英语从句分析the closest things we have to pulic transportation are

The closest things (主语) we have (定语从句,修饰closest things) to public transportation
（介宾短语,作定语,修饰前面的closest things）are（系动词） tourist and school buses.
（表语）
我们对于公共交通最关切的事情,是旅游车和校车.