DETROIT - People are waiting longer than they should for an answer when they petition the government to open an investigation into what could be serious safety problems.

The Associated Press reviewed all 15 petitions filed by drivers with the National Highway Traffic Safety Administration since 2010 and found the agency missed the legal deadline to grant or deny the requests 12 times. One petition from 2012 has yet to be resolved.

A 1974 law passed to make the agency move faster requires a decision within four months of receiving a petition. But even though the agency has fined automakers such as General Motors and Toyota millions for missing deadlines to disclose safety issues, there is no penalty when it's tardy itself.

NHTSA concedes it has missed the deadlines but says it often must ask petitioners for more data to complete its analysis. Still, in eight petitions reviewed by the AP, it took more than a year to open an investigation or close the case.

Safety advocates say a delay that long can put lives at risk. And given the recent criticism of the agency for its role in GM's delayed recall of cars with defective ignition switches, these advocates question whether it is functioning well enough to protect the public.

"Everything is just really slow," says Matt Oliver, executive director of the North Carolina Consumers Council, which petitioned the government in February 2012 on behalf of drivers seeking an investigation of Nissan truck transmission failures. It has yet to get a decision. "You have to ask is everything going as efficiently as it can?"

Car owners have two ways to ask safety regulators for action. They can file a complaint, or submit a petition. A complaint has information about a single incident and usually is filed via the agency's website. Petitions are formal requests for investigations, with evidence of a problem in many vehicles.

Often petitions are a last resort for drivers frustrated by intransigent automakers. Many drivers seek help from safety advocates to complete the petition. And even if an investigation is opened, it can take months or years before a recall is announced.

Clarence Ditlow, executive director of the Center For Auto Safety, a nonprofit founded by consumer advocate Ralph Nader, petitioned in November of 2009 for an investigation into fires in Jeep SUVs with gas tanks behind the rear axle. Despite reports of 12 fires, nine injuries and one death at the time, it took the agency more than nine months to grant the petition and open a formal investigation - five months after the legal deadline.

The agency's probe found 51 fire deaths as of last June, when a recall was finally announced. Ditlow says that since the petition was filed, at least 31 people died in fiery rear crashes involving the SUVs.

Chrysler, the maker of Jeeps, maintains the SUVs perform no worse than comparable vehicles. It agreed to install trailer hitches to protect the tanks in low-speed crashes.

Realistically, the agency may need more than 120 days for complex petitions, says former NHTSA administrator Joan Claybrook. Legislators should extend the deadlines and take funding from the agency or the administrator's salary if they aren't met, she says.

NHTSA has been criticized for failing to connect the dots among thousands of consumer complaints it received last decade about General Motors small cars with defective ignition switches. GM finally recalled the cars this year. The faulty switches have been linked to at least 13 deaths.

While GM withheld details of the problem from the public and the government for more than 10 years, critics say the safety agency still collected plenty of evidence to open an investigation and order a recall sooner. No petitions were filed in the GM case.

During hearings into the GM recall, some lawmakers suggested the agency's staff and budget are too small to monitor the 238 million cars and trucks on the road today. Plus, the agency regulates heavy trucks, buses, motorcycles, tires and auto parts. Its Office of Defects Investigation has only 50 investigators and a budget that's been about $10 million for a decade. By comparison, General Motors alone has at least 60 safety investigators.

NHTSA's investigation budget is only about 7 percent of the $134 million the agency spends per year on vehicle safety research, testing and enforcement. Sen. Claire McCaskill, D-Missouri, has introduced a bill that would double the $134 million over six years.

Petitioners often point out potential life-threatening problems that haven't been addressed by safety regulators. The North Carolina group, for instance, complained that coolant can leak and mix with transmission fluid in 2005-2010 Nissan Frontier, Xterra and Pathfinder trucks. That can cause the transmissions to fail.

The petition was filed after consumer complaints to Nissan went nowhere, Oliver says. In a statement, Nissan says the coolant leak is not a safety problem since it hasn't been tied to any injuries. The company extended the transmission warranty to 10 years or 100,000 miles, which it says addresses a customer satisfaction issue.

Since the filing, the group has received 500 to 600 complaints of similar problems. Oliver isn't aware of any injuries, but maintains that the agency's delay still risks lives because transmissions can fail on freeways, leaving people stuck amid heavy traffic.

"Anytime you have anything that will affect the safety of the vehicle, any kind of a delay on top of that is always going to put somebody at risk," he says.

Donald Friedman, co-founder of a California firm that investigates crashes for attorneys, filed a petition in November seeking an investigation into the air bag systems in big General Motors cars such as the Chevrolet Impala. Friedman says the passenger weight-sensing system in the cars can malfunction, causing the air bags not to inflate.

NHTSA has yet to make a decision.

In a statement, the safety agency denies dragging its feet on petitions such as Friedman's, saying it often needs more than 120 days to examine them thoroughly. "Most do not provide sufficient data for NHTSA to evaluate the issues raised without further data collection and analysis," the agency says.

Addressing consumer safety concerns in a timely manner is likely to be debated when agency chief David Friedman makes a second appearance in the fall before House and Senate subcommittees investigating the GM recall.

Sen. Edward Markey, D-Mass., said during a June hearing that NHTSA "shrugged" as evidence mounted that ignition switches were causing deaths in GM cars such as the Chevrolet Cobalt and Saturn Ion.