49 CFR §831.30

1. (a)Scope. The NTSB is responsible for the investigation of selected highway accidents (e.g., collisions, crashes and explosions), including at railroad grade-crossing accidents. Such investigations will be conducted in cooperation with the designated authorities of the state or local jurisdiction in which the accident occurred.
2. (b)Authority to examine or test. Pursuant to § 831.9 of this part, a credentialed employee of the NTSB is authorized to examine or test any item, including any vehicle, part of a vehicle, equipment, or contents of any vehicle or equipment involved in an accident subject to the NTSB's authority. Examination or testing will be conducted—
   1. (1)To the extent practicable, so as to not interfere with or obstruct the transportation services provided by the owner or operator of a vehicle or equipment; and
   2. (2)In a manner that preserves evidence relating to the transportation accident, in cooperation with the owner or operator of the vehicle or equipment, and consistent with the needs of the investigation.
3. (c)Any Federal, state, or local agency that conducts an investigation of the same highway accident the NTSB is investigating shall provide the results of its investigation to the NTSB.