As others have stated, it was not just the BMW halogen headlights that rated poor or marginal in the IIHS test. The IIHS article presents test data for several lighting options offered by BMW in the cars tested.
In the 3 series the LED headlights with automatic switching to high beams were rated marginal. The LED headlights without automatic switching and the halogen headlights were both rated poor.
http://www.iihs.org/iihs/ratings/veh...s-4-door-sedan
In the 2 series the HID (Xenon) headlights with automatic switching to high beams were rated marginal. The HID headlights without automatic switching and the halogen headlights (with and without automatic switching) were both rated poor.
http://www.iihs.org/iihs/ratings/veh...s-2-door-coupe
Looking at the detailed information, the performance of the HID headlights with and without automatic switching appears the same in the IIHS tests. Presumably a driver could activate high beams when it is safe to do so as efficiently as the automatic system. However, the IIHS article states for HID headlamps with automatic switching: "High-beam assist compensates for some limitations of this vehicle's low beams on the straightaway and on both left curves." This apparently justifies the higher "marginal" rating for the HID headlamps when equipped with automatic switching. This methodology appears questionable.
On the other hand, the performance of the LED headlights in the 3 series appears different with and without automatic switching in the IIHS tests. The LED low beams appear to provide the required light level at greater distances when the automatic switching is present. The article states for the LED headlights with automatic switching: "High-beam assist compensates for some limitations of this vehicle's low beams on the straightaway and all 4 curves."