+BADTFL Regional Office - Turn a bit left from yer FT arrival point, then look left up the street, prolly gonna be a fight. +Hyde Park - Turn and look at the church, typically a fight. Seems to usually be a combat, but have had non combat encounters here as well. Below you on the road shoud be an encounter, this is one that seems to proc a lot. Pike Interchange - From yer FT arrival point, look right. Move into the picnic table area, and use VATS to search for likely suspects. +Cambridge Police Station - When you spawn in from FT, go straight, then go thru the alley to yer right, turm left, and follow the road unti you see a fallen billboard. Look to the wrecked overpass, if you don't see anyone(use VATS), then move on. +Arcjet Systems - From yer FT point, turn around, and head to the statue, go to the left corner. This is one of the best spots in the game, imo, for random spawns. If you don't see anything directly under the bridge, move on.

You may have to move a bit past the wreck. +Starlight Drive In - From your original fast travel point, turn around, and look under the railroad bridge.

Some of the following is from my own experience, some are from others that I have tested. These can range from mini quests, to random treasure hints, to actual benefits to your growing community, plus coolness. Particularly due to the 4 level 4 merchants, but also in aid of seeing all the randomness FO4 has to offer, I've been gathering the following list of locations known for random encounters.

Under the bridge fallout 4