debodun
SF VIP
- Location
- way upstate in New York, USA
That didn't end in a 0 or 5?
Have you ever seen a speed limit sign....
- Thread starter debodun
- Start date
Flarbalard
Senior Member
Yes, I have. It was in a factory referring to the speed limit on forklifts, 3MPH.
Ronni
Well-known Member
- Location
- Nashville TN
Nope. And you won’t ever see one at least not on public roads. Here’s why.
Speed limit signs usually end in 0 or 5 for a mix of human psychology, safety, and practicality rather than because other numbers wouldn’t work.
Here’s why
1. Easier for drivers to remember and follow
Rounded numbers are processed faster by the brain. When you’re driving, you don’t want to be doing math or double-checking whether the limit is 37 or 42. 30, 35, 40, 45 are instantly recognizable.
2. Consistency and standardization
Traffic engineers aim for consistency across roads and states. Using multiples of 5 keeps speed limits predictable and uniform, which reduces confusion—especially for out-of-state drivers.
3. Enforcement practicality. Police and courts need clear, defensible limits.
If a limit were 43 mph, enforcement arguments become messier (“I thought it was 45”). Rounded limits reduce disputes and simplify ticketing thresholds.
4. Engineering studies still round the result
Speed limits are often based on traffic engineering data (like the 85th percentile speed—the speed most drivers naturally choose).
Those calculations might produce numbers like 47 or 52 mph, but they’re almost always rounded to the nearest 5 mph for posting.
5. International convention
Many countries do the same thing (or use clean metric increments like 30, 40, 50 km/h). It’s a globally accepted approach to road safety signage.
Bottom line
Speed limits end in 0 or 5 because they are:
Speed limit signs usually end in 0 or 5 for a mix of human psychology, safety, and practicality rather than because other numbers wouldn’t work.
Here’s why
1. Easier for drivers to remember and follow
Rounded numbers are processed faster by the brain. When you’re driving, you don’t want to be doing math or double-checking whether the limit is 37 or 42. 30, 35, 40, 45 are instantly recognizable.
2. Consistency and standardization
Traffic engineers aim for consistency across roads and states. Using multiples of 5 keeps speed limits predictable and uniform, which reduces confusion—especially for out-of-state drivers.
3. Enforcement practicality. Police and courts need clear, defensible limits.
If a limit were 43 mph, enforcement arguments become messier (“I thought it was 45”). Rounded limits reduce disputes and simplify ticketing thresholds.
4. Engineering studies still round the result
Speed limits are often based on traffic engineering data (like the 85th percentile speed—the speed most drivers naturally choose).
Those calculations might produce numbers like 47 or 52 mph, but they’re almost always rounded to the nearest 5 mph for posting.
5. International convention
Many countries do the same thing (or use clean metric increments like 30, 40, 50 km/h). It’s a globally accepted approach to road safety signage.
Bottom line
Speed limits end in 0 or 5 because they are:
- Faster to read
- Easier to remember
- Simpler to enforce
- Safer and more consistent
