Transportation officials took a key step toward implementing promised improvements Monday by approving a five-year, $18.3 billion capital investment plan.

The plan, which covers fiscal years 2020 through 2024, outlines about $10.1 billion in Department of Transportation projects and $8.3 billion in MBTA projects for the next half decade.

About 44% of that spending will focus on reliability and resiliency efforts, while about 29% will go toward modernizing outdated parts of the system.

Funding will also go toward long-discussed modernization projects, such as the Green Line Transformation, which will add new trains and upgraded stations along the line, and the first phase in the South Coast Rail expansion.

Following a public comment period that saw more than four times as many responses as the FY19-23 capital investment plan, the MassDOT and MBTA oversight boards voted during a joint meeting Monday to approve the latest five-year rolling plan.

Gov. Charlie Baker and other officials have often pointed to funding planned in the CIP when asked about conditions at the MBTA. The more than $8 billion planned over the next five years, they say, is a record investment for the authority.