If you think you can trade when you are on journey, then it’s fine, some people will want to be alone, they will want to have full concentration if they are trading, but some people don’t care even when they are on journey, they can do their analysis even when they are not so comfortable, and they will enter trade. You can decide to trade whenever you are comfortable, or whenever you feel you can trade, I do trade whenever I like, even if am on journey I do trade as long as am not the one driving. what you should do is that just study yourself, do what you know that works for you.
If you are an experienced trader then you can do trading while on the move but those who are new to trading must think before doing this act. Trading is a risky stuff and must be handle with great care. Even there are experienced traders who need proper place and concentration to perform trading decisions. I occasionally do trading but whenever I do that I do that with full concentration while at home. I don't think I am capable to handling this risky stuff while I am on the move.
Even experience doesn't stop a trader from losing that's the more reason why you shouldn't trade while on the move because you will feel distracted along the line and you may make mistakes that will make you to encounter losses. But if you think your experience can make you to trade at anywhere without minding the risk involved then you can trade anywhere you like, personally I can only trade in a calm and comfortable place and that has got to be when I'm t home.