A sudden rise in traffic deaths surprised big car insurers in the first half of 2015, meaning higher premiums for drivers who are now traveling in record numbers. Industry executives say the 14% surge in fatal accidents tracked by the nonprofit National Safety Council was due to a combination of factors: the lowest gas prices in years, adverse weather in some parts of the country, and an economic recovery in the U.S. that means drivers are driving more. The upsurge after years of declines was an unexpected development for two of the three largest car insurers, Geico and Allstate. Both are raising premiums to offset the expenses associated with the new accident claims. Allstate this year has gotten approval from dozens of states to boost rates by an average of 3.9% for its main product, according to financial filings and Geico said in its second-quarter earnings report that its implementing premium rate increases “as needed” to offset jumps in the frequency and severity of customer claims. Analysts say drivers could be facing a prolonged period of rising premiums. In an Aug. 26 report, Nomura stock analyst Clifford Gallant noted that while some insurers “are already reacting aggressively with rate increases, we expect that multiple rounds may be necessary just to catch current trend.” “More miles driven, more cars on the road, more accidents,” said Allstate Chief Executive Tom Wilson in an interview. Fatal crashes had been falling in the past decade because of more-frequent use of seat belts, tougher enforcement of drunk-driving laws and a proliferation of newer, safer cars with stability-control systems and air bags. Some of those trends contributed to a decline in car-insurance costs for consumers—the average annual expenditure for auto insurance in the U.S. crept down from $1,076 in 2003 to $846 in 2011, according to inflation-adjusted data from the National Association of Insurance Commissioners. The average expenditure has edged up 2% since then to an estimated $867 last year, according to trade group Insurance Information Institute. The increase is in part because Americans have gotten comfortable buying new cars again, and those cars are more expensive—and more costly to insure—than the ones they replaced. Roads turned more dangerous this year as travel increased 3.5% to a record 1.54 trillion miles through June, according to the Federal Highway Administration. Although population growth contributes to increased mileage, the number of miles Americans drove in recent years barely budged from a peak in 2007. That’s despite the population growing by 6.6% during the same period, according to a study by the Insurance Information Institute. Meanwhile, gas prices plunged to their lowest level since 2010, according to figures from the American Automobile Association. In addition, the unemployment rate has fallen to 5.1%, meaning more people are using their cars to get to work. It’s kind of a perfect storm as Motor-vehicle deaths are now expected to exceed 40,000 for the first time since 2007, according to NSC. Distracted driving, especially the use of smartphones to talk, text or even watch videos while on the road, could be an overlooked contributor. Not all insurers are seeing large increases in claims. Progressive Corp. Chief Executive Glenn Renwick said last month the increase in miles driven hadn’t translated into an uptick in claims.