You are driving at night on an unlit rural road with your high-beam headlights on. As you … — DMV Permit Practice Test

You are driving at night on an unlit rural road with your high-beam headlights on. As you round a curve at $48\text{ mph}$ , you observe an oncoming vehicle approximately $450\text{ feet}$ away. At the same time, you realize that if you switch to low-beam headlights, their illumination distance of $150\text{ feet}$ will be shorter than your vehicle's total stopping distance of $185\text{ feet}$ at your current speed. Which combination of actions is legally required and safest under these conditions?

Immediately dim your high beams to low beams because the oncoming vehicle is within 500 feet, and reduce your speed so your total stopping distance remains within your 150-foot low-beam headlight range.Answer
B
Maintain your high beams until the oncoming vehicle gets within 300 feet, while maintaining 48 mph because you are driving within the posted speed limit.
C
Dim your high beams to low beams immediately, but maintain your speed at 48 mph since driving below the posted speed limit is always considered safe at night.
D
Switch to parking lights to prevent glaring the oncoming driver while maintaining your current speed until the vehicle passes.

Answer

Immediately dim your high beams to low beams because the oncoming vehicle is within 500 feet, and reduce your speed so your total stopping distance remains within your 150-foot low-beam headlight range.

Traffic laws mandate dimming high-beam headlights within 500 feet of an oncoming vehicle to prevent blinding the driver. Furthermore, when operating on low beams with an illumination range of 150 feet, continuing to drive at a speed requiring an 185-foot stopping distance violates the Basic Speed Law (overdriving headlights). The driver must dim the headlights immediately and reduce speed so the vehicle can stop safely within the illuminated distance.

Step-by-Step Solution

Determine the legal requirement for high-beam dimming when approaching oncoming traffic.

High beams must be dimmed to low beams within

500\text{ feet}

of an oncoming vehicle. Since the vehicle is

450\text{ feet}

away, high beams must be dimmed immediately.

Prevents blinding oncoming drivers with headlight glare.

Evaluate stopping distance against low-beam visibility range.

The low-beam visibility range is

150\text{ feet}

, but total stopping distance at

48\text{ mph}

185\text{ feet}

Driving at a speed where stopping distance exceeds headlight illumination range is known as overdriving headlights.

Apply the Basic Speed Law to determine necessary speed adjustment.

Reduce speed so that the vehicle can come to a complete stop within the

150\text{ feet}

visible range of the low-beam headlights.

The Basic Speed Law dictates driving at a safe speed for existing conditions, regardless of posted limits.

Key Concept

High-beam dimming distance rules and avoiding overdriving headlights under the Basic Speed Law

Estimated Time:1m 30s

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