Radda in Chianti sits at the top of a hill, so there are no trains and very little public transportation, therefore you can get there either by bus or with your private vehicle.
If you come by car, there are plenty of (free) parking areas around the village, so you can leave your car there as long as you wish.
There are not so many buses that come to Radda, but they are a good option if you are staying in Siena or in Florence.
From Siena, you can take bus 125A, that costs €3,00: see the schedule here
From Florence, you can take bus 365A, that costs €4,00: see the schedule here
What to do in Radda in Chianti?
Click on the image below to be re-directed to Radda Tourist Information's website.