That’s… actually a question that’s hard to answer in one sentence. It’s called the Dock+Go, which, going just by the name, could really be anything from an old-school iPod dock to a bike-share system. It is, as you can plainly see, neither of these things, nor does it sit anywhere in the middle ground of expectation.
That’s not a trailer, at least, not in the conventional sense. As the name suggests, the caboose is ‘docked’ to the car – although, worryingly, Rinspeed says it’s “strapped like a backpack” on existing vehicles. That sounds… safe. Especially when you consider that the strap-on (stop sniggering up the back) is actually powered (if you keep sniggering, you will be ejected from the classroom) and provides juice (that’s it; get out) to the electric battery in the car. Luckily, it does seem to actually use bolts, which, apart from being much more confidence-inspiring, also opens up a new avenue for bolt-on jokes.
Oh, and it’s also an optional extra. See, there’s the ‘space pack’, which comes with just empty space to fill between the axles, and the ‘energy pack’, which… well, packs an engine in there. The idea being that you could buy a pair of bolt-ons (cheque please), with one as a range extender and the other purely for haulage.
So, in one sentence, the Dock+Go is a possibly range-extending, volume-expanding, load-increasing clip-on for electric city cars that don’t have a whole bunch of… well, any of that to begin with. There, nailed it.