# Why 15 mph and not 10 mph or 20 mph in school zones USA **URL:** \ **Category:** Factual Questions\ **Created:** [September 1, 2009, 1:14pm UTC](https://boards.straightdope.com/t/why-15-mph-and-not-10-mph-or-20-mph-in-school-zones-usa/508475 "2009-09-01T13:14:58Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Harmonious\_Discord](https://avatars.discourse-cdn.com/v4/letter/h/74df32/32.png) [@Harmonious\_Discord](https://boards.straightdope.com/u/Harmonious_Discord)\ **Post date:** [September 1, 2009, 1:14pm UTC](https://boards.straightdope.com/t/why-15-mph-and-not-10-mph-or-20-mph-in-school-zones-usa/508475/1 "2009-09-01T13:14:58Z")
So where did the 15 mph speed for school zones come from. Was a poll taken, a random speed just brought up, or a study on child car collisions done with a significant decrease until 15 mph and lower was reached? I’m betting on no study being done to come up with the speed. Please don’t tell me it’s a traffic law as I already know that. How come that speed was used. ---
**Author:** ![Giles](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/giles/32/60_2.png) [@Giles](https://boards.straightdope.com/u/Giles)\ **Post date:** [September 1, 2009, 1:17pm UTC](https://boards.straightdope.com/t/why-15-mph-and-not-10-mph-or-20-mph-in-school-zones-usa/508475/2 "2009-09-01T13:17:47Z")
15 mph is certainly not universal. At least in this part of Ohio it’s 20 mph. ---
**Author:** ![Flymaster](https://avatars.discourse-cdn.com/v4/letter/f/c4cdca/32.png) [@Flymaster](https://boards.straightdope.com/u/Flymaster)\ **Post date:** [September 1, 2009, 1:20pm UTC](https://boards.straightdope.com/t/why-15-mph-and-not-10-mph-or-20-mph-in-school-zones-usa/508475/3 "2009-09-01T13:20:33Z")
I don’t know that I’ve ever seen a 15mph school zone. 20 seems much more common. ---
**Author:** ![panache45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/panache45/32/64_2.png) [@panache45](https://boards.straightdope.com/u/panache45)\ **Post date:** [September 1, 2009, 1:28pm UTC](https://boards.straightdope.com/t/why-15-mph-and-not-10-mph-or-20-mph-in-school-zones-usa/508475/4 "2009-09-01T13:28:03Z")
It’s 20 here. ---
**Author:** ![Snnipe\_70E](https://avatars.discourse-cdn.com/v4/letter/s/b5a626/32.png) [@Snnipe\_70E](https://boards.straightdope.com/u/Snnipe_70E)\ **Post date:** [September 1, 2009, 2:13pm UTC](https://boards.straightdope.com/t/why-15-mph-and-not-10-mph-or-20-mph-in-school-zones-usa/508475/5 "2009-09-01T14:13:02Z")
Calif it is 25 MPH ---
**Author:** ![h.sapiens](https://avatars.discourse-cdn.com/v4/letter/h/e0b2c6/32.png) [@h.sapiens](https://boards.straightdope.com/u/h.sapiens)\ **Post date:** [September 1, 2009, 2:21pm UTC](https://boards.straightdope.com/t/why-15-mph-and-not-10-mph-or-20-mph-in-school-zones-usa/508475/6 "2009-09-01T14:21:11Z")
Chicago metropolitan area is also 20, as far as I’ve ever seen. ---
**Author:** ![Susie\_Derkins](https://avatars.discourse-cdn.com/v4/letter/s/e47774/32.png) [@Susie\_Derkins](https://boards.straightdope.com/u/Susie_Derkins)\ **Post date:** [September 1, 2009, 2:23pm UTC](https://boards.straightdope.com/t/why-15-mph-and-not-10-mph-or-20-mph-in-school-zones-usa/508475/7 "2009-09-01T14:23:57Z")
20 here in Panama City, Fl. ---
**Author:** ![Kimmy\_Gibbler](https://avatars.discourse-cdn.com/v4/letter/k/bbe5ce/32.png) [@Kimmy\_Gibbler](https://boards.straightdope.com/u/Kimmy_Gibbler)\ **Post date:** [September 1, 2009, 2:32pm UTC](https://boards.straightdope.com/t/why-15-mph-and-not-10-mph-or-20-mph-in-school-zones-usa/508475/8 "2009-09-01T14:32:38Z")
You have to pick something, right? Obviously we want people to drive slowly in school zones, but just as obviously we have to balance safety with the costs of taking those precautions. Oh, I suppose you could do an elaborate study to optimize the speed limit, the number that perfectly balances keeping kids from being run over with keeping commuters happy and punctual. But, as I think you have surmised, we just took a reasonably well-informed guess. ---
**Author:** ![AncientHumanoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ancienthumanoid/32/278_2.png) [@AncientHumanoid](https://boards.straightdope.com/u/AncientHumanoid)\ **Post date:** [September 1, 2009, 2:45pm UTC](https://boards.straightdope.com/t/why-15-mph-and-not-10-mph-or-20-mph-in-school-zones-usa/508475/9 "2009-09-01T14:45:09Z")
In rural east Texas, certain highways have school zones of 45 mph, down from the 55 or 65 that they are outside of school zone areas and times (my memory is my only cite). Here in the OKC, OK area, some zones are 20, some are 25, and a few in fairly remote rural-ish areas are 35 mph. In one privately owned fairly ritzy community, the sign posted is 8 mph. The basic idea seems to be to slow down and stay alert. BTW, here in the OKC, fines for school zone violations are higher than for most regular speeding. [http://www.okc.gov/courts/costs.html](http://www.okc.gov/courts/costs.html) ---
**Author:** ![Drygon](https://avatars.discourse-cdn.com/v4/letter/d/edb3f5/32.png) [@Drygon](https://boards.straightdope.com/u/Drygon)\ **Post date:** [September 1, 2009, 3:05pm UTC](https://boards.straightdope.com/t/why-15-mph-and-not-10-mph-or-20-mph-in-school-zones-usa/508475/10 "2009-09-01T15:05:44Z")
My high school’s zone was 35. Almost everywhere else I’ve seen is 25. ---
**Author:** ![TNWPsycho](https://avatars.discourse-cdn.com/v4/letter/t/47e85d/32.png) [@TNWPsycho](https://boards.straightdope.com/u/TNWPsycho)\ **Post date:** [September 1, 2009, 3:47pm UTC](https://boards.straightdope.com/t/why-15-mph-and-not-10-mph-or-20-mph-in-school-zones-usa/508475/11 "2009-09-01T15:47:31Z")
Here in Wisconsin the speed limit a little different, we have variables. 25MPH school zone, 15 MPH when children are present. ---
**Author:** ![brad\_d](https://avatars.discourse-cdn.com/v4/letter/b/50afbb/32.png) [@brad\_d](https://boards.straightdope.com/u/brad_d)\ **Post date:** [September 1, 2009, 3:57pm UTC](https://boards.straightdope.com/t/why-15-mph-and-not-10-mph-or-20-mph-in-school-zones-usa/508475/12 "2009-09-01T15:57:03Z")
It was 20 where I grew up in Texas. I had to remember this because our house was _in_ one; when I left home I didn’t pass the sign with flashing lights to remind me the school zone speed was in effect. Back there the school zone speed limit was in effect whenever yellow lights mounted to the signs were flashing (per the wording on the signs themselves). They were timed to coincide with the starting and ending times of the school day, and _usually_ didn’t come on at midnight, on weekends or holidays, or during the summer. ---
**Author:** ![janeslogin](https://avatars.discourse-cdn.com/v4/letter/j/df788c/32.png) [@janeslogin](https://boards.straightdope.com/u/janeslogin)\ **Post date:** [September 1, 2009, 4:19pm UTC](https://boards.straightdope.com/t/why-15-mph-and-not-10-mph-or-20-mph-in-school-zones-usa/508475/13 "2009-09-01T16:19:35Z")
Most speed limits in the places I drive end in a 5. Interstates here are 75,65,55, streets are 45,35,25. I believe school zones are usually 15. One roundabout I frequent is posted at 5. Few observes that speed limit. ---
**Author:** ![AncientHumanoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ancienthumanoid/32/278_2.png) [@AncientHumanoid](https://boards.straightdope.com/u/AncientHumanoid)\ **Post date:** [September 1, 2009, 4:21pm UTC](https://boards.straightdope.com/t/why-15-mph-and-not-10-mph-or-20-mph-in-school-zones-usa/508475/14 "2009-09-01T16:21:38Z")
One of the smaller local districts here has flashing yellow lights in the street itself, along the painted lines, in addition to the sign. Pretty neat, I thought. ---
**Author:** ![DSYoungEsq](https://avatars.discourse-cdn.com/v4/letter/d/c6cbf5/32.png) [@DSYoungEsq](https://boards.straightdope.com/u/DSYoungEsq)\ **Post date:** [September 1, 2009, 4:55pm UTC](https://boards.straightdope.com/t/why-15-mph-and-not-10-mph-or-20-mph-in-school-zones-usa/508475/15 "2009-09-01T16:55:26Z")
> [@Harmonious\_Discord](#): > > So where did the 15 mph speed for school zones come from. Was a poll taken, a random speed just brought up, or a study on child car collisions done with a significant decrease until 15 mph and lower was reached? I’m betting on no study being done to come up with the speed. Please don’t tell me it’s a traffic law as I already know that. How come that speed was used. False assumption. It is not the case that school zones are uniformly 15 mph. Outside our schools here in Indian Land, which lie just off a major US highway, the school zone speed limit is 35 mph during those hours the lights blink. Regular speed limit there is 45, though many travel closer to 55, which is what they can do .5 mi. north and south of that spot. Since the limit is not universal, you can suspect what the answer to the rest of your question will be. ---
**Author:** ![SmackFu](https://avatars.discourse-cdn.com/v4/letter/s/53a042/32.png) [@SmackFu](https://boards.straightdope.com/u/SmackFu)\ **Post date:** [September 1, 2009, 5:12pm UTC](https://boards.straightdope.com/t/why-15-mph-and-not-10-mph-or-20-mph-in-school-zones-usa/508475/16 "2009-09-01T17:12:56Z")
In New York, the rule is: > [@](#): > > The numerical value of a school speed limit should be approximately ten miles per hour below the normally prevailing 85th percentile speed on the highway; or approximate the 85th percentile speed within the zone during school crossing periods. The Vehicle and Traffic Law prohibits school speed limits less than 15 miles per hour. Also, in general, this is the kind of stuff that traffic engineers love to figure out. The idea that they pull a number out of a hat is a bit silly. ---
**Author:** ![Musicat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/musicat/32/20189_2.png) [@Musicat](https://boards.straightdope.com/u/Musicat)\ **Post date:** [September 1, 2009, 5:21pm UTC](https://boards.straightdope.com/t/why-15-mph-and-not-10-mph-or-20-mph-in-school-zones-usa/508475/17 "2009-09-01T17:21:38Z")
> [@SmackFu](#): > > Also, in general, this is the kind of stuff that traffic engineers love to figure out. The idea that they pull a number out of a hat is a bit silly. But the fact that they vary so much suggests that their numbers aren’t all that well thought out, either. ---
**Author:** ![troub](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/troub/32/14802_2.png) [@troub](https://boards.straightdope.com/u/troub)\ **Post date:** [September 1, 2009, 6:05pm UTC](https://boards.straightdope.com/t/why-15-mph-and-not-10-mph-or-20-mph-in-school-zones-usa/508475/18 "2009-09-01T18:05:11Z")
> [@Musicat](#): > > But the fact that they vary so much suggests that their numbers aren’t all that well thought out, either. Not necessarily. I would just as likely assume that the limit is based on the extremely localized factors of number of lanes, visibility, curves, distance of the school/playground from the road, speed limit on the rest of the road, grade level of the school building, etc. Because these factors exist and vary widely from location to location (literally school to school, not just municipality to municipality), we can’t assume that the observed variation exists because the appropriate limit isn’t “well-thought out.” ---
**Author:** ![elmwood](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/elmwood/32/3060_2.png) [@elmwood](https://boards.straightdope.com/u/elmwood)\ **Post date:** [September 1, 2009, 6:10pm UTC](https://boards.straightdope.com/t/why-15-mph-and-not-10-mph-or-20-mph-in-school-zones-usa/508475/19 "2009-09-01T18:10:24Z")
The answers are the typical “the exception is the norm” responses one might expect. Anyhow, New Mexico is somewhat well-known for a statewide and VERY strictly enforced 15 MPH school zone speed limit. Drive 17 or 18 through an active school zone in Las Cruces, Albuquerque or anywhere else in the state, and odds are very good you’ll end up with an expensive ticket. ---
**Author:** ![Mister\_Rik](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mister_rik/32/491_2.png) [@Mister\_Rik](https://boards.straightdope.com/u/Mister_Rik)\ **Post date:** [September 1, 2009, 6:53pm UTC](https://boards.straightdope.com/t/why-15-mph-and-not-10-mph-or-20-mph-in-school-zones-usa/508475/20 "2009-09-01T18:53:06Z")
20 MPH throughout Washington state. [Next page](https://boards.straightdope.com/t/why-15-mph-and-not-10-mph-or-20-mph-in-school-zones-usa/508475.md?page=2)