---
title: "Driver reaction to a surprise: 1.35 s"
description: "Driver reaction to a surprise: typically 1.35 s, really 1.10 s to 1.80 s. What is measured, and why it counts as a reaction."
url: https://atoneplace.net/reaction-time/driver-reaction-surprise/
site: "At One Place"
---

# Driver reaction to a surprise

**Driver reaction to a surprise: 1.10 s–1.80 s**

Reaction — a decision, via the brain

A genuine surprise costs roughly half a second on top of an expected event, and the spread widens sharply because some drivers do not recognise the hazard at all for a while. This is the figure that matters for real crashes, and it is why following distance is expressed in seconds rather than car lengths. At 100 km/h a 1.35-second reaction is 37 metres before any braking begins.

## The numbers

- **Typical:** 1.35 s
- **Range:** 1.10 s to 1.80 s
- **What it is:** Reaction — a decision, via the brain
- **What is measured:** Unanticipated hazard — a car pulling out, an obstacle appearing; time to the brake pedal.

## Why this is a reaction

A reaction is a decision: signal in, processing, movement out. The floor for a human is around 150 milliseconds, and anything measured below about 100 ms is anticipation rather than response.

## Where it sits against everything else

*Reflexes at the top, reactions in the middle, design values off the end of the scale.*

- Vestibulo-ocular reflex — Reflex: 10 ms
- Knee-jerk (patellar) reflex — Reflex: 22 ms
- Latency added by your screen and mouse — Physical limit: 35 ms
- Blink reflex — Reflex: 40 ms
- Withdrawal reflex — Reflex: 90 ms
- Time a jab takes to land — Physical limit: 110 ms
- Sprint start reaction — Reaction: 140 ms
- Simple tactile reaction time — Reaction: 155 ms
- Simple auditory reaction time — Reaction: 170 ms
- Professional gamer reaction time — Reaction: 190 ms
- Formula One start reaction — Reaction: 200 ms
- Simple visual reaction time — Reaction: 250 ms
- How reaction time changes with age — Reaction: 250 ms
- What sleep loss does to reaction time — Reaction: 300 ms
- What alcohol does to reaction time — Reaction: 320 ms
- Recognition reaction time — Reaction: 340 ms
- Choice reaction time — Reaction: 380 ms
- Time to hit a 95 mph fastball — Physical limit: 400 ms
- Time a goalkeeper has on a penalty — Physical limit: 450 ms
- Time to play a 90 mph delivery — Physical limit: 500 ms
- Driver reaction to an expected event — Reaction: 850 ms
- Driver reaction to a surprise — Reaction: 1.35 s

## Driving

| What | Typical | Range | Kind |
| --- | --- | --- | --- |
| Driver reaction to an expected event | 850 ms | 700 ms–1 s | Reaction |
| The 2.5-second road design figure | 2.50 s | 2.50 s–2.50 s | Design value |

## Common questions

### How long is driver reaction to a surprise?

Typically 1.35 s, with a real range of 1.10 s to 1.80 s. Unanticipated hazard — a car pulling out, an obstacle appearing; time to the brake pedal.

### Is that a reflex or a reaction?

Reaction — a decision, via the brain. A reaction is a decision: signal in, processing, movement out. The floor for a human is around 150 milliseconds, and anything measured below about 100 ms is anticipation rather than response.

## Related pages

- [Driver reaction to an expected event](https://atoneplace.net/reaction-time/driver-reaction-expected/)
- [The 2.5-second road design figure](https://atoneplace.net/reaction-time/aashto-perception-reaction/)
- [A reflex is not a reaction](https://atoneplace.net/reaction-time/reflex-vs-reaction/)
- [Stopping distance at every speed](https://atoneplace.net/reaction-time/stopping-distance/)
- [Measure your own reaction time](https://atoneplace.net/tools/reaction-time-test/)

## Sources

- Typical range compiled from manufacturer specifications — At One Place (/about/)