TX AG 88 said:
as mentioned earlier they take up a lot more room. the less room they take, the slower the traffic has to go thru them.
There's a whole science to traffic flow and intersection types. I haven't studied it, but some TexAgs posters have demonstrated a high familiarity with the topic in the past.
IIRC, a certain traffic density (low) is best served by a 4 way stop. then there's a range where a roundabout performs best. Higher traffic requires at least a signal, exotic configuration (diamond, etc.) or overpass, respectively.
The evidence doesn't appear to support that.