Both the NHTSA and the IIHS have crash-tested the 2010 Audi A4. Both agencies give the 2010 Audi A4 the highest safety ratings possible.
Popular Mechanics lists the A4's safety options, which include "active cruise control, lane monitoring and collision warning-not to mention Audi side assist, a radar-based system that warns against vehicles approaching from the rear three-quarter view-often a potential blind spot for drivers." There's also a backup camera, Cars.com reports.
TheCarConnection.com points out that the Audi A4's rear seat also has headrests for all three passengers. Visibility in both the wagon and sedan is quite good, even with those headrests in the upright position.