The U.S. auto industry is racing to open seven new assembly plants, with giants like Toyota, Ford, Rivian, Lucid, Hyundai, Vin Fast, Scout, and Slate betting on an extra 1.8 million vehicles. Yet current factories run below 70% capacity, leaving roughly 4 million idle units. This expansion follows ten‑year product cycles and five‑year strategies, ignoring a looming 20‑year horizon where technology and demographics reshape demand.

Autonomous “robotaxis” are already picking up passengers, while companies such as Mercedes, Tesla, and Lucid predict consumer showrooms for robocars this decade. Shared fleets and vertical takeoff aircraft will siphon off premium buyers, and micromobility options eat short‑trip demand. Each household that drops a second or third car erodes sales forecasts.

The deeper threat is demographic. U.S. population growth has slowed, and many markets—China, Japan, South Korea, Italy, Greece, Portugal, and Eastern Europe—are already shrinking. Fewer teenagers will obtain licenses, curtailing the traditional sales cycle. If new‑car sales struggle today despite a strong economy, the outlook for 2046 is dire.

Boards must look beyond quarterly results and start planning for 2046 today, or risk a historic overcapacity disaster.