For someone making $21,000 a year, paying $500 a year for auto insurance can be a struggle. Yet low-income families across the country are paying about that much for minimum coverage, even with clean driving records, according to the Consumer Federation of America.

Researchers at the advocacy group found that the five largest auto insurers — Allstate, Farmers, GEICO, Progressive and State Farm — do not offer basic policies to safe drivers for less than $500 a year in more than one-third of the nation’s low-income areas.

“High insurance premiums act to deny [low-income] Americans economic opportunity and also help to explain why so many low-income drivers drive without insurance,” said Tom Feltner, CFA’s director of financial services and the principal author of the report, on a call with reporters Monday.

Feltner and his team analyzed 81,000 premium quotes from the insurers across Zip codes in 50 large urban regions, comparing minimum coverage in neighborhoods with median household incomes of less than $41,638. A majority of drivers in the lowest-income Zip codes earned less than $21,000 a year.

Nearly half of the 50 regions examined had at least one lower-income Zip code where annual premiums charged by the big five insurers exceeded $500, according to the report. In nine areas, including Detroit, Orlando and Baltimore, prices exceeded $500 in all lower-income Zip codes.

Baltimore resident Sharnette Streat, 45, pays Allstate $1,764 a year to insure her 2004 Ford Escape. The mother of three said she hasn’t had any points on her driver’s license in 10 years, yet she is unable to find a lower rate. To make matters worse, her annual premium went up $288 in August, adding strain to an already stretched budget.

The $855 she takes in every two weeks from her job has to cover her mortgage, insurance, groceries, utilities and medication for her high blood pressure. And with a door-to-door commute of 60 miles a day to get to her job at the Maryland State Comptroller’s Office in Annapolis, Streat estimates that she shells out at least $30 in gas every two days.

“When you add all of that up, it’s just hard to make ends meet,” Streat said. “Those points came off my license, and I haven’t had any problems since then. So, why do I have to pay so much?”

Allstate, along with Farmers, deferred all questions to the Insurance Information Institute. The trade group’s president, Robert Hartwig, said the price of auto insurance is determined by a number of factors tied to risk, including car usage, where the car is parked and credit history. Insurance in urban areas, he said, tends to cost more because of higher rates of theft and accidents and higher repair costs.

“Insurers offer policies at a price that reflect the risks of every given area and every category of driver,” Hartwig said. “If the driver fits the risks characteristics that would produce the lowest possible premium, then that driver will likely be offered that premium.”

Hartwig said the institute found that on average auto insurance accounts for less than 2 percent of median family income. He pointed to federal data that said the cost of auto insurance for Americans with the lowest incomes fell 14 percent between 2008 and 2012.

Janet Johnson, a 46-year-old mother of nine in Salisbury, Md., said it certainly doesn’t seem like premiums are getting cheaper. And with her $10-an-hour job installing computers, it’s certainly no easier for her to scrape together the $137.62 a month, or $1,651.44 a year, she pays State Farm to insure her 2001 Hundai Sonata.

State Farm did not respond to request for comment; neither did GEICO or Progressive.

“If they went by my income, there is no way I would have to pay as much as I do now,” said Johnson, who noted that she has no points on her license. “I’m just getting back into the workforce, and I need that car. But the insurance is taking a lot out of what I need to get by.”

Johnson is exactly the kind of person that the federation believes could benefit from the sort of program California offers to low-income, safe drivers. The state provides minimal liability coverage, averaging between $226 and $338 a year, to drivers who make under $55,000 annually, have cars worth less than $20,000 and have driven at least three years with a clean record. A handful of state legislatures, including the Maryland General Assembly, have begun studying whether a similar program could work in their state.

The federation is urging states to replicate California’s program, which provides enough coverage to fund claims without any subsidy. The group would also like the National Association of Insurance Commissioners to develop a model to help state insurance regulators track auto insurance costs for lower-income drivers.

The report is the eighth in a series of studies the federation has issued on the struggles that low-income families have finding affordable auto insurance. Using an example of coverage for a 30-year-old woman with a clean driving record, the latest study looked at quotes in different Zip codes. The hypothetical woman had a license for 14 years with no accidents or moving violations and was in the market for minimum required liability coverage on a 2000 Honda Civic.

Hartwig argues that the premise of the study doesn’t reflect the reality of “urban areas, where accident frequency rates are higher than they are in general.” He advises families who are unhappy with their insurance to shop around for a better rate.

But shopping around for a better premium is no guarantee that lower-income families will find an affordable rate, said Marty Schwartz, president and founder of Vehicles for Change, a nonprofit organization that repairs donated cars and sells them to low-income families for as little as $750. His staff helps clients map out a budget to make sure they can afford to maintain a car, but he said many families are left with little money after paying insurance.

“We work with folks that help our families find the lowest possible rate,” Schwartz said. “But our families all pay more for the car insurance than they do for the car, and they’re only carrying minimum coverage.”