What is 'Tunnel Vision' (Tunnelblick) caused by excessive vehicle speed or severe stress, and how does it endanger driving safety?

1. Driving through a mountain tunnel with sunglasses on
2. The narrowing of the effective visual field as speed or cognitive stress increases, causing the driver to miss peripheral hazards such as pedestrians, cyclists, and side street traffic
3. A mechanical defect in the headlight lenses
4. The optical reflection of trees on the windshield