I'd like to know when is it legal to make a U turn on a 2 way street?

Other answer:

shimi:
It appears you are in the New York City metropolitan area of New York State, USA. If that is true, this is from the New York State driver handbook:
You can not make a U-turn near the top of a hill, a curve or another place where other drivers can not see your vehicle from 500 feet (150 m) away in either direction. U-turns are also illegal in business districts of New York City and where NO U-TURN signs are provided. You can never make a U-turn on a limited access expressway, even if paths connect your side of the expressway with the other side. In addition, it is prohibited for a vehicle to make a u-turn in a school zone.
oklatom:
It is legal where it isn't prohibited and safe to do so meaning the way is clear.

Easier to make a left turn at the next intersection and 3 rights, Or 3 rights and a left.

Pilsner Man:
This is in Idaho… U-Turns : U-turns are not legal everywhere, so first look for
prohibiting signs. When making a U-turn near a hill or curve, the
law requires that you be able to see 500 feet in either direction. Uturns
are prohibited in no-passing zones. Stop and yield to all
traffic before completing a U-turn.
logicalgal:
In most areas, it is only legal to make a U-turn at an intersection, BUT not where there is a traffic light or a prohibitive sign.
efflandt:
The first rule would be only when it is safe to do so (no traffic coming, in case you don't make it in one swing and need to back up). In my state it is illegal to make a U-turn mid-block in a business district or at a controlled intersetion. But I don't know if a controlled intersection includes traffic lights or just if an officer is directing traffic.
Snippeh:
Laws vary by country/state and this is an international website, you need to specify where you are for an accurate answer.
In the UK, it's legal unless it is unsafe to do so or if there are signs or road markings prohibiting it.
S:
don't U turn go to a drive way and turn around.
STEPHEN:
When there is no law against it and it's safe to do so.
Thato:
Depends on what state you are in. Here in Nebraska, when there is a no u-turn sign, or when it will interfere with other traffic it is illegal.