Blowing horn warnings before tunnel entry?

I infrequently ride NJT into NYC, and sometimes hear the horn blow before
we enter the Hudson River Tunnel, sometimes not.

Is there a protocol or requirement for an engineer to sound his horn before
entering a tunnel? Or immediately before exiting?

Also, are any warnings needed before travelling onto a long bridge?

Thanks.

I believe the warning has to do with impaired clearances for workmen who might possibly be active at or near the tunnel entrance, and impaired visibility for the engineer about to enter the tunnel. Many, if not all, of the Hudson River and East River tunnels are protected by whistle posts, and the warning horn is mandatory in that case. I believe it's one long "in the manual."

wborys wrote:I infrequently ride NJT into NYC, and sometimes hear the horn blow before
we enter the Hudson River Tunnel, sometimes not.

Is there a protocol or requirement for an engineer to sound his horn before
entering a tunnel? Or immediately before exiting?

Also, are any warnings needed before travelling onto a long bridge?

Thanks.

There is a whistle board just prior to the North River Tunnel portals going eastward (hence the requirement for sounding the horn.) There is no requirement to sound the horn going west (exiting the tunnels) however, I always sound short series prior to leaving the tunnels in case there are workers present. The sequence is not one "long" but rather the regular two longs, a short , and a long.

Some bridges have whistle boards while others do not. Portal bridge has them both ways, while the Susquehanna River bridge only has a whistle board for northward movements.

They also do it on subways, for example, Washington, DC Metrorail requires all its train drivers to blow their whistles anytime they cross a tunnel portal either direction

Both SEPTA and PATCO sound horns before entering tunnels and when approaching a curve within a tunnel. You can hear it up on the street through the ventilation gratings.