Police sit in the U-turn between markers 36 and 37. Most of the time they are facing southbound, but they can occasionally face northbound. Coming south, the u-turn they use is almost completely hidden by a dense grove of trees in the median. They didn’t come after me for doing about 80 in the left lane, but anything above 75 is probably risky.

Interesting note on the recent northbound traps: recently, they have been sitting facing southbound but taking radar on the northbound lanes. When they get someone, they turn around and peel out of the median. Further north (somewhere in Hatfield) I saw such a such a trap. Came over a hill at 85 and saw the radar gun pointed squarely at me (the window was rolled down and the gun was sticking out) when I passed (but by then I had slowed to 65). Most likely had me at 80+ but no ticket. I think that, north of Deerfield, they have started waiting for people to do 85+ before pulling them over. Everyone on 91 travels so fast (the speed of traffic here is at least 75-80) and I never see anyone pulled over (but several cops in the median) until Holyoke/I-90. Best of luck!