Line 31 may refer to:
Line 19 (Hangzhou Metro), known as Line 31 during planning. Line 31 (Beijing Subway)
Zurich trolleybus line 31, a trolleybus operated between Kienastenwies and Hermetschloo in Zurich, Switzerland Line 31 (IndyGo), a bus route operated on U.S. Route 31 in Indianapolis, Indiana, US
See also
S31 (disambiguation)#Rail and transit, railway lines numbered S31 S31 (disambiguation)#Roads, roads numbered S31 31 (disambiguation)#Transportation, bus routes numbered 31 List of highways numbered 31