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.