What do 'W/L' and 'W/B' signboards on railway tracks mean?

All of us must have enjoyed the train journey. Many of us are regular train commuters. While travelling, we must have noticed several letters and signs printed on coaches or put up by the side of the tracks. Most of us are not aware of their meanings. 

Top 50 Positive Words and Phrases – With Examples

The Best Electric Toothbrushes of 2023, Tested and Reviewed

What does W/L represents on side of the rails? - Quora

European Train Control System - Wikipedia

What do different colors of safety signs mean?

What's the W sign I see train workers hold up sometimes when a

Harvard Student Groups Face Intense Backlash for Statement Calling

All types of boards on railway tracks I जानिए आखिर यह

Maslow's Hierarchy of Needs