With signs pointing to an ongoing rise in U.S. traffic injuries and deaths during the first six months of 2015, Moody’s is warning that the trend is credit negative for auto insurers.

Moody’s explained that increases in auto accident frequency and severity are credit negative because “they can have a significant negative effect on personal auto writers.”

Here’s why: about 79 percent of net premiums collected are used to pay claims and related legal expenses.

The ratings entity cites a number of data points to back up its “credit negative” assertion.

Moody’s, as part of a broad credit outlook report looking at various industry sectors, noted new data from the National Safety Council that could point to a major longer-term problem for U.S. carriers. According to the NSC, U.S. traffic deaths rose by about 14 percent in the first six months of 2015 versus the same period a year ago.

For U.S. auto insurers, the NSC data is the latest bad news but it is not the first. Moody’s said the trend is consistent with higher auto accidents reported by auto insurers starting in the 2014 fourth quarter, a reality that is pushing some auto insurers to raise rates.

Why are auto traffic deaths on the rise? Moody’s indirectly blames the improving U.S. economy, whose falling gas prices has led to more miles driven. The other issue, Moody’s said could be drivers’ increased use of handheld devices, higher fraud and higher speed limits in some states.

As well, consumers may report minor claims more frequently now as the use of leased vehicles continues to rise.

A hike in the number of accidents and their severity reverses several decades of slow declines, made possible, as Moody’s said, by everything from an aging population with a better driving record, to car safety improvements and tougher drunk driving laws.

Source: Moody’s