Last summer I returned from vacation to find prominent new 35 mph speed limit signs on the exit 14 ramp off the eastbound Massachusetts Turnpike.
Curious why speed limits were posted after so many years of just warning signs, I emailed MassDOT asking for the engineering study justifying the speed limit.
First a lawyer sent me a copy of Turnpike regulations setting the speed limit to 65 here, 55 there, etc. That’s their way of saying “we don’t care, we don’t have to.” The regulation dictates a speed and they don’t feel a need to justify it.
In this case they do have to care. Their own regulations say ramp speeds are only “as posted”. So why did they post it?
Finally I got the engineering study. Only three pages, but they told me what I wanted to know.
There was a speed survey. The 85th percentile speeds were 46 “at exit”, 47 at “first curve”, and 46 “after bridge approaching tolls”. That’s all they had — no diagrams, crash analysis, etc. — but it’s enough to say approximately what the speed limit should be.
The speed limit should be 45 or 50, consistent with the prevailing speed of traffic.
The email said “based on prior accident history” the limit was reduced, but that was a bare assertion by an agency lawyer not supported by facts or law. The engineer’s report had nothing to say on the subject. MassDOT crash records show very few crashes on the ramp, and the maximum allowable reduction based on crash history is 7 mph, to 40 in this case.
I suspect some ramp crashes are in the database as mainline crashes. A thorough engineering study might have investigated that possibility.
But they didn’t do a thorough study. An engineering study has to be documented (MUTCD 1A.13 03-65) and MassDOT documents show the ramp carries 47 mph traffic safely.
The 35 mph speed limit signs are not justified by an engineering study.
This is typical for main roads in Massachusetts. Sometimes MassDOT just makes up numbers, and sometimes they collect data then set a wrong speed limit anyway. The second explains the first. Why waste time doing field work if it isn’t going to be used?
So what does this sign mean? Nothing.
It doesn’t even change the odds of getting a ticket. State Police used to ticket for “speeding” on that ramp if you exceeded the 25 mph speed posted on a warning sign. That’s a legal absurdity, but police didn’t care.
Just another bit of visual clutter to distract you from driving.
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