How many? It depends on the opportunity cost of installing and maintaining whatever half baked thing (lights, sirens, computer vision, AI, barriers) it is OP is envisioning on how many thousands of bridges versus the frequency of issues it will prevent. This calculation is done all the time but not so much by the "if it saves only one x" crowd of clever solution proposers.
> whatever half baked thing (lights, sirens, computer vision, AI, barriers) it is OP is envisioning
Do you think OP should have produced a formal proposal with input from industry experts and detailed cost and risk mitigation figures before submitting a comment on an internet forum?
Either that or another ten seconds of rumination.
There's no requirement for you to be pleasant on an internet forum, but there's no reason not to be either. Snark is rarely becoming.
Large bridges like this in Europe already have lights and sometimes barriers to allow them to be closed if there are very high winds, or a vehicle collision.
Adding a system that turns the lights red doesn't seem so expensive, it existed in Denmark in 2001 when a ship almost hit the Great Belt Bridge:
Road signs and barriers, normally used to slow traffic in bad weather [1]
(Autotranslation of [2])
> The VTS system (Vessel Traffic Service) must monitor and guide the ships, so that ships approaching the West Bridge and parts of the East Bridge can be avoided. In the event of danger of hitting the bridges, the navigators must trigger an alarm in accordance with detailed rules. The most critical are two bridge sections on the East Bridge over the connection spans to the anchor blocks (each 1-2 kilometres). If a ship is heading in there - where there are no artificial islands - the alarm must be given four minutes before approaching - so that the bridge section can be cleared. On the West Bridge, the warning time is not so critical, as you can see in good time if a ship is on the wrong track. The system operates using three radars, two infrared video cameras and two photosensitive ditto plus a standard VHF antenna system (see graphic). The station is continuously in contact with all ships over 50 gross tonnes and with a mast height of over 15 metres. The ship's call number, name, cargo, destination, draft, mast height, etc. are registered on arrival at the reporting lines, and when the ship and station are contacted on VHF channel 11, the ship is automatically marked (tracked) and provided with the call number, course and speed. At the same time, the computer goes in and calculates course and speed for the next 10 minutes, which can be seen as a yellow line in front of the radar signal, which is shaped like a tuft of wool. If a ship does not want to report, goes astray or refuses to follow the VTS navigator's instructions, the VTS station disposes of one of the fleet's rejection vessels, which has the authority to give orders to the foreign masters.
[1] https://www.google.com/maps/@55.3498198,11.1018692,3a,75y,26...
[2] https://web.archive.org/web/20090116051425/http://ing.dk/art...
Out of curiosity, how much is a human life worth in these calculations?
LMGTFY:
https://en.wikipedia.org/wiki/Value_of_life
United States
The following estimates have been applied to the value of life. The estimates are either for one year of additional life or for the statistical value of a single life.
> It depends on the opportunity cost of installing and maintaining whatever half baked thing (lights, sirens, computer vision, AI, barriers)
I love how we jump to AI when all we need is 4 cameras and a dude with a pair of eyes...
Wait until you learn how train barriers worked not so long ago