Get terms from multiple taxonomies

If you want to retrieve multiple taxonomies you need to put the four taxonomies in an array, you are doing this, but you have put taxonomy=> in the array.

$terms = get_terms(
          'taxonomy' => array(
                         'vehicle_safely_features',
                         'vehicle_exterior_features',
                         'vehicle_interior_features',
                         'vehicle_extras')
);

Hope it helps