I've heard of such vehicle, but never seen one myself.
Most Helpful Girl
I've heard of them too, they are known as GLT (Guided Light Transport), or TVR (in French - Transport sur Voie Réservée).
They are produced by Canadian transportation company "Bombardier".
These vehicles can run on conventional road surfaces or a dedicated track (guideway).
Here is the Bombardier GLT vehicle operating on a single rail track: ymtram.mashke.org/.../nancy21550.jpg
But here, you can that the vehicle is able to drive on a road, without any guideway, just like a trolleybus: ymtram.mashke.org/.../nancy21600.jpg2
Most Helpful Guy
Yes, I have, it's called Bombardier GLT (Guided Light Transit).
As far as I know, these vehicles are currently used only in French city of Nancy.
Basically, it's a dual-mode/road-rail vehicle, capable of moving both on rails and road, a pure combination of Tramway and Trolleybus.
The vehicles are guided by a central guidance rail, they ride on rubber tyres, not on rails, however, the rail does not support the vehicle, and the actual wheels which are as independent as those of a regular Trolleybus.
Unlike Trams, GLT vehicles have a steering wheel, they are capable of being steered and operating independently of the guidance rail, just like a standard Trolleybus. Anyway, steering wheel is not used when following a guidance rail (Tramway mode).
Essentially, it's a composite of rubber-tyred Tramway, and rail-guided Trolleybus, as you can see in the video.