Final answer:
A T intersection with an expressway is called a Trumpet interchange, which resembles the shape of a trumpet and allows smooth traffic flow without signals.
Step-by-step explanation:
When a side road forms a T intersection with an expressway, it is called a Trumpet interchange. This type of interchange is designed so that the side road forms the stem of the T, typically connecting to the expressway with a one-way ramp. Traffic moving from the side road is able to enter the expressway without the need for a traffic signal, and likewise, traffic can exit the expressway onto the side road smoothly, avoiding the need for stop signs or signals. It is called a trumpet interchange because the ramps and the main road typically resemble the shape of a trumpet when viewed from above.