Final answer:
The advancement in vehicle design is the high-mounted stop light, commonly known as the center high mount stop lamp (CHMSL), which provides an additional visual indication for drivers that the vehicle ahead is stopping or preparing to stop.
Step-by-step explanation:
An advancement in vehicle design that gives following drivers an added warning that the vehicle ahead intends to stop or turn is the high-mounted stop light. This additional safety feature, known as a center high mount stop lamp (CHMSL), enhances the visibility of the vehicle's braking action. It's positioned at eye level or higher, often on the rear windshield or just above the rear deck of the vehicle, thereby improving the probability that following drivers will notice the vehicle slowing down or preparing to stop, particularly in heavy traffic conditions where visibility might otherwise be obstructed.