W.H. Auden wrote that in relation to a writer, most readers believe in the Double Standard: they may be unfaithful to him as often as they like, but he must never, never be unfaithful to them. Much the same might be applied when considering the question of double dating; our heads may easily justify things for ourselves that our hearts are indignant about in others. Having dealt with this issue from the angle of both toiling single and hapless shadchan, the perspective gained, along with the attending understanding of both head and heart on the issue, my position has boiled down to that very Jewish answer of: it depends.
When considering the extremely truncated timetable of Frum (right-of-center Orthodox) dating, it becomes imperative to carefully monitor one’s ability to focus on the matter at hand. In the span of a few months, you will endeavor not only to get to know, understand, and connect with a stranger, but also to lay the foundations for a life of growth and service of Hashem together. A break in concentration means overlooking important pieces of the puzzle and a disjointed, incoherent dating experience. Conversely, the stresses and rigors of everyday life may make it difficult to fit in the long parcels of time necessary to properly invest in a date, something especially complicated for those who are geographically disadvantaged, located at a distance from the main population centers of Orthodox Jewry. Double dating would seem to run counter to the former idea, splitting your concentration between multiple potential spouses, while the latter would strongly validate it as the pragmatic thing to do, helping to maximize the time available and cover more ground before ground covers you.
To mitigate the conflict between these competing needs while still allowing myself to sleep at night, my hard line is that double dating is generally inappropriate. Since we date with an eye towards marriage, the utmost respect and consideration must be afforded to your date du jour, no matter jaded you may have become. That being said, under the extenuating circumstances of significant travel, it would seem excusable to me for a single to date multiple people simultaneously for a very brief period, not more than three dates apiece. This would allow you to accomplish a significant amount of inquiry while still being able to divest from this polyamorous situation before any potential relationships become serious. I would not begrudge someone the opportunity to play the field as long as they can quickly realize when the game is starting and decide which stadium they want to attend.
Technicalities and specific guidelines aside, the guiding principle and takeaway message for this and many other questions in dating should be to act with respect and integrity towards everyone you meet, constantly asking yourself what it is that Hashem (G-d) wants from you, and hopefully this will lead us all to become R’ Hirsch’s Jew “in the synagogue and the kitchen…as father and mother, as servant and master…with one’s thoughts, in word and in deed.”