Speeding car passing fatal traffic accident sign.

Motorists in Massachusetts and Washington DC can breathe easier on their afternoon commutes today. Their chances of dying in a traffic accident are the lowest in the nation. Drivers in West Virginia, South Carolina and North Dakota, on the other hand, may want to be especially vigilant. They're collectively navigating some of the deadliest roads in the United States.

Your odds of dying in a traffic accident depend a lot on where you live. Michael Sivak, a researcher at the University of Michigan's Transportation Research Institute, has analyzed federal traffic data, and found a wide disparity in the fatality rates across individual US states and the District of Columbia.

Washington D.C. and Massachusetts ranked first and second in both lists of the safest states.

The data can be parsed two ways, either by measuring deaths per distance driven or the number of deaths measured relative to state population.

Measuring in terms of vehicle miles traveled, West Virginia has the highest fatality rate in the nation. It has a rate of 17.63 deaths per billion vehicle miles traveled, more than four times the rate of deaths found in the District of Columbia, where there are only 4.2 deaths per billion vehicle miles traveled. The national average is 11.3 fatalities per billion vehicle miles traveled.

Measuring in terms of death per population, there's even more of a disparity between the safest and most dangerous states. Washington DC has a fatality rate of 2.37 per 100,000 people. Residents in the worst state, North Dakota, are more than 10 times more likely to die, with a per-100,000-population rate of 24.3. (By population, the national average is 10.69 deaths per 100,000).

Overall, residents of the Northern Plains states and South have the worst fatality rates. Washington DC and Massachusetts ranked first and second in both lists of the safest states, and Minnesota, Connecticut, Washington, New Jersey and California all were among the top 10 on both lists. Among the most dangerous states, Oklahoma, Mississippi, North Dakota, West Virginia, South Carolina and Montana all ranked in the bottom 10 on both lists.

There are differences between the two lists, but the general results are similar: the safest states rank high on either list, and the more dangerous states fall toward the bottom in both cases.

Several factors shape the fatality rates, though Sivak cautions he has not attempted to discern their influences in this study. Generally speaking, "you can look at what speed limits are there, what kind of topography," he said. "What is the proportion of urban versus rural? What are the alcohol-enforcement policies? What is the age distribution of drivers? It goes on and on."

Dangers posed by rural roads can be especially acute. The consequence of a collision at high speeds, of course, are much greater than at lower city speeds, and factors like alcohol use, reduced visibility and drowsy driving can differ along urban-rural lines. Response time from emergency workers can also be longer.

Though there are many less vehicle miles traveled overall on rural roads, which are defined by specific population and density standards set by the Federal Highway Administration, they were home to 54 percent of traffic deaths in 2012, according to the National Highway Traffic Safety Administration statistics.

Where does your state rank? Click through to see.
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Fatality rates per billion vehicle miles traveled
(Source: Michael Sivak, University of Michigan)
1. Washington D.C. 4.20
2. Massachusetts 6.24
3. Minnesota 6.93
4. Connecticut 7.55
5. Washington 7.82
6. New Jersey 7.94
7. Utah 8.18
8. Rhode Island 8.20
9. New Hampshire 8.38
10. California 8.76
11. Maryland 8.94
12. New York 9.11
13. Illinois 9.14
14. Virginia 9.60
15. Indiana 9.87
16. Michigan 9.92
17. Ohio 9.96
18. Colorado 10.09
19. Oregon 10.13
20. Wisconsin 10.41
21. Vermont 10.67
22. Nevada 10.68
23. Nebraska 11.00
24. Georgia 11.09
25. Idaho 11.28
26. Maine 11.55
27. Iowa 11.55
28. Missouri 12.06
29. North Carolina 12.31
30. Alaska 12.31
31. Delaware 12.41
32. Hawaii 12.54
33. Florida 12.67
34. Kansas 13.25
35. Pennsylvania 13.25
36. Wyoming 13.27
37. Alabama 13.32
38. Arizona 13.72
39. Tennessee 14.25
40. New Mexico 14.28
41. Texas 14.29
42. South Dakota 14.59
43. Oklahoma 14.79
44. Mississippi 15.05
45. Louisiana 15.40
46. Kentucky 15.76
47. Arkansas 16.47
48. North Dakota 16.86
49. Montana 17.25
50. South Carolina 17.60
51. West Virginia 17.63

Fatality rates per 100,000 population in individual states

1. Washington D.C. 2.37
2. Massachusetts 5.25
3. New York 5.97
4. Rhode Island 6.09
5. Washington 6.44
6. Connecticut 6.57
7. New Jersey 6.64
8. Minnesota 7.34
9. Illinois 7.43
10. California 7.51
11. Utah 7.60
12. Alaska 8.07
13. New Hampshire 8.18
14. Maryland 8.58
15. Oregon 8.62
16. Hawaii 9.05
17. Colorado 9.10
18. Nevada 9.35
19. Virginia 9.49
20. Michigan 9.49
21. Ohio 9.73
22. Pennsylvania 10.26
23. Wisconsin 10.74
24. Nebraska 11.43
25. Idaho 11.53
26. Iowa 11.87
27. Indiana 11.92
28. Georgia 12.02
29. Vermont 12.30
30. Maine 12.34
31. Delaware 12.43
32. Florida 12.55
33. Arizona 12.59
34. Texas 13.04
35. North Carolina 13.25
36. Missouri 13.72
37. Kansas 14.03
38. Louisiana 15.69
39. Tennessee 15.71
40. South Dakota 15.96
41. Kentucky 17.03
42. New Mexico 17.50
43. Alabama 17.94
44. South Carolina 18.27
45. West Virginia 18.27
46. Oklahoma 18.56
47. Arkansas 18.72
48. Mississippi 19.50
49. Montana 20.40
50. Wyoming 21.34
51. North Dakota 24.30