Mill St Belmont, MA
The headed-downhill side of Mill Street, from the McLean entrance down to Route 60, has a serious set of potholes developing. I think the roadbed underneath must keep getting washed away or frost-heaved, because this is a recurring problem. As a commuter cyclist, I've had a dangerous crash here once and several other near-misses on this set of potholes. Right now, they're more like 4-inch-tall waves in the asphalt--- if you hit them wrong on a bicycle, you're going down. The fact that this is a steep downhill makes it particularly easy to crash, because the road goes from well-surfaced to hazardous in about 100 feet--- which isn't long if you're coasting downhill at even a moderate speed.