ENGINE[XXX] Wednesday we were traveling from Charlotte NC headed westbound on [XXX], a 6 or 8 lane highway, speed limit 70+ mph, when our 2021 Lincoln Navigator suddenly lurched and the engine completely failed. There weren't any warnings by the vehicle prior to the incident. There were two of us in the vehicle at the time, and we suddenly found ourselves in a situation of extreme risk. It was 4 - 5 pm during rush hour traffic. The driver was able to maintain composure and our tires continued rotating long enough to coast and cross over 3 fast moving lanes to get us slightly off the side of the highway. It was a very frightening and unsafe situation, not only during but after the engine failure, as we were on a very busy, noisy highway not knowing where we were or what to do. We live in Ohio and our plans were scheduled only for 8/25/24 (leave Ohio)-8/29/24 (return to Ohio). Our Lincoln was towed the night of the engine failure to Classic Ford Lincoln in Shelby NC, and it's been there for 7 days. The tow driver could not start the engine. He had difficulty (20 minutes trying) getting it into neutral so he could put it on the flatbed. The total engine failure problem isn't yet diagnosed. Classic is the only one to examine it. We had to extend our NC hotel stay for two days waiting for the vehicle to be repaired. On 8/31 we couldn't wait any longer and had to rent a vehicle from Enterprise to return home; leaving our Navigator in NC. Lincoln Roadside Assistance has been very difficult and inattentive to our dire circumstances. We're now faced with a situation of not having our vehicle, not having a diagnosis, and concerns about whether the vehicle will be dependable when/if it's returned to us. We have to travel often and fear Lincoln could leave us in bad circumstances again even if they can find the current problem and repair it. It seems to be something extraordinary or uncommon or a diagnosis would have happened by now. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOIA), 5 U.S.C. 552(B)(6)