http://www.fta.dot.gov/documents/Shared_Track.pdf

says:

"
Federal Transit Administration
Final Report
Sharing of Track by Transit and Freight
Railroads: Liability and Insurance Issues
FTA-TRI-10-2005.1

5.0 Conclusions
Based on limited cases and statistical evidence, and the opinions of
knowledgeable persons in the transit and insurance industries, sharing of track between light rail and freight railroad vehicles on the general railroad system results in little or no additional risk to passengers compared to non-shared track transit operations.
"