how deteriorated a street was and calculated the quality of the ride for those driving over it.

That level of analysis has never been done before in the city, so there's little ability to compare current conditions with those in the past.

"Part of the reason for doing this now was to have a baseline, knowing that Katrina had a major impact on the streets," said Mark Jernigan, the city's director of public works.

The problem is citywide. While there are differences among areas, no neighborhood earned an average rating higher than "fair," and only five neighborhoods — City Park, B.W. Cooper, Desire, the Central Business District and West Lake Forest — attained even that score. Of those five, two are former public housing complexes that underwent wholesale demolition and redevelopment after Hurricane Katrina.

The city has not yet released street-by-street assessments in a form that can be analyzed, though it has promised more details and an interactive map on the city's website in about a month.

However, a look at the neighborhood ratings suggests bad conditions cut across demography and geography.

The Plum Orchard section of New Orleans East has the dubious distinction of having the worst roads in the city, but close behind are the Garden District, Uptown, East Carrollton and East Riverside. Audubon and the Lower 9th Ward, two sharply contrasting parts of the city economically, both received F ratings, two of 28 neighborhoods to receive a failing grade.

"Everyone is impatient (to fix the roads), most particularly the mayor. But this money is going to hit the streets over the next couple of years, and it's going to be on a larger scale and magnitude than even the SELA projects," Berni said, referring to the major, mostly Uptown drainage projects that have been under construction for years.

"But (with SELA) you're only talking about some major arteries that impacted several neighborhoods," he said. "In this instance, you're talking about full reconstruction of major parts of at least a quarter of the east bank neighborhoods, if not half, over a five-year time frame."

As city officials have grappled with the issue of crumbling streets, they've tied the repairs of roadways to fixing the damaged and leaky infrastructure below them. That would eliminate many problems that can lead to further roadway damage down the line, but it represents a lengthy and expensive process.

Just getting the roads up to decent condition, where the average New Orleans street would rate a C, will take spending $200 million to $350 million a year over two to three decades, according to city estimates. Over that span, another $30 million to $35 million a year will be needed to continue performing regular maintenance.

The city now spends about $150 million to $200 million a year on roadwork, about 10 times what was spent prior to Hurricane Katrina.

A scheduling challenge

The largest pot of money the city is working with is a FEMA settlement that totals about $2 billion for damage to water, sewerage and drainage systems during Hurricane Katrina and to the streets above them. The city has identified another $1 billion it can use, primarily from increases in sewer and water fees.

Rebuilding every street in the city to "good" condition is expected to cost about $10 billion. About half of that would be needed to fix just the streets that are in poor or worse condition.

How to stagger projects across the city and deciding which roads to fix when will be guided, in part, by the new study. But fixing the roadways isn't as easy as just starting with the worst ones and working up the scale.

Once a road falls too far into disrepair, the cost of fixing it can as much as quadruple as the job goes from fixing the surface to essentially digging it up and starting from scratch. That means money must be spent now to be sure streets that are in good condition remain in shape, even though others are in far greater disrepair.

"What we're looking at is sort of a hybrid model," Jernigan said.

The city plans to roll out more details of the report at a meeting Tuesday of the Fix My Streets Finance Working Group, which was convened by Mayor Mitch Landrieu last year to look at additional ways to fund street repairs. That's particularly important because the likelihood of any more major infusions of federal funds is virtually nil.

That group has yet to make any firm recommendations, though any proposals are likely to involve some sort of new taxes. Other possible sources of funding could come out of discussions at the state level of revamping Louisiana's system for paying for infrastructure improvements, such as a potential local gasoline tax.

The grimness of the new report could provide arguments for city officials as they negotiate with the state or try to win support for taxes from New Orleans voters.

"As the state is setting up long-term financial structures to drive more money for infrastructure — which we know is important for quality of life, is an important economic development tool and makes us stronger and more resilient — we know that local governments have to have a seat at that table," Berni said.

Follow Jeff Adelson on Twitter, @jadelson.​