He concluded by wishing everyone a safe trip home.

這里的by必須要翻譯出來嗎？還有是否被動語態， 他通過祝愿所有人一路平安結束？ 如何感覺翻譯別扭。

by 表示方法，conclude by doing sth 的意思是“通過做某事來結束（講話或發言）”。你的句子意思：

He concluded by wishing everyone a safe trip home.

他通過祝愿大伙回家一路平安來結束講話。

變通一下就是：他講話結束時祝愿大伙回家一路平安。

再如：

She concluded by saying she was proud to be from Salford. 她結束時說，身為索爾福德人她感到非常自豪。

May I conclude by thanking our guest speaker. 最后我要感謝大家的演講嘉賓。

He concluded by pointing out the danger of disregarding his advice. 他結束時指出無視他忠告的危險性。

I’d like to conclude by thanking everyone who has worked so hard to make this conference possible . 最后我想感謝諸位，正是因為諸位的努力會議才得以進行。