Couple of Clarifications
My understanding is the NTSB need not be invited to a scene but rather decides whether or not to launch on their own.
See "Decision to Launch:"
NTSB Investigation Process
The Rail Safety Improvement Act of 2008 was signed into law on October 16, 2008, just a few weeks after the September 12 Chatsworth collision. The legislation not only included the PTC mandate, but changed Hours of Service, required risk reduction programs, etc. You can read about it all here:
RSIA 08
This legislation wasn't drafted in a mere 4 weeks. Rather bits and pieces of it had been floated several times during the 4-year FRA reauthorization cycle. I understand Congress was unable to find consensus between the major stakeholders so the proposals were set aside and FRA was just reauthorized for something like 16 years with little change.
Those 25 fatalities from the Chatsworth collision brought things quickly to a head.
It is interesting to note that in 1956 30 people were killed when two ATSF RDC cars overturned at Redondo Junction. Much of the carnage was caused by the windows filing and allowing ballast to enter the cars as they slid along on their sides. This was a pretty big deal at the time - I read that it was the first time such an accident was covered by live TV. Can anyone think of any laws or legislation occurring from this incident? I can't. Perhaps only 11 years after WWII or the experience of the Depression made people more tolerant of risk in those days.
Redondo Jct Accident