# When do speed limits take effect? **URL:** \ **Category:** Factual Questions\ **Created:** [March 14, 2005, 10:45pm UTC](https://boards.straightdope.com/t/when-do-speed-limits-take-effect/294533 "2005-03-14T22:45:22Z")\ **Posts on this page:** 17\ **Page:** 2
**Author:** ![Nic2004](https://avatars.discourse-cdn.com/v4/letter/n/4491bb/32.png) [@Nic2004](https://boards.straightdope.com/u/Nic2004)\ **Post date:** [March 16, 2005, 1:37pm UTC](https://boards.straightdope.com/t/when-do-speed-limits-take-effect/294533/21 "2005-03-16T13:37:08Z")
> [@Emilio Lizardo](#): > > If you’ll pardon a tangential hijack: what is the “range” of a No Parking sign? I live near a high school, so my street is designated for zoned parking only. All up and down the street, spaced every hundred feet or so, are signs saying “zoned parking only 8 AM to 6 PM.” Except for the one sign in front of MY house, which specifies **6** AM to 6 PM. Where does the 6 AM zone begin and end under those circumstances? Off hand I’d say the posting time on your sign is a mistake by the sign shop. Call the jurisdiction that posted it (City or County) and tell them of the mistake. The times should be consistent. To answer your question though, the range varies a little based on things like posted speed and sight visibility. The state statutes usually read something like " **Must be readily apparent to a normally observant driver**" and they extend between signs and either have a sign with an arrow pointing into the zone (as opposed to a two way arrow) at the end or at a natural break like an intersection. ---
**Author:** ![RTFirefly](https://avatars.discourse-cdn.com/v4/letter/r/c77e96/32.png) [@RTFirefly](https://boards.straightdope.com/u/RTFirefly)\ **Post date:** [March 16, 2005, 3:49pm UTC](https://boards.straightdope.com/t/when-do-speed-limits-take-effect/294533/22 "2005-03-16T15:49:36Z")
> [@Nicodemus2004](#): > > As a small aside FYI. It is off topic a bit but thought you might like to know that when you pull up to a traffic signal, your vehicle is detected not by weight of the car but by magnetic sensors in the pavement that work much like the treasure finders you sometimes see people using loolking for coins and such. Is there enough metal in a bicycle for the damned things to notice, and if so, any suggestions on how best to activate the sensors with a bike? > [@danceswithcats](#): > > IANALEO but… Hey, I don’t care about your Zodiac sign. Would you be more of an expert if you _were_ a Leo? 😃 ---
**Author:** ![Nic2004](https://avatars.discourse-cdn.com/v4/letter/n/4491bb/32.png) [@Nic2004](https://boards.straightdope.com/u/Nic2004)\ **Post date:** [March 16, 2005, 9:29pm UTC](https://boards.straightdope.com/t/when-do-speed-limits-take-effect/294533/23 "2005-03-16T21:29:24Z")
> [@RTFirefly](#): > > Is there enough metal in a bicycle for the damned things to notice, and if so, any suggestions on how best to activate the sensors with a bike? Yes, it is possible. However, there is a detector in the controller box (usually the aluminum box on the corner) that can be tuned for sensitivtiy. Too much, and it picks up the earth’s magnetic fluctuations and stays on; too little and it won’t pick up a truck. Problem sometimes is many new bikes, and some motorcycles for that matter, have many composites and little metal. For your best shot, next time you approach the stop bar in a turn lane, look for the tar-filled pavement cuts in the form of a long rectangle split long-axis by a third line. This is the loop sensor and the magnetic sensitivity is greatest over the center of the three lines. However, if it is out of tune, placement won’t help but calling the maintaining agency and asking to have the “_ **loop detectors be tuned to detect my bicycle** _” may help (the verbage may help get their attention) Sorry for the difficult descriptions… if I can’t draw a picture I feel my hands are tied. I hope this helps ---
**Author:** ![Spoke](https://avatars.discourse-cdn.com/v4/letter/s/a88e57/32.png) [@Spoke](https://boards.straightdope.com/u/Spoke)\ **Post date:** [March 16, 2005, 11:04pm UTC](https://boards.straightdope.com/t/when-do-speed-limits-take-effect/294533/24 "2005-03-16T23:04:32Z")
> [@gotpasswords](#): > > The speed limit takes effect at the exact point the sign is located. Go past that 25 sign at 27 mph and you’re fair game for a speeding ticket. As a practical matter, though, some states prohibit the use of radar guns within _x_ feet of a sign reducing the speed limit. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [March 16, 2005, 11:53pm UTC](https://boards.straightdope.com/t/when-do-speed-limits-take-effect/294533/25 "2005-03-16T23:53:00Z")
> [@Nicodemus2004](#): > > your vehicle is detected not by weight of the car but by magnetic sensors in the pavement… The large square or retangular cuts in the pavement ( on the approach in thru-lanes and up at the stop bar in turn-lanes) detect the metal in your car and signal the controller to give you a place in the timing cycle. True, but these are being [phased out](http://transops.tamu.edu/content/sensors.cfm) for a variety of reasons. ---
**Author:** ![Nic2004](https://avatars.discourse-cdn.com/v4/letter/n/4491bb/32.png) [@Nic2004](https://boards.straightdope.com/u/Nic2004)\ **Post date:** [March 17, 2005, 12:05am UTC](https://boards.straightdope.com/t/when-do-speed-limits-take-effect/294533/26 "2005-03-17T00:05:30Z")
> [@Crafter\_Man](#): > > True, but these are being [phased out](http://transops.tamu.edu/content/sensors.cfm) for a variety of reasons. True, and a good site. I was telling them of what commonly exists in the field… what most people will likely encounter. The overhead presence detectors and implanted cylinders and others are good upcoming tech pioneered by Texas and California but as yet uncommon in most of the the traffic areas. Also, many of the problems addressed were not experianced by our department. Perhaps the less-severe range of weather conditions in the more temperate areas? Regardless, thanks for the site. It’s good to keep up with the new stuff. ---
**Author:** ![Scarlett67](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/scarlett67/32/7387_2.png) [@Scarlett67](https://boards.straightdope.com/u/Scarlett67)\ **Post date:** [March 18, 2005, 7:28pm UTC](https://boards.straightdope.com/t/when-do-speed-limits-take-effect/294533/27 "2005-03-18T19:28:16Z")
> [@cmkeller](#): > > Are these two spots anywhere near Ripon? Because in my only trip to/through Wisconsin, that’s where I got a ticket . . . And I _was_ on my way to Appleton, though I was coming from Wisconsin Dells rather than from Madison. Yup, Rosendale is about 10 miles west of Ripon on Hwy. 23. ---
**Author:** ![gigi](https://avatars.discourse-cdn.com/v4/letter/g/a587f6/32.png) [@gigi](https://boards.straightdope.com/u/gigi)\ **Post date:** [March 18, 2005, 9:20pm UTC](https://boards.straightdope.com/t/when-do-speed-limits-take-effect/294533/28 "2005-03-18T21:20:47Z")
> [@Thalion](#): > > I’d love to see a cite for that. It doesn’t make much sense to base a speed limit on where you can “reasonable read the sign”. That would make the speed zones different for people with different eyesight. Interesting…I was told that they go into effect when you can see the sign by my driving instruction who was of course very strict about these legalities. I always wondered about it though, because of course when you know an area you know what a sign says from quite a way off even if you can’t actually read it, so would that count? ---
**Author:** ![Scarlett67](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/scarlett67/32/7387_2.png) [@Scarlett67](https://boards.straightdope.com/u/Scarlett67)\ **Post date:** [March 18, 2005, 10:39pm UTC](https://boards.straightdope.com/t/when-do-speed-limits-take-effect/294533/29 "2005-03-18T22:39:24Z")
Crap. Make that EAST of Ripon. :smack: ---
**Author:** ![Nic2004](https://avatars.discourse-cdn.com/v4/letter/n/4491bb/32.png) [@Nic2004](https://boards.straightdope.com/u/Nic2004)\ **Post date:** [March 19, 2005, 2:05am UTC](https://boards.straightdope.com/t/when-do-speed-limits-take-effect/294533/30 "2005-03-19T02:05:49Z")
> [@gigi](#): > > Interesting…I was told that they go into effect when you can see the sign by my driving instruction who was of course very strict about these legalities. I always wondered about it though, because of course when you know an area you know what a sign says from quite a way off even if you can’t actually read it, so would that count? **gigi** - I can’t speak to the Traffic Laws in the area you are in as I don’t know that info. However, I do know that all of those I have been aware of are quite specific as to the place were they take effect. One difference is the type of sign. There are Yellow and Black **Warning** signs (like a curve sign) that are placed in advance of the condition to allow time to react (slow, turn, etc.) but are not what are considered enforceable… only advisory. Then there are Red and White or White and Black **Regulatory** signs (Stop and Speed Limits respectively) that are placed were the compliance is required… and enforceable. Don’t stop were you are first able to see the Stop sign, only at the sign or the white stop bar. ---
**Author:** ![WhyNot](https://avatars.discourse-cdn.com/v4/letter/w/c77e96/32.png) [@WhyNot](https://boards.straightdope.com/u/WhyNot)\ **Post date:** [March 19, 2005, 3:18am UTC](https://boards.straightdope.com/t/when-do-speed-limits-take-effect/294533/31 "2005-03-19T03:18:49Z")
> [@Nicodemus2004](#): > > There are Yellow and Black **Warning** signs (like a curve sign) that are placed in advance of the condition to allow time to react (slow, turn, etc.) but are not what are considered enforceable… only advisory. I seem to remember that the **CURVE - 20 MPH** signs on Lake Shore Drive are yellow. Does that mean 20 is just a suggestion and we’re legally able to go whipping around the corners at 45? (Most of us natives actually do more like 50-55, but we’ll pretend we’re going the 45 speed limit that exists on the rest of the drive…) ---
**Author:** ![Thalion](https://avatars.discourse-cdn.com/v4/letter/t/f475e1/32.png) [@Thalion](https://boards.straightdope.com/u/Thalion)\ **Post date:** [March 19, 2005, 3:28am UTC](https://boards.straightdope.com/t/when-do-speed-limits-take-effect/294533/32 "2005-03-19T03:28:50Z")
> [@WhyNot](#): > > I seem to remember that the **CURVE - 20 MPH** signs on Lake Shore Drive are yellow. Does that mean 20 is just a suggestion and we’re legally able to go whipping around the corners at 45? Technically, yes. The yellow signs are only advisory, not regulatory. However, should you get in an accident while going at a speed above the advised speed, you could be cited for _Speed Too Fast for Conditions_ (at least here in Washington state). ---
**Author:** ![Nic2004](https://avatars.discourse-cdn.com/v4/letter/n/4491bb/32.png) [@Nic2004](https://boards.straightdope.com/u/Nic2004)\ **Post date:** [March 19, 2005, 3:32am UTC](https://boards.straightdope.com/t/when-do-speed-limits-take-effect/294533/33 "2005-03-19T03:32:13Z")
> [@WhyNot](#): > > I seem to remember that the **CURVE - 20 MPH** signs on Lake Shore Drive are yellow. Does that mean 20 is just a suggestion and we’re legally able to go whipping around the corners at 45? (Most of us natives actually do more like 50-55, but we’ll pretend we’re going the 45 speed limit that exists on the rest of the drive…) Yes. It is a Advisory Speed sign. Also, those you see on the interstate off-ramps “RAMP SPEED 30mph” are the same. They are suggested speeds based on the geometry of the roadway (degree of curve, super-elevation of the lane) as well as such things as the friction/traction of the pavement. ---
**Author:** ![aerodave](https://avatars.discourse-cdn.com/v4/letter/a/f08c70/32.png) [@aerodave](https://boards.straightdope.com/u/aerodave)\ **Post date:** [March 19, 2005, 4:29am UTC](https://boards.straightdope.com/t/when-do-speed-limits-take-effect/294533/34 "2005-03-19T04:29:01Z")
Knowing where a speed limit takes effect can become a problem when turning onto a road with a changing speed limit. You turn onto a road you don’t know well. Its speed limit is 35, but you have no way of knowing it because there haven’t been any signs yet. You cruise along at 40 or so, unsure of the actual limit. Then you see a sign down the road a ways (great visibility, and you’ve got good eyesight, so it’s maybe up to half a mile away.) It says 55 mph, and you think to yourself “Oh, this road must be 55 mph!” Feeling a little sheepish, you accelerate thusly. Now you’re really speeding, and the cop coming the other way busts you. Bummer. Since the 55-mph sign was the first sign you had the opportunity to see, shouldn’t it be the one in force from the moment you can make it out? After all, you had _no way_ of knowing any better. And if that rule applies to drivers who just turned on the road in that gray area, it needs to apply to all of them equally. Now we’re on a slippery slope. ---
**Author:** ![elfbabe](https://avatars.discourse-cdn.com/v4/letter/e/b782af/32.png) [@elfbabe](https://boards.straightdope.com/u/elfbabe)\ **Post date:** [March 19, 2005, 7:05am UTC](https://boards.straightdope.com/t/when-do-speed-limits-take-effect/294533/35 "2005-03-19T07:05:27Z")
> [@picker](#): > > Rosendale is a notorious little town right on the only straight shot from Madison to the Fox Valley/Appleton/Green Bay area. Ooh boy. A friend of mine got a HUGE ticket there last summer… ---
**Author:** ![Ludovic](https://avatars.discourse-cdn.com/v4/letter/l/7ab992/32.png) [@Ludovic](https://boards.straightdope.com/u/Ludovic)\ **Post date:** [March 19, 2005, 8:43am UTC](https://boards.straightdope.com/t/when-do-speed-limits-take-effect/294533/36 "2005-03-19T08:43:14Z")
> [@WhyNot](#): > > I seem to remember that the **CURVE - 20 MPH** signs on Lake Shore Drive are yellow. Does that mean 20 is just a suggestion and we’re legally able to go whipping around the corners at 45? (Most of us natives actually do more like 50-55, but we’ll pretend we’re going the 45 speed limit that exists on the rest of the drive…) While my understanding is the same as many others that have posted in this thread, namely that in many jurisdictions it is indeed a suggestion and not enforcable, I do have one warning. If the speed limit is, say, 45, and a curve on that road is not safe at speeds _above_ 45, the highway department will not put a yellow and black sign saying “curve limit 45 MPH”. Now, this may seem off topic and obvious, but it may come as a surprise when you are going 55 MPH around an unmarked curve in a 45 MPH zone 🙂 … thankfully I never had to learn this the hard way. ---
**Author:** ![Nic2004](https://avatars.discourse-cdn.com/v4/letter/n/4491bb/32.png) [@Nic2004](https://boards.straightdope.com/u/Nic2004)\ **Post date:** [March 19, 2005, 4:10pm UTC](https://boards.straightdope.com/t/when-do-speed-limits-take-effect/294533/37 "2005-03-19T16:10:10Z")
> [@aerodave](#): > > Knowing where a speed limit takes effect can become a problem when turning onto a road with a changing speed limit. > > You turn onto a road you don’t know well. Its speed limit is 35, but you have no way of knowing it because there haven’t been any signs yet. You cruise along at 40 or so, unsure of the actual limit. Then you see a sign down the road a ways (great visibility, and you’ve got good eyesight, so it’s maybe up to half a mile away.) It says 55 mph, and you think to yourself “Oh, this road must be 55 mph!” Feeling a little sheepish, you accelerate thusly. > > Now you’re really speeding, and the cop coming the other way busts you. Bummer. > > Since the 55-mph sign was the first sign you had the opportunity to see, shouldn’t it be the one in force from the moment you can make it out? After all, you had _no way_ of knowing any better. And if that rule applies to drivers who just turned on the road in that gray area, it needs to apply to all of them equally. Now we’re on a slippery slope. Ther are indeed many “What if…” scenarios and this is a legitimate concern. The posting of Speed Limit signing varies a bit per Agency or State. Typically, the spacing in based on speed on the road, nature of the section (rural or urban) and number of intersections and their spacing. We always tried to ensure that there was a posting immeditaly viewable to vehicles entering a road way from any intersection of signifigant volume. As soon as you turn on to it, there should be a posting within a short distance to inform of the speed before acceleration. This is mostly a matter of judgement for the maintaining agency and in a situation like you describe, there is a good chance that you may be able to beat it in court if you can establish that you are unfamilure with the road section. By this I mean, if you live on the side street just turned off from, it may be hard to convince a judge that you had no way of knowing the posted speed. However, if you turned off a major intersection and you are out of town and have pictures/ distances to the first posting you may get it thrown out… assuming you were not doing 70 in a neighborhood, a place were common judgement should have indicated a more appropriate speed. Regardless of these possible combinations of events, it takes effect AT the sign in every jurisdiction I have ever heard of. [Previous page](https://boards.straightdope.com/t/when-do-speed-limits-take-effect/294533.md?page=1)