Designing traffic signals at locations along old streets can be a special challenge for traffic signal designers.  In a recent project on San Carlos Avenue, in an area that the utility maps showed no conflicts, the contractor hit multiple conflicts.  A
About a foot below the surface looked like the top of an old retaining wall.  The contractor was curious and kept digging, and about two feet below that hit what looked like the top of another old retaining wall.  (The boot visible in the picture is on top of this second wall.  Digging a little farther, the contractor found what appeared to be the top of an old concrete storm drain pipe, even though the (newer) storm drain inlet was about 15 feet or so from this hole.  

Life can be interesting!