I did some digging in a textbook that I have on traffic and transport safety. It takes a whole bunch of statistics from the OECT/ITF yearly IRTAD Road Safety Annual Report. It's 568 pages (because it has a chapter detailing each OECD country), but the juicy bits are in the first chapter.

Looking at the longer-term developments since 2010, the number of road deaths has decreased in all countries with validated data except in the United States, Chile and Sweden. In the United States, fatalities increased by 6.3% between 2010 and 2015 and indications suggest that the situation has not improved in 2016.

The real data I think you're looking for is all in Table 1.3, Road Fatalities per 100k inhabitants, 100 billion vehicle-km and 10k registered vehicles:

If you compare the US with deaths per billion vehicle-kilometers, you can still see the US declining less fast:

          1990    2015
    FR    25.9    5.9
    SL    65.1    6.7
    UK    12.8    3.4
    US    12.9    7.0

Sidenote: it puts seatbelt use for U.S. front seat passengers at 91% (similar to other countries) and rear seats at 70% (on the low end), see page 30.