What is the name of the truck shown in this picture?

I think Andrew Leach's answer may be UK-specific. I am in the US and have never heard them called transporters. Regionally, at least, we call them car carriers. Yes, that's two words, but there is no single-word equivalent. A Google image search for "car carrier" turns up a bunch of pictures similar to the search for "transporter lorry".

The single word is, in fact, transporter.

If you search Google Images for transporter lorry (adding lorry gets rid of VW Transporter vans) then by far the majority look like this from http://www.freefoto.com/preview/21-26-35/Car-Transporter. Note that the word car doesn't appear in the search, but does appear in most of the results.

The picture you show is a car transporter (at least in the UK...), and there is no single word for it.

It is often shortened to transporter as Andrew Leach mentions, but that also applies to other transporters, such as tank transporters, container transporters, cattle transporters, caravan transporters, and so on, so it is too generic to apply only to lorries that carry cars.

Back in the 70's when CB radio was "in" and CW McCall had his hit Convoy, the Trucker Slang for the car carrier was

A Parkin' Lot

And along those same lines:

Bull Rack = Livestock carrier
Sand Box = Dump truck
Salt Shaker = Snow plow
Garbage Hauler = Refrigerated truck for carrying perishables
Cheese Wagon = Schoolbus

Here's what Google Images search says for your image. (However, I'm located in Montreal; it may skew the results.)

Best guess for this image: auto carriers