Calculating the 85th Percentile Speed

Jonah Finkelstein provides a summary of the uses of the 85th percentile speeds, why it is important, and how to calculate the 85th percentile speed on a roadway using collected speed data.

[@mackdrzayich7037]

Should the speed limit be higher, or should the design speed be lowered? Can't believe we're still using 85th percentile to set speed limits.

[@gregorteply9034]

Or should you shut up?

[@aimxdy8680]

higher, we haven’t done free flowing traffic speed since the late 1980s lol, in the late 1980s the average passenger car sped was around 75-80 mph and the average truck speed was like 60-65.

[@MR-il3ez]

awesome explanation!

[@Uros141]

So how do you calcualate what is the exact 85th percentile speed? Is it 621, 62.3 or 62.8 mph?