You just never can tell what'll strike the fancies of investors. Some years they all want the riskiest biotech or med-tech ideas they can find, other years see mining and energy as all the rage. And one of the hotter areas of today is transportation infrastructure.

We all heard a lot about the Dubai Ports World buyout of Peninsular & Oriental Steam Navigation, as numerous members of Congress simultaneously salivate at the opportunity to get in front of cameras to decry "Arab control" of some U.S. ports. And other folks might also be aware of the recently concluded battle for British airport operator BAA, in which Ferrovial beat out a group lead by Goldman Sachs (NYSE:GS).

Heck, even we here at The Motley Fool have gotten into the game. Fool buddies Seth Jayson and Bill Mann have each waxed eloquent on their favorite Mexican airport operators -- one for our international stock report Around the World in 80 Minutes and the other for our Motley Fool Hidden Gems newsletter service.

And today we learned that Goldman Sachs (along with other investors) was happy to buy a "port" -- airport, seaport ... it's all good. For British seaport operator Associated British Ports announced that it had accepted a bid from a Goldman-led consortium. The deal represents just a 4% premium to the prior day's close, but the stock of AB Ports had been trading up on the expectation of a bid -- in fact, the stock closed above the deal price, suggesting traders expect a rival offer.

Here's the thing, though. What happens when investors get excited about a sector all at once? If you said "prices go up," congratulations. The Goldman group is paying a pretty steep price for AB Ports, and my quick cash flow modeling doesn't suggest much (if any) room for disappointment here.

Whatever the case may be with that, there's no denying that transportation infrastructure is a hot place to be. Just remember, Fools, that no sector is too hot to justify ignoring sound valuation principles.

For more Foolish flights of fancy:

Want to take your portfolio beyond our own ports? Our international stock report, Around the World in 80 Minutes , can help you find some good investing ideas abroad.

Fool contributor Stephen Simpson but has no financial interest in any stocks mentioned (that means he's neither long nor short the shares).