I was chatting with Martin and after some brain storming we come up with this idea.
So many answers in Travel.SE are valid for short period only, such as questions about transportation where schedules change every month or so, same for prices and routes. Another type of questions that are valid for a short period is accommodation questions where hotel prices and quality also changes over time.
My suggestion is, the moderators will have the ability to flag selected tags so answers for questions tagged with these selected tags will show a note notifying the users that this answer maybe out dated or obsolete after a certain time from the date of the last edit
Example A user (A) asks about the best way to go from A to B, another nice user (B) will answer the question with the best way and he is even so good he included schedule and prices. User (A) is happy and he/she upvote the answer and accepts it. Three months later, user (C) is traveling for the first time in his life and he is so excited, he Googles 'whats the best way to go from A to B' and the first result will be user (A)'s question. User (C) will read the information and because he is excited he will take it for granted and build his plans according to this. Poor user (C) at the day of travel he founds that the answer is obsolete and out dated so he hates Travel.SE for ever.
I know this is not the mistake of travel.SE.. but with this flagging idea things can get better, if user (C) was notified that this answer might be obsolete then he could have looked up another source and he even might update the answer with the up-to-date information.
A new tab for questions with possibility of being obsolete will be added so users who have free time can go through these answers and update it.