Before leaving home on a trip, he has an obligation of intimacy with his his wife.
This obligation can conflict with the prohibition of intimacy when the onset of nidda is expected (עונה).
Sources: Yevamot 62:b; Hatam Sofer YD 170:170 and 179′ Aruch ha-Shulchan 184; Shevet ha-Levi 1:71, 3:120, and 2:209; Orach Hayyim 454:19.