In Potlatch 2, if you want to create an intersection where two ways are crossing but, crossing, you Shift-click the intersection point and a junction node appears. I am not sure what you mean by wanting two nodes to become one. If there are nodes in each way that are at, or close to, the location of the intended junction, they may just get in the way. I would delete them either before or after you make the junction as mentioned above.

In Potlatch 2, if you want to create an intersection where two ways are crossing but, you Shift-click the intersection point and a junction node appears. I am not sure what you mean by wanting two nodes to become one. If there are nodes in each way that are at, or close to, the location of the intended junction, they may just get in the way. I would delete them either before or after you make the junction as mentioned above.