A traffic estimator is calculating the number of channelizing devices required for a 660-foot merging taper on a 55 mph highway. What is the minimum device count?

1. 7 devices, spaced at double the speed limit (110 feet apart).
2. 9 devices, spaced at 75-foot intervals along the merging taper.
3. 11 devices, spaced at 60-foot intervals along the merging taper.
4. 13 devices, spaced at the speed limit in feet (55 feet apart).