It used to be that having no police powers, the NTSB had no direct authority to shut down or control entry to anything other than the wreckage itself, and the trackage under it or in close approach to it. To shut down tracks not involved, or an entire facility, or to interfere with peripheral work by the railroad that does not affect the preservation of evidence, such as clearing un-involved equipment, building shoe-flys, using other un-involved trackage for revenue service, etc; seems a bit out of line to me.

However, I do know of at least one case where the CPUC requested the NTSB's help after a series of derailments on a rail transit line in California. And when the NTSB showed up shortly thereafter, they found some employees they thought were trying to remove evidence. This even though neither the non-derailed cars nor the wreckage were yet cleared out of their way. Not Cool!

Soon after that, federal marshals showed up (as requested by the State), and forcibly removed these individuals from the site, and then secured the area with a police line for several days. But still, they did not close adjacent tracks. As I understand it, a couple of these individuals (the supervisors) were subsequently forced to retire or be fired. For that cause or some other reason I do not know.

Maybe this sort of thing has become more prevalent for one reason or another - or maybe the feds have become much more arrogant and over-zealous in the last few years, as has the entire rest of the federal government; and as have some police agencies and especially police-like wanabe agencies, which might now include the NTSB.

Or just maybe - just maybe, it was the railroad / transit agency that decided to shut it all down, and delay getting the black box. All I know is that in my experience, when I occasionally got assigned to a railroad's forensic investigation team, we went immediately and got all the evidence we could find, especially event recorder evidence, as quickly as we possibly could, even if that meant quickly donning protective gear or shoring up the wreckage first. We went wherever the trail of evidence took us, just as fast as we possibly could.

Of course we then faithfully protected that evidence and shared it with the NTSB as soon as they were ready to receive it - assuming they even showed up; which sometimes in low profile cases, they never did; relying solely upon us to gather the field evidence.

If they did show up, we then remained on scene and assisted them anyway we could, until the all field work was complete. In those years, those of us so involved all had a good relationship with the NTSB and state regulatory agencies. Nothing specific ever happened that I know of to change any of that.

Nor did I ever know of any case where a company or transit agency was not fully cooperative and cordial with them, except maybe the case I mentioned above - though I doubt it. But I retired five years ago, and things like that may have sadly changed. Maybe in some cases, a tougher stance on the part of the NTSB is justified - or not. But I can not speak on that now.