Why are so many flat CA state highways signed at 55 MPH?

[heynow415]

Doesn't California have a rule that says that speed limits have to be periodically justified based on the 85th percentile' principal?   This is to help neutralize 'Deputy Dawg' speed traps.

Mike

Yes, it does, for the most part. The default speed limit on two-lane highways is 55, unless posted otherwise. Speeds can be increased to 65 or 70 based on certain criteria and typically only on divided highways or freeways, and some two lane highways designed to expressway standards.  At the other end of the spectrum, the default speed limit in business districts and on residential streets is 25; in school zones and alleys it can be lowered to 15. 
For everything else, posting an enforceable speed limit must be based on an engineering and traffic study (E&TS) to determine what the 85th percentile is and rounding to the nearest 5mph.  Based on that same study and the particular situation of the roadway, the certifying traffic engineer can reduce the 85th speed by another 5mph, such as roads with lots of driveways, blind curves or intersections and the like. E&TS certifications have an initial life of 5-7 years but can be extended up to 10 years if there have not been any significant changes to the roadway or its surroundings (configuration, traffic patterns, new development, etc.).  At that point a new study needs to be done to validate the posted speed. 

[abqtraveler]

This is something that has wracked my brain for years and I have never found a good answer.  I was thinking about this a couple weeks back on CA 138 in Antelope Valley and it came up in another thread today:

I'd say California except for where it caps out (I.e. 65 on 4 lane roads, cap of 70 on freeways). Any speed limit lower than the default must be justified by the 85th percentile (in general). While there are many exceptions (especially freeways), I'd say they're mostly good.

For other states, Arkansas and some of Texas is relatively good on the rural freeways, especially given their design. Not all parts of these states are good per se, but this is what I could come up with lol

Are you kidding?  There is so much 55 MPH two lane roads that could be bumped up to 65 MPH.  CA 43, 145 and 41 near me could all be switched tomorrow and it would just match the existing traffic flow. 

I am stupid, I completely forgot about some of the more-rural 2-lane roads.

Point changed to: California in more built-up / suburban areas. Rural areas still need a ton of work... maybe if the default was 10-15 higher?

Thanks for the catch

FWIW I've been trying to crack what exactly the code or standards Caltrans goes by for classifying two lane roads for 65 MPH speed limits.  North of Sacramento and in the desert regions they fairly common.  All the same some of them don't really make a lot of sense like the 65 MPH portion of CA 99 near Red Bluff.  I thought that it might have something to do with two lane expressway classification, but that seemingly isn't the case.

I don't know what the speed laws in California are, but I know that most states codify "absolute" speed limits for certain roadway classes into law. That means, for example, a 4-lane highway with an 80 mph design speed will only be posted at 65 mph, if the law specifies a 65 mph speed limit for that type of road.

To raise the speed limit on the road I used in my example, the state legislature would have to pass a bill establishing the new speed limit, which would then have to be signed by the state's governor before the speed limit could be increased. Out here in New Mexico, the speed limits are codified into law by the legislature, and every legislative session some lawmaker always introduces a bill to raise or lower the speed limits for certain road classes.

Now, there are a handful of states that don't specify speed limits in law (I believe Texas is one of those states). In essence, the state legislature has deferred to the engineering experts within the state department of transportation to properly set the speed limit on a given stretch of road. When it comes to getting a speeding ticket, violation of the state's speed law is based on "prima facie" evidence of speeding...in other words, traveling faster than the posted limit.

[Max Rockatansky]

Right, but that obviously isn't the case here.  That's why I mentioned some rural two-lane highways out in the boons with 65 MPH speed limits.  CA 127 and CA 45 come to mind right off the top of my head.

[ClassicHasClass]

CA 266 also.