Let's say a vehicle enters an inactive school zone going exactly the speed limit of 30mph. Then the school zone (20mph) turns on while the vehicle is still inside.

What is the current speed limit for that driver?

If it is 20mph, is there any allowance for drivers to adjust their speed or are they instantly breaking the law?

My interpretation has been that the speed limit remains 30mph in this case for the vehicles that entered an inactive school zone.


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    Do you mean if you enter a school zone at 6:59:55 and 5 seconds later, while you are still in the zone, the limit changes? Is there an electronic sign that changes, or is there a fixed sign like "School zone, Speed limit 20 MPH 7 am- 4pm weekdays"? – Damila Oct 16 '19 at 14:10
  • Yes to your first question. The sign says "School, speed limit 20 when flashing" with a flashing light at the beginning and end of the zone. I can add a picture in original question if it helps. I'm in this situation regularly in my morning commute. The specific school zone is quite long and police presence there is common. – 5AM Oct 16 '19 at 14:30
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    Interesting, so "when flashing" but no posted time? Sorry, I don't have an answer for you but I agree it seems unfair to start the flashing after you enter (and then charge you). If it was a posted time, I would think the driver is responsible for knowing the time. – Damila Oct 16 '19 at 14:34
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    Seems like gradually and safely reducing to the new speed would be the wisest course of action. – Justin Oct 16 '19 at 15:40
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    I've had similar thoughts as I drive through a school zone that has the same signage that you posted. I haven't tried this defense yet, but I always visualize the sign (and the line in the road indicating the beginning of the zone) as a magic wand. Every time a car passes the line, the wand taps the car and says 'I set your max legal speed to X' where X is either the reduced speed (if flashing) or the normal speed. In that sense, the restriction would be placed on the vehicle (cannot go faster than X) rather than the road itself (cannot be traveled on at speeds over X). Great question! – Brian R Oct 17 '19 at 16:51

At least in NC, the law is unclear on the issue. However, it is my (and thanks to Brian R's comment, not everyone's) experience that such signs, flashing or with posted times, are posted every few feet within the zone.

Thus, even if the first sign you pass was not flashing, if subsequent ones begin flashing, you should reduce speed.

It may be a good idea to invest in a cheap dashcam which you have on in your morning commute. This way, in the event you are pulled over after passing a school zone sign which is not flashing, you have evidence to show the judge.

Also check the laws on the state where you live to see if there are any applicable statutes.

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    "However, it is my experience that such signs, flashing or with posted times, are posted every few feet within the zone." In Texas, I have never seen this. There is often one sign at the beginning of the zone and one sign at the end (sometimes just a line on the road at the end). Rarely there will be some kind of overhead sign 0.5-1 miles in advance of the beginning of the zone to warn of the upcoming change (if the reduction in speed is drastic). – Brian R Oct 17 '19 at 16:53

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