Check this link out.
http://www.trenitalia.com/cms/v/index.jsp?vgnextoid=2aaeb5fac465a110VgnVCM10000080a3e90aRCRD over 6 years ago
You need to know that the sienna train station is NOT in the central part of the city. You will need to use additional public transport (bus/taxi) to get to the city centre. The trains are NOT always late as indicated in the previous post, but delays are not uncommon. trenitalia.it is your best source for prices/schedules. For exploring Tuscany, as a resident, recommend a rental car, unless you only plan to stick to major cities, in which case parking will be challenging to say the least. over 6 years ago