What feature is mandatory for temporary pedestrian channelizing barricades to ensure accessibility for visually impaired individuals using white canes?

1. Continuous bottom rail detectable 2 to 6 inches above the ground.
2. High-intensity yellow flashing beacons placed every 10 feet.
3. Rough gravel surfacing along the entire walking path.
4. Vertical timber posts spaced 8 feet apart without rails for detection.