Trenton, NJ to Washington, DC buses and trains from $38

Or, see buses and trains from Washington, DC to Trenton, NJ.
Here are some trips other travelers have found on Routefriend.
2h 36m
1 stop
NJTransit Amtrak
2h 1m
0 stops
6h 39m
1 stop
NJTransit Vamoose
6h 31m
1 stop
Amtrak Vamoose
5h 1m
1 stop
NJTransit Amtrak