NPR's Robert Siegel and Michael Minielly, a Mercedes-Benz representative, drive a new S550 4Matic, which allows for semi-autonomous driving. Rob Ballenger /NPR hide caption

itoggle caption Rob Ballenger /NPR

Central African Republic's interim President Michel Djotodia sits during a conference in Bangui in this Dec. 8 file photo. Djotodia resigned Friday after a two-day summit in neighboring Chad. Herve Serefio/Reuters/Landov hide caption

itoggle caption Herve Serefio/Reuters/Landov