You can find the last bridge for the under the radar achievement in GTA 4. Follow the simple steps below
Backtrack to all of the bridges in the game and fly under them and check its progress, if unchanged you’ve done that one and must continue trying just check every so often.
Ask friends to help you and tellthem about everything you remember about that achievement as they may provide valuable information on what to do.
Get in random fights with the cops and high-jack an airplane or use the cheat code to spawn a chopper and just keep running at every bridge if possible.
Lastly-Check your achievements you may have this achievement but just missed its rewarding and think you never got it.
Note
- Act as a low flyer-Being on the lowest position possible is helpful cause the lowest position is usually near a bridge
- Cops may shoot you out of the sky so be sure to have your phone out at all times
- Getting pedestrians mad before take-off may make them chuck you out of your vehicle before you can fly off-if this happens just shoot your gun this will work around 85% of the time if its not a cop
- Listen for that beeping-Beeping usually means youre about to crash due to repeated damage by gunshots or rams
- Watch your surroundings-you will never know when you are about to hit something if youre getting chased by coppers
