In GTA V, there are a total of 50 Under the Bridge Aerial Challenges. In order to earn the "Close Shave" achievement or trophy, and earn 100%, you need to fly under all 50 bridges.
Below you will find a map of the locations, and below that there is a video showing the under the bridge locations.
Here's a map of the Under the Bridge locations: (click the map below for the full size)
And here's a video showing how to get them all:
Video timeline:
Location #1 - 0:05
Location #2 - 1:14
Location #3 - 1:31
Location #4 - 1:54
Location #5 - 2:13
Location #6 - 2:32
Location #7 - 2:50
Location #8 - 3:10
Location #9 - 3:26
Location #10 - 3:45
Location #11 - 4:02
Location #12 - 4:19
Location #13 - 4:36
Location #14 - 4:52
Location #15 - 5:09
Location #16 - 5:27
Location #17 - 5:40
Location #18 - 6:02
Location #19 - 6:17
Location #20 - 6:36
Location #21 - 6:54
Location #22 - 7:13
Location #23 - 7:29
Location #24 - 7:46
Location #25 - 8:06
Location #26 - 8:26
Location #27 - 8:45
Location #28 - 9:01
Location #29 - 9:18
Location #30 - 9:37
Location #31 - 9:59
Location #32 - 10:18
Location #33 - 10:38
Location #34 - 10:57
Location #35 - 11:18
Location #36 - 11:41
Location #37 - 12:00
Location #38 - 12:23
Location #39 - 12:38
Location #40 - 12:56
Location #41 - 13:16
Location #42 - 13:32
Location #43 - 13:48
Location #44 - 14:05
Location #45 - 14:22
Location #46 - 14:40
Location #47 - 14:58
Location #48 - 15:16
Location #49 - 15:34
Location #50 - 15:54
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