The street labels are repeated for some streets. This is because the streets are represented by several separate features, and each feature is currently being labeled. To reduce the visual clutter this causes on the map, you can remove the redundant street labels.

Checking the Street placement box makes the ESRI Maplex Label Engine merge connected features with the same label, for purposes of labeling.

When the map is redrawn the redundant street labels are removed. Some streets may still have more than one label, however, to reduce ambiguity after intersections.

On the Labeling toolbar there are two placement quality options, Fast and Best. Fast presents a quicker preview of the placed labels and is the default option. The Best option uses more complex placement calculations and places the labels in their final position.