By John Carr, NMA Massachusetts Activist
“Where’s the beef?” — Wendy’s advertising slogan c. 1984
Last time I wrote generally about the difference between public relations and engineering. This is the first of a series of closer looks.
Before trying to distinguish PR and engineering, check whether what you have is either. Many times the official statement boils down to “because I say so.” If you are reviewing a document that purports to be an engineering study to set a speed limit, start with a checklist:
- Does the study include data, or merely assert that data has been considered?
- Does the study give you enough information to suggest an approximate speed limit (within 5 mph)?
- Does the study admit to political influence?
A few years ago I asked for the engineering studies used to determine some slow speed limits in western Connecticut.
To refresh your memory, a speed limit should be within 5 mph of the 85th percentile speed of free flowing traffic, which is usually about 5 mph above the average speed. The exact speed can depend on a few additional factors. The reasons for the choice of speed limit must be documented. (MUTCD 2B.13, 1A.13)
Welcome to Connecticut, now shut up
In Connecticut the State Traffic Commission is responsible for all speed zoning, on state or local roads, but don’t go complaining to the STC about speed limits. Official policy is to ignore citizens’ complaints. Only the top politician or police officer in a town, the Local Traffic Authority (or Legal Traffic Authority), is allowed to have an opinion about a speed limit. This applies to state-owned as well as town-owned roads. If a mere citizen (or engineer) says a limit is too low it’s fingers in ears, “la la la I can’t hear you.” On the other hand, the First Selectman’s opinion goes into the engineer’s report and disagreement normally acts as a veto.
You’re better off with a police officer in charge than a politician. Many police chiefs understand the futility of posting speed limits unrelated to road conditions.
Route 133: 40 = 50
A politician from Bridgewater asked to reduce the speed limit from 40 to 30 on Route 133 south of town. The STC report said:
This section of Route 133 is a two-lane, bidirectional roadway that has an overall width of approximately 26 feet and traverses a thinly settled residential area. The existing speed limit is 40 mph and recent radar checks indicated that the average and 85th percentile vehicle operating speeds were approximately 42 mph and 47 mph, respectively. The latest available daily traffic volume was 3,200 vehicles which was recorded in 1994. The horizontal alignment consists of two curves, the most severe being 3.5 degrees which has a comfortable speed of 55 mph or greater. The vertical alignment has two grades, the steepest being 5 percent for a distance of approximately 800 feet.
An analysis of the latest available recordable three-year accident experience did not reveal any concentrations or patterns of accidents that could be susceptible to correction by a reduction in the speed limit.
The study has not indicated any significant changes since the previous study or revealed any pertinent information that could have an effect on the existing speed limit. Therefore, based on roadway geometrics, road side development, vehicle operating speeds and trial runs, it is recommended that the existing 40 mph speed limit remain the same.
Notice the passive voice in the last sentence. The recommendation apparently conjured itself out of thin air. I believe that, because an engineer would have noticed the result was bogus.
The speed limit should be close to the 85th percentile speed, so the starting point is 45 or 50 (47 rounded down or up). Other factors in the report all pointed towards a higher rather than lower limit. The curves are not sharp, the grade is not steep, the road is not busy, the area is not thickly settled, the accident rate is low. The facts voted unanimously in favor of 50 therefore the speed limit shall be 40. The magician pulled a rabbit out of his coat and held it above his hat. Tada! Did you see what was there, or what you expected?
The study found the speed limit should be 50, but the conclusion substituted 40.
The STC didn’t send me anything for the 30 mph zone to the north of the 40 zone. I learned through other channels that the 85th percentile speed north of town center is 45. Connecticut doesn’t report speed measurements when they are off by an embarrassing amount from the speed limit. Engineers feel comfortable proposing a 10 mph deviation, but not 15.
Route 67: A speed trap with seniority
After listing all the town politicians who did not want speed limits increased, the review of Route 67 stated:
The field investigation revealed there were no significant changes since the previous review and with the exception of a 35 mph zone in the Town of Oxford, it has been determined the existing speed limits are appropriate and do not warrant any revisions at the present time.
I didn’t edit out the field measurements. They weren’t in the report. This is not an engineering study. At best it is a claim to have done an engineering study. I didn’t ask whether they did a study. I asked for the study.
The claim that little has changed since the previous review is plausible. If true, it does not mean the speed limit is justified. The road had been a speed trap for 30 years at the time. People think that old speed limits are immutable features of the landscape, but they are supposed to change over the years.
So why is the speed limit 45 between New Milford and Bridgewater? I suppose to keep the police officer parked by Cortina Gardens busy. The approach is downhill both ways. It’s hard to go just 45, even on the flat parts.
These are cases where the state’s documents show there is no evidence to justify the speed limit. This is not a matter of professional judgment. There was not even an excuse offered for the choice of speed limit. The reports are on their face not sufficient to comply with rules for setting speed limits. One clearly shows the speed limit should be 10 mph higher. The other says nothing about the proper speed limit.
Let’s go over my checklist. One of these has data, the other merely asserts that there is data. The one that has data clearly indicates a different speed limit without offering any excuse for the 10 mph reduction. Both list the politicians involved in the process. Both of these studies could just as well have said “the speed limit is what it is because I say so.”