According to reviews read by TheCarConnection.com, the BMW 5-Series has crash-test scores that simply aren’t competitive with those of top-drawer luxury sedans. The 2009 M5 hasn't been tested by either of the crash-test authorities, but the virtually identical 5-Series on which it's based has, and you can expect similar results.
The Insurance Institute for Highway Safety (IIHS) awarded the 5-Series the highest possible rating, "good," for the IIHS's frontal offset impact test. But without the optional side-impact airbags installed, the BMW 5-Series only earned a "marginal" score, the second-worst score possible, in the IIHS side-impact test. In National Highway Traffic Safety Administration (NHTSA) tests, the 5-Series scored quite well, with one notable exception. NHTSA awarded the BMW 5er a perfect five-star rating for side impact tests, as well as a five-star rating for passenger-side front impacts. Unfortunately, the 2009 BMW 5-Series, and accordingly the M5 BMW, earned only three out of a possible five stars for driver front-impact protection.
Regarding safety features, Cars.com reports that the BMW M5 has "side-impact airbags for the front seats, side curtain airbags and Dynamic Stability Control" as standard, as well as "traction control," according to Edmunds. Kelley Blue Book also notes the "sophisticated set of electronic stability, traction and brake controls" included on the M5 BMW. In terms of optional safety features, the BMW M5 offers two. Edmunds lists these M5 BMW safety add-ons as "rear seat side airbags and active head restraints," which move forward to help prevent whiplash in the event of a collision. Cars.com notes a "Park Distance Control" system comes standard to help with close parking maneuvers.