A Montreal, Maine & Atlantic Railway train derailed July 6 in Lac-Megantic, the TSB of Canada said in a release Friday.
The derailment killed at least 38 people; 12 people are still missing and presumed dead.
The TSB said it has issued two urgent Safety Advisory Letters to Transport Canada so far in its investigation into the incident.
The first letter has to do with the securement of equipment and trains left unattended, the TSB statement said.
"The TSB investigation has determined that the braking force applied was insufficient to hold the train on the 1.2 percent descending slope, and is asking TC to review the Canadian Rail Operating Rules 112 [Securing Equipment] and the related railway special instructions to ensure that equipment and trains left unattended are properly secured in order to prevent unintended movements," the statement said.
The second issue concerns trains carrying dangerous cargo -- the 72-car train that derailed was carrying crude oil.
"Given the importance of the safe movement of dangerous goods and the vulnerability of unattended equipment, the TSB is asking TC to review all railway operating procedures to ensure that trains carrying dangerous goods are not left unattended on a main track," the statement said.
Meanwhile, the TSB investigation is still in the evidence-gathering phase, a TSB statement issued Wednesday said.
"A rotating team of up to 20 experts on site continues to gather information, documenting the accident site, examining the locomotives and tank cars, interviewing company officials and witnesses, and collaborating with other partners on scene," the statement said. "This is a very complex investigation. We have had limited access to the site for safety reasons. We expect this situation to change soon."