[thechat] Speed limits in USA

Luther, Ron ron.luther at hp.com
Wed Aug 11 10:59:00 CDT 2004

Madhu Menon asked about US speed limits:

Hi Madhu!

When are you coming over?

I thought of some more things for you to be aware of:

Speed Limit signs.  These are generally rectangular white signs with 
black lettering on the right hand side of the road letting you know 
what the posted speed limit is.  They are supposed to be placed after 
major intersections and after freeway on-ramps so that 'new' traffic 
will be aware of the limit. They are clearly marked "speed limit". 

Sometimes they will give you different numbers for day or night driving 
or have a different limit for trucks.

Speed Advisory signs. We also have these 'other' signs that can be a 
bit confusing. You might be in a 45MHP speed limit zone and see a 
sign that says "30MHP Curve Ahead".  AFAIK that's only a recommendation 
and not a legal requirement.  It doesn't say "speed limit" so I don't 
think you can get a ticket for speeding if you stay at 43MHP through 
the turn.

Other Speed signs. You will also see some signs that say "Slow Children 
Ahead" or "Slow Cattle Crossing". Those signs are just plain mean. Who 
cares if those kids or calfs aren't the brightest? 

No numbers are given on these signs - which leaves them a bit open 
to interpretation.

School Zones. You might be in a 45MHP speed limit zone and see a pair 
of alternately flashing yellow lights with a "School Zone 20MHP Speed 
Limit" sign between them.  You will need to slow down for that. You 
_can_ get a ticket/fine if you don't.  Now ... if the lights aren't 
flashing, then you don't need to slow down. See how easy!  

BTW, the flashing sign _ending_ the school zone is likely to be facing 
traffic heading the other way ... so you can get stuck behind someone 
continuing to go 20MHP loooooong after the school zone has ended. Well 
planned, eh?

Other School Zone signs. Hey! Those flashing lights cost money pal ... 
so the 'newer' school zone signs look more like ordinary speed limit 
signs. They might have some verbiage saying "School Zone 20 MHP Speed 
Limit". And then, in teeny tiny letters at the bottom "8am to 9am and 
2pm to 4pm schooldays".  That means it's okay to honk your horn at 
people driving 20MHP through there at 5:30pm in the evening on your way 
home from work ... cuz the speed limit reduction is only in effect for 
the posted hours. It also makes it even tougher to figure out where the 
dang school zone ends!

Flashing yellow lights. A yellow flashing light in the middle of nowhere 
usually means 'caution - slow down' ... but there won't be any numbers 
associated with it.  Some highways waaaaaaaaay overdo this - sez Ron 
remembering a recent drive back from BFN, Texas where they had these 
at _every_ blinking blinking intersection.  [OTOH, some residential 
neighborhoods 'turn off' the traffic lights (make them blink yellow) 
after midnight or in the wee hours of the morning when traffic is light.  
This is generally a good thing.] 

Other Cool US Highway signs:
Two of my favorites ... a rectangular sign with alternating light and dark 
diagonal lines (typically black and white - sometimes black and yellow). 
There are no words at all on these signs.  This sign means "bridge". There 
is supposed to be one of these at the beginning and end of each bridge. 

Why? I dunno. 

I think they were created by rallyemasters so they could tell you to turn 
after the bridge ... cuz that steel beam structure you drove over that 
crossed the river doesn't count as a "bridge" if it doesn't have these 

Finally ... we've got another sign ... usually diamond shaped in yellow 
with a black squiggle on it. It you're lucky you'll see some of these 
while driving around. If you're really lucky you might see one of these 
with some magical "next 20 miles" words at the bottom.  This sign means 
'Look around. Make sure traffic is light. Then drop the hammer cuz there 
is a fun 'twisty bit' coming up in the road ahead.'

HTH make your US driving a bit more fun,

(Who remembers back before the US 'standardized' on colors and shapes 
for various highway signs. Who knows - maybe there is an international 
RFC on that today.)

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