You'd be surprised how compact you can get a workable roundabout[0]. The brits have taken this to the extreme in some places,[1] Though I don't know effective a bit of paint is in actually making people treat it as a roundabout.
[0] https://media.istockphoto.com/photos/traffic-circle-roundabo... [1] https://media.istockphoto.com/photos/traffic-circle-roundabo...