Under 49 CFR 217.9 railroads are required to have operational test programs that regularly check certfied engineers for rules knowledge / compliance. Recently this has been expanded to require railroads to regularly gear their tests to safety issues identified by a review of accidents / incidents. It is a pretty safe guess that Metrolink stepped up stop signal / restricted speed checks after the Chatsworth incident. The news articles stating the crew tried to stop could be the fault of imprecise reporting. Investigators have reviewed event recorder data, recorded radio transmissions, etc. and have a pretty good idea whether or not the crew was handling the train in an appropriate manner. Unlike the CPUC, this will all be presented in a public report when the investigation is complete. In the meantime unless it can be shown that mechanical failure is to blame, the crew members have a Part 240 (engineer certification) rule violation on their record and are gone for at least 15 days (30 days with the ability to be brought back after 15 if the railroad decides to and provides remedial training)

We can speculate that the brakes may have had a problem or that the passenger crew was moving at too high a speed because they assumed the opposing freight train would be in the clear by the time the passenger train arrived at the siding switch