  Public transport is vital for meeting people's mobility needs. Providers need
to plan their services well to offer high quality and low cost. Optimized
planning can benefit providers, customers, and municipalities. The planning
process for public transport involves various decision problems, such as
vehicle and crew planning. These problems are usually solved by providers. More
and more studies suggest that integrated solution approaches for these problems
are better than sequential and iterative ones. Integrated optimization of
multiple planning phases allows more flexibility in planning, which can reduce
operational costs and improve service quality. This paper reviews solution
approaches for integrated optimization using operations research techniques for
the vehicle scheduling, crew scheduling, and crew rostering problems. It also
covers some relevant related approaches from other industries. The paper
analyzes existing optimization approaches based on different aspects such as
mathematical modeling, optimization objective and method, and data source and
scope. Moreover, the paper examines the problem dimensions that are often
required in practical applications. The paper identifies some directions for
future research, such as focusing more on objectives other than
cost-minimization like robustness, schedule regularity, or fairness.
