When exiting a highway, when should you begin to slow down?

When exiting a highway, the appropriate time to begin slowing down is when you are in the exit lane. This is important because the exit lane typically allows for a gradual reduction in speed, which is safer and helps maintain traffic flow. Entering the exit lane at highway speeds and then abruptly slowing down can create hazards for both the exiting vehicle and other road users.

As you approach the exit, maintaining proper speed until you are securely in the exit lane helps prevent unexpected movements that could lead to collisions. Additionally, once in the exit lane, it's important to check mirrors and blind spots while reducing your speed appropriately, preparing to navigate the turn safely.

Other points in the question relate to the timing of signaling and awareness of exit signage, which are important aspects of driving but do not indicate the optimal moment to begin slowing down relative to highway exits.