Do the sensor rails in front of and behind the level crossing also have a function or are only the two rails next to the "barrier" observed?

Have put redstone lines under all the sensor shines. These then lead to the pistons. But of course you could also build a simple version, with only the two sensor rails in the middle, but then only the two wool blocks go up, next to which the lorry stands. In my version, all blocks are standing from the first to the last sensor rail.

Is this then still a special circuit or is the delay of the sensor rails sufficient?

The delay is sufficient, but an amplifier is needed on each side to bring the signal to the other side (at least in my circuit...).
Here's the circuit:

Simple but coooooooool

There is a better version, de with a toggle circuit works and where pistons push fences from the sides. So still no one can cross, which is not the case with the wool. A picture will follow as soon as possible.

I like it LIKE

Me too.

I like have the redstone line a little changed

cool idea

It would be much better if there was also a warning light and a notepad as a warning sound.
Idea: 8P/10P
Structure: 5P/10P
Theme adjustment 8P/10P
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Total 21P/30P: Neutral

Well, there are better!