It may not always be convenient but is it possible to find a "regular" taxi driver who does have seatbelts in the back of his taxi? Like I said, it won't always be convenient but you might be able to book ahead a particular driver so you know you could strap the baby's capsule in. Otherwise, wedging the capsule on the floor behind the driver would be the next best thing.

I know the speeds are reduced but unfortunately it doesn't take much speed for nasty injury to occur. Its also a fact that you simply can't hold onto an unrestrained child in an accident, and neither would you be able to do anything to prevent your own body from potentially injurying the child if using a baby carrier. Scary footage that I saw recently (I'll try to find it, although its nightmarish stuff) basically proved that you would be incapable of holding an unrestrained child before you even left the car park.