How are speed limits calculated?
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Where I live they’re supposed to be 85% of the average speed when measured. So if I measure a bunch of cars in an area and that average is 70ish, the speed limit should be 60. That doesn’t always work in practice, though. More often than not they simply assign a stretch of road with those of like characteristics (residential, straight vs. curved, etc.) and assign a speed limit the same as other similar roads.
Something interesting that I also recently learned from a traffic engineer friend, in my state they can’t lower the speed limit in a construction zone by anymore than 10mph. On a highway near me the normal speed limit is 70mph. Currently they’re doing construction that has traffic reduced to a single lane with Jersey barriers on each side. So, the construction workers have to work alongside tractor trailers doing 60 through a 10 foot wide cattle chute. Scary.
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