i apologize.. that intersection with a U-turn is Unsignalized.

My first response would be to ban the U-turns to eliminate the resultant
potential danger. A closer analysis should try to determine why 5% are doing
3-poiners and if they are in a certain short time period, during which a
part-time ban might suffice. Are the 3-pointers large vehicles or just
substandard drivers?

Those 3 pointers are not just because of large vehicles but the approach of
drivers to make a U-turn. As I said, the receiving lane is a single lane which
is only 19' wide. If the driver starts making U-turn immediate after the stop
line then they have to make it in 3 point but if they make a wide turn then
they make it successful. However that intersection is not that wide (approx
50') so they use most of the intersection which is a problem for other
movements.

It seems obvious that U-turns should be prohibited. Regardless of demand, it
is not acceptable to have vehicles making 3-point turns against moving
traffic. I ahve seen intersections where a pull-off area has been provided to
facilitate the turn. I do not agree with that since a vehicle is "leaving" the
pavement and thenr eentering the road. As an extreme example, I have seen
mini-jughandles created to accept U-turns. Again, I do not think this is a
good idea since it introduces another conflict point.

Why are they making u-turns? Is there an alternative - like a block to go
around? If not, and you prohibit left turns, what will they do, and is it
worlse than the 3-point turns they are doing now?

Also, are 5% of u-turners making 3-point turns, or are 5% of all traffic?

Yes there is alternatives using minor streets and go around for a block. So I
would say it is not worsen then 3-points.

Approximately 30% of total left turn vehicles make a U-turn. (Out of which 5-7%
makes it 3-point). However this condition is only momentarily during school AM
and Afternoon peak time (school start and closing time). So do you think a
complete U-Turn restriction will be justified? I doubt if there is any time
limited "No U-Turn" sign.

The AASHTO "Green Book" basically says that the design vehicle should be able
to make the u-turn in one movement, and that the combination of receiving lanes
and median width provide the necessary turning radius.

I guess that is true when you have U-Turn permitted sign at any intersection.
But what if there is no such sign.

in this case, we have only R4-7 sign and don't say anything about U-turn. While
drivers are making U-turn which I guess legal to do that.

There is no sign to permit U-turns, only a sign to prohibit U-turns. The R4-7
sign (Keep Right) is not relevant to permitting U-turns because it tells
drivers to keep right of a median or other in-road obstacle. Prohibit the
U-turns - it is dangerous to have drivers making 3 point turns against oncoming
traffic!!