WHILE WAITING IN TRAFFIC ON A COUNTY ROAD TO TURN LEFT, OUR SIENNA WAS HIT FROM BEHIND BY A CAR TRAVELING AT APPROXIMATELY 40 MPH. FRONT ROW SEATBELTS DID NOT ENGAGE, NOR DID FRONT AIRBAGS DEPLOY. OUR SIENNA HIT THE STOPPED VEHICLE IN FRONT OF US UPON IMPACT AS WELL. ONLY RIGHT SIDE CURTAIN AIRBAGS DEPLOYED AND MIDDLE ROW SEATBELTS RESTRAIN. THIS RESULTED IN MULTIPLE INJURIES TO THE FRONT ROW PASSENGERS, INCLUDING A SEVERE CONCUSSION.