This is a relative matter. The autobahn, without speed limits, is safer than US high ways with speed limits. The speed limit being suggested there is also a higher speed than the speeds reached on most US highways, which were a clone of the autobahn. Research into this matter has long suggested that there is an optimal limit at the 85th percentile and setting a speed limit above or below it harms safety. The autobahn demonstrates the optimal limit is well above the limits that are used in the U.S., which coincidentally are well below the 85th percentile.
The autobahn with speed limits is demonstated to be safer than the autobahn without - there's no need to compare to US highways. You could compare the autobahn with germanies european neighbors, but the better comparison is the article that I posted in my previous comment. The same 62km long segment of autobahn, no infrastructure changes, compared with and without speed limit. The posted speed limit of 130km/h is also largely in line with US speed limits.
