Hi,

Frankly speaking the best way to model a roundabout is to create a Civil Cell.

Try to look for tips using youtube. There are some videos about roundabouts, for example: www.youtube.com/watch

If you woudl like give me your e-mail, and i will send you my basic civil cell. (I am not sure if Civil Cell adjusted to Polish conditions will be adequate to your problem)

It will be easier to answer more exact question.

Jan Poślada