That's a good point. What qualifies as modern in my experience is a good old classic Amtrak which is powered by a full size diesel-electric locomotive front & rear. I imagine there are ways to make it to the front, but I imagine they involve catwalks on the side of the locomotive.

But, much like I am not a lawyer, I am also not a train engineer. Or even a railfan. So I am probably completely wrong.

I do appreciate Amtrak keeping TSA out, in any case.

There are still locomotive-at-the-front trains in Europe, and on these I've never noticed being able to walk through to the locomotive from the carriages.

I have found the term for the more modern type: "Multiple Unit" [0]. Smaller motors are installed on many axles, the same as a metro train. It seems they're more reliable and cheaper to run (less wear on the track due to a better distribution of weight), but I agree with the noise issue — I prefer it when I travel on a locomotive-hauled train, since the interior is close to silent.

A site like [1] has a few train interior (and exterior) photos aimed at foreign tourists in Europe, rather than railfans. [2] will get boring quickly, but shows a European view of modern intercity trains.

[0] https://en.wikipedia.org/wiki/Multiple_unit

[1] https://www.seat61.com/France.htm

[2] https://www.youtube.com/watch?v=2-u1a2WswpI