The 2007 LS class is the flagship vehicle from Lexus, however the 2007 Lexus LS460 does rather poorly in the Rear Crash Test, it only scores a "Marginal".
The LS460 was outrated in the rear crash Test by the Audi A6, Mercedes E Class and the BMW 5 Series.
Ratings -
1.Good
2.Acceptable
3.Marginal
4.Poor
IIHS Crash Test Large Luxury cars
2007 Lexus LS 460 - Front - Good, Side - Not tested, Rear MARGINAL
2007 Audi A6 - Front- Good, Side - Good, Rear - Good
2007 Mercedes E Class - Front Good, Side - Acceptable, Rear Good
2007 BMW 5 series - Front Good, Side - not tested, Rear - Good
The Mercedes S Class, Audi A8 and BMW 7 Series have not been tested as yet.
The above results are listed at - http://www.iihs.org/ratings/summary.aspx?class=10