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 850 ms
- The 2.5-second road design figure 2.50 s
- A reflex is not a reaction Why one is 20 ms and the other 250
- Stopping distance at every speed Reaction distance plus braking distance, computed
- Measure your own reaction time Five attempts, median reported
Sources
- Typical range compiled from manufacturer specifications — At One Place