Speed limits have been raised in three US states.
In Texas, the limit went up to 80mph on rural interstates, in Iowa it rises to 70mph, again on rural roads, while in May, the limit in Indiana went from 65mph to 70mph in areas with less than 50,000 population -- one supposes you aren't supposed to count them first. Lorries go faster too -- their limit went up to 65mph.
Recent responses on one US forum included a clipping from a Montana state press release, as follows: "In 1999, after 4 years of no numerical or posted daytime speed limit on these classifications of highways, outside of urban areas, Montana recorded its lowest fatality rate. For the last 5 months of no daytime limits in Montana, the period after its Supreme Court had ruled that the Reasonable and Prudent law was unconstitutional, reported fatal accident rate declined to a record low. Fixed speed limits were reinstated on Memorial Day weekend 1999. Since then, fatal accidents have begun to rise again."