  Bus factor is a metric that identifies how resilient is the project to the
sudden engineer turnover. It states the minimal number of engineers that have
to be hit by a bus for a project to be stalled. Even though the metric is often
discussed in the community, few studies consider its general relevance.
Moreover, the existing tools for bus factor estimation focus solely on the data
from version control systems, even though there exists other channels for
knowledge generation and distribution. With a survey of 269 engineers, we find
that the bus factor is perceived as an important problem in collective
development, and determine the highest impact channels of knowledge generation
and distribution in software development teams. We also propose a multimodal
bus factor estimation algorithm that uses data on code reviews and meetings
together with the VCS data. We test the algorithm on 13 projects developed at
JetBrains and compared its results to the results of the state-of-the-art tool
by Avelino et al. against the ground truth collected in a survey of the
engineers working on these projects. Our algorithm is slightly better in terms
of both predicting the bus factor as well as key developers compared to the
results of Avelino et al. Finally, we use the interviews and the surveys to
derive a set of best practices to address the bus factor issue and proposals
for the possible bus factor assessment tool.
