The speed limit on Route 3 is 55. The speed limit used to be 60. It was raised to 60 over 40 years ago when a study found 55 was too slow. There was never an engineering study supporting a reduction back to 55. It was reduced by executive order in 1973 to comply with the national speed limit. When the national speed limit was repealed in 1995 the highway commissioner ordered the low limit retained because he was afraid the state would be sued or otherwise embarrassed. So the speed limit is known to the transportation department not to be about safety.
It gets better. Route 3 was completely rebuilt a decade ago. The design speed for the project was 110 km/h (68 mph). The design speed is like a warranty: nothing in the road design requires a driver to go slower than 68 mph, not even on a wet road at night (the design conditions).
The average speed is not far from the design speed. The 85th percentile speed, which is supposed to be used for setting speed limits, is around 75 mph. A little over by my measurement, which found 1% compliance with the speed limit.
Eventually the absurdity of the 55 mph speed limit sunk in and in 2006 MassHighway traffic engineers recommended a speed limit increase. State Police vetoed the change, preferring the 99% violation rate that let them write tickets at will. Police have no legal role in setting speed limits. Somebody in the Romney administration weighed the risk of losing ticket revenue against the risk of being blamed for accidents. Police won. [Emphasis added.]
In this day and age, anyone who claims that the absurdly low speed limits generally found across America are about safety is either ignorant, stupid, or lying. Most highways are designed to be traveled safely at high speeds (and even most roads and streets have unnecessarily low speed limits), and cars made in the last 20 years or so are quite capable of handling well at high speeds, even under adverse conditions.
So, if you want to know why speed limits seem artificially slow, all you have to do is follow the money.