Annotations allow you to change the heading of a diagram. Annotations are available under the Diagram Settings Box, or by clicking on the heading of the diagram. For example click on the heading area of Broadway & Middle St that you created earlier.
You will get a box that allows you to edit the heading for this diagram, the only thing that you can't change is the number of accidents. Now change Broadway to BRDWY and say OK to the box. The diagram is redrawn with the new heading. For more information on Annotations see Annotations box.