OUR CAR IMPACTED WITH ANOTHER AS WE TRIED TO ENTER THE HIGHWAY FROM A SHORT MERGE LANE. THE OTHER CAR ENTERED IN FRONT OF US FROM THE SIDE OF THE ROAD AFTER WE PASSED A STOP SIGN IN THE MERGE LANE; THE OTHER CAR THEN STOPPED SHORT BEFORE ENTERING THE HIGHWAY, JUST AS WE WERE SPEEDING UP THE ENTER THE HIGHWAY. A SENSOR SOUNDED IN OUR CAR, WE SLAMMED ON THE BRAKES, AND THE TWO CARES COLLIDED. THE PASSENGER SIDE FRONT OF OUR VEHICLE WAS DAMAGED; THE REAR DRIVE SIDE OF THE OTHER CAR WAS DAMAGED. DRIVER SIDE SEATBELT IN OUR CAR OPERATED NORMALLY. PASSENGER SIDE SEATBELT IN OUR CAR LOOSENED INSTEAD OF TIGHTENED; PASSENGER HIT HEAD ON DASHBOARD AS BRAKES WERE HIT OR IMPACT HAPPENED (WE WERE GOING APPROX. 15 MPH. UPON IMPACT). SAID PASSENGER OBSERVED UPON IMPACT OF HEAD ON DASH THAT HER SEAT BELT WAS HANGING SLACK AWAY FROM HER CHEST BY APPROX. SIX TO EIGHT INCHES. TOYOTA PRODUCT LIABILITY DEPT. WAS INFORMED (CASE NUMBER 210409002008) BETWEEN 6:15 AND 7:30 PM ON FRIDAY, APRIL 9TH, 2021. THEY SAY THEY WILL DOWNLOAD THE "BLACK BOX" INFORMATION, BUT THEY HAVEN'T COMMITTED TO A PHYSICAL INSPECTION OF THE SEATBELT, WHICH SEEMS CRITICAL (I.E., THAT A SEATBELT ENGINEER PHYSICALLY INVESTIGATE).*DT