Arlington County, Va., is the safest county in the U.S. for driving, and La Paz County, Ariz., is the deadliest, according to an Auto Insurance Center analysis of federal crash data from the past two decades.

The other nine counties cracking the top 10 list of safest counties are, in order, Bethel Census Area, Alaska; Broomfield County, Colo.; Bronx County, N.Y.; New York County, N.Y.; Kings County, N.Y.; Middlesex County, Mass.; Suffolk County, Mass.; Bristol County, R.I.; and Hennepin County, Minn.

At the other end of the spectrum, the nine counties joining La Paz County on Auto Insurance Center’s list of most dangerous counties are, in order, Tunica County, Miss.; Lowndes County, Ala.; Leon County, Texas; Big Horn County, Mont; Reeves County, Texas; Millard County, Utah; Emery County, Utah; Conecuh County, Ala.; and Jasper County, S.C.

The rankings are dependent on the number of fatal crashes per 10,000 residents.

“To pinpoint which states and counties are the safest and most dangerous for drivers, we analyzed more than 777,000 fatal accident records in the last 20 years from the National Highway Traffic Safety Administration’s Fatality Analysis Reporting System (FARS),” the Auto Insurance Center said in the online report.

Using the same criteria for states, the center determined that the five safest states are, in order: Massachusetts, District of Columbia (we know, technically not a state), New York, Rhode Island and New Jersey. The most dangerous states are, in order: Mississippi, Wyoming, Montana, Alabama and South Carolina.

What makes some states so much safer than others, based on the given criteria?

“Good public transportation is one feature that may play a role,” the Auto Insurance Center said. “Another factor may be the default speed limit on major highways in each state. The Northeast typically enforces top speeds of 55 or 65 miles per hour on urban and rural interstates respectively, while states in the South and West generally enforce top speeds of 70 to 75 miles per hour.”

Additionally, rural states such as Wyoming have many long stretches of two-lane roads that are seldom patrolled by law enforcement, the center pointed out. Many drivers exceed the speed limit as a result.

For additional data analysis by the Auto Insurance Center, click here.