180
xkcd #3248: 182.8 Meters
(imgs.xkcd.com)
Title text:
They rounded down to 182.8 instead of rounding up to 182.9 because 182.9 might make the statement incorrect.
Transcript:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3248/
I think they sometimes do that just to get people’s attention. You don’t normally see fractional speed limits so you pay more attention.
But you see 5 mph signs all over. It's in a parking lot, so it's still redundant.