Build It If You Can !

There are four buildings named A B C & D. They are built as shown in the picture. You are a road builder. You are given the task of connecting each building with every other such that citizens of one building can go to other three buildings. You are provided with less funds to build the road so you have to find the shortest road between the four buildings. If the Breath of the road doesn't matter. What is the Length of the shortest road possible (In miles)?

Write the answer up to two decimal places. Example:A) If it is 4 mile write it as 4.00 B) If it is 5.2356 miles then write it as 5.23