Sometimes you have to be careful what you wish for. If you're not absolutely sure that a Turbo Roundabout is (in particularly, a "turbo-roundabout" as might be implemented by TfL) and not absolutely sure that it is what you want, then don't ask for one.
This video from the Fietsberaad shows a "Semi"-Turbo Roundabout in Hilversum. It initially appears to work quite well in the video designed to promote the idea, but this is merely a "semi-turbo" roundabout and in many ways actually more closely resembles normal Dutch roundabouts. I caution to look out for where there are two lanes of motor vehicles which need to be crossed at once by cyclists and pedestrians - a case which is excluded from the video:
Youtube found the next video, which is of a simulation of a Signalised Turbo Roundabout. It shows how motor-vehicles flow nicely around the roundabout, but there is no consideration of cyclists or pedestrians in the simulation:
Indeed, the whole point of the turbo roundabout is to "improve traffic flow". Turbo-roundabouts were never intended to make things better for cyclists or pedestrians. Cyclists don't much like them. The Fietsersbond (Cyclists' Union) in the Netherlands has complained about unacceptably long crossing delay times for cyclists at Turbo Roundabouts.
As I said before, "be careful what you wish for". Why ? You might end up with something similar to what is in the next video - a real, live, turbo roundabout in Eindhoven videoed by someone who isn't trying to sell the concept. The title is "Floraplein in Eindhoven very dangerous for cyclists":
Note how crossing double exit lanes causes trouble for cyclists.
So what's the alternative ? I didn't have any photos or videos of my own to show here because we don't have turbo roundabouts in this area. In fact I've documented before what all the roundabouts in Assen look like. None are turbo roundabouts, and none cause problems for cyclists.
Some other ideas are pointed to by the website set up by people who are campaigning to improve or replace the Floraplein turbo-roundabout. It includes a link to an interesting presentation about alternatives to turbo-roundabouts written by Peter Kroeze of Ligtermoet and Partners.
When observing from afar it can be difficult to tell what really works from what does not work. We've already seen both shared space and strict liability given far too much credit for the cycling conditions in the Netherlands. Let's not add Turbo Roundabouts to the list of things that are misunderstood.
A year after posting this blog post, warning that Turbo Roundabouts, no matter how attractive the name sounded, were never intended to be used by cyclists, a story appeared about the "walking and cycling officer" of Bedford in the UK was proposing to use "Dutch experience to improve cycle safety" by building a turbo roundabout which is actually worse than the example from Eindhoven because there is to be no cycling infrastructure at all.
"Dutch" even though it is something which you would absolutely never see in the Netherlands. Frankly, it's difficult to imagine a larger mistake than this.
We run cycling infrastructure study tours precisely in order to try to help councils like Bedford to not make such expensive and dangerous mistakes as this one. Planners need to be educated. They need to learn from the best examples and not just guess at what they think best practice might be. We'd be very happy to host a contingent from Bedford if they'd like to see what the Dutch really do so that future "Dutch" innovation in Bedford can be inspired by the real Dutch infrastructure.