By Sheryl Hamlin
According to the staff report of Tai Chau, City Engineer, the following State mandate must be followed:
The California Vehicle Code (CVC) Section 22357 requires posted speed limits on collector and arterial roadways be established and justified by an Engineering and Traffic Survey (E&TS). Per the CVC Section 40802, the Engineering and Traffic Survey needs to be updated every seven (7) years for the posted speed limits to be enforceable.
Thai Chau reiterated the State mandates as found in this document which involve calculating the 85th percentile. He appeared to conflate percentages with percentiles, as does the State document, which is incorrect. Read here: Percentages versus Percentiles. A percentile is a value on a curve, while a percentage is the relation of that number to the rest of the curve. For example, a median is the point at which 50% of the data fall above and 50% fall below.
A percentile breaks down when the data set is small (less than 20), is bi-modal (two humps) or flat (no humps).
Traffic Study Recommends Increased Speed Limits
In support of the State mandate, the city hired Wildan Engineer to complete a traffic study of the city. The results are as follows. Note the increases in speeds:
Council Discussion
There were no public comments on this item. Were the neighborhoods not noticed?
Council Member Sobel, also conflating percentages with percentiles, asked if we drive faster every seven years, will the speeds increase?
Tai Chau answered affirmativly stating that there is a “natural speed limit” around the 85th percentile.
Council Member Crosswhite stated that Steckel between Main and Santa Paula is congested, has no middle line with parking on both sides and is a residential street. So why increase the speed limit?
Vice Mayor Jaurez said the street conditions are not amenable to increasing speeds.
Mayor Araiza asked why no stop sign at Bradley and Santa Paula Street? This has been the scene of fatalities. He stated that never in 30 years has he seen such results and questioned the firms’s methodology. There are so many holes in this report, he said,
Ish Cordero, Acting SPPD Chief, said the increase in the congested streets is ridiculous. Why no input from SPPD?
Vice Mayor Juarez noted that the last study was in 2014, so technically Santa Paula has until 2021 for the next study.
Rather than rejecting the entire study, which would have been appropriate in this case, the council voted to approve without segments 29,33, 12, 9 and added a stop sign at Santa Paula and Bradey.
To watch the video and/or download the staff reports, click here or here for video.
To learn more about the author, click sherylhamlin dot com
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May I suggest that this is an excellent example of why we need a County Sheriff that will quash the traffic tickets that these ‘studies” are designed to generate AT THE COURTHOUSE. A County sheriff CAN do that. I know of only one guy who WOULD do just that. At least people in Santa Paula have some theoretical ‘input” and can vote. These ‘studies” most effectively snare visitors who dontr expect lowered speed limits and dont know where the speed traps are and as they dont live there cant really complain… except NOT come to SP again..
Read the article abd go look at the streets. The traffic on most of these streets is not enough to determine a percentile. One street listed is a dead end. Would you put the speed limit at 35 mph for a two lane street with 2 schools within 300 yards of each other? Most city streets in Santa Paula are two lane and residential.
Bruce Marshall. A bi-modal set of data (two humps) may not prove accurate. The consultant did not show scattergrams of the data which would have been time (horizontal axis) versus speed (vertical axis). I would guess that in traffic patterns there would be an am hump and a pm hump. Each should be measured separately. This was not presented, so we do not know if the study was granular enough to take this into consideration.
Marshall Roath, you are missing the point. The 85th percentile is the speed at which 85% of the total volume of all cars passing down the road ALREADY DRIVE at or below. Why set an artificial limit that literally every driver is violating?
Here’s an example. It doesn’t matter which street name you choose. That hypothetical street has the actual traffic flow measured and it is determined that 85% of the total traffic volume is already driving at or below 40 miles an hour. To say that a different way, only 15% (15 cars out of 100) of the entire traffic volume measured on that street exceeds 40 miles an hour.
I ask you, what is the logic that justifies putting a 30 mile an hour street sign on that street? The only effect it would have would be to literally make almost every single car a violator. It might be great for writing traffic tickets but it doesn’t change what drivers are doing.
Studies have repeatedly shown that just simply posting an arbitrary speed limit sign is not enough to change driver behavior. People make their own judgments about the traffic conditions and the road around them, as well as their own safety and the safety of others around them, and the obvious logical thing to do is to set the speed limit where people actually drive.
What you appear to fail to understand is that changing the posted speed limit is not about increasing the speed of travel on the road. It is simply adjusting the posted limit to match what people are actually doing every single day.
I’ll give you another example. Have you ever been out on Highway 14 between Palmdale and Lancaster? Or between Palmdale and Los Angeles? The traffic through that area is averaging between 85 and 90 miles an hour. Literally the entire volume of traffic is moving that fast. If you try to just sit at 65 miles an hour you’d be run over from behind.
The drivers have a established what’ the speed limit should be there by their habits and their collective judgment for safety. Why should that road be posted at 65 miles an hour when literally no one travels at that speed?
Another question is what would change if they posted the speed limit in those areas at 85 or 90 miles an hour?
It’s a serious question. What would change if they changed what was posted on the signs? Would driving speed increase above current levels? Or would the only effect be to reduce the number violators?
What is the point of a law if virtually every single person is violating it? Is that a problem with the people or with the law? I submit that in that case it’s a problem with the law.
Why do we continue to accept mediocrity from consultants? Mayor, you stated that the study was lacking, yet voted for it. Anyone familiar with the city could recognize that residential streets with a stop sign at every block can’t have a speed limit of 30 or 35 mph. This report should have been rejected by Mr Chau before being presented to Council.