What data sources are available with such data to be reviewed?
Data sharing agreements would be beneficial to conduct an analysis. Availability of all data should be considered in order to support RBDM and Data Supported Decision Making.
Marjorie Collins commented
FTA's Bus Safety Data Report (2008-2018) is one high-level source of data:
FTA's Office of Research, Demonstration and Innovation (TRI) also posts reports: https://www.transit.dot.gov/research-innovation/fta-reports-and-publications
One example is a report on crashworthiness of transit buses: https://www.transit.dot.gov/research-innovation/fta-standards-development-program-crashworthinesscrash-energy-management
Another study was published by the Transportation Research Board in August 2019, "Current Practices in the Use of Onboard Technologies to Avoid Transit Bus Incidents and Accidents."
Also, this report identified factors contributing to accidents involving mass transit buses: Paul P. Jovanis, Joseph L. Schofer, Panos Prevedouros, and Koji Tsunokawa, "Analysis of Bus Transit Accidents: Empirical, Methodological, and Policy Issues," 1991
However, it would be beneficial to connect with a large bus agency willing to work with you to research these types of collisions. Typically, agency safety officers/accident investigators document the collisions and detail factors that caused the accidents. It is possible these bus agency officers/accident investigators would meet with you or possibly allow you to interview them to obtain details about the accidents.