Lawful brakes must be able to stop a car traveling at 20 miles per hour within 20 feet , not including thinking distance.

Quick Scoop: The Core Answer

When a question says “not including thinking distance” , it’s only asking about the braking distance – the distance the car travels after the brakes are applied.

According to guidance referenced in driver-ed style materials and explanations that cite National Highway Traffic Safety Administration standards, lawful brakes at 20 mph should stop a car within 20 feet of actual braking distance.

Why 20 Feet (And Not More)?

Some older Q&A and forum-style sites mention numbers like 25–30 feet or even higher, but those usually mix together:

  • thinking distance (reaction time)
  • plus braking distance
  • plus allowances for road and vehicle conditions.

Your question explicitly excludes thinking distance , which is why the correct figure is the shorter one: 20 feet of braking distance at 20 mph.

So if this is a multiple‑choice test question and the options include 10, 20, 30, 40 feet, the expected correct answer is: 20 feet.

Mini Story: How This Plays Out

Imagine you’re driving at 20 mph on a clear, dry road.
The moment you see a hazard and slam the brakes, the car still needs a short distance to physically come to a stop. Under lawful, properly functioning brakes , that pure braking segment should be about 20 feet from the instant you press the pedal to the full stop, assuming good conditions and no reaction delay.

TL;DR

  • Question asks for braking distance only , not including thinking distance.
  • At 20 mph , lawful brakes must stop a car within 20 feet of braking distance. ✅

Information gathered from public forums or data available on the internet and portrayed here.