A sweeping proposal to overhaul New York City’s subway and improve the broader transit system is expected to cost more than $19 billion, according to two people who were briefed on Tuesday, and goes far beyond the emergency repair plan that was unveiled last summer after the subway fell into crisis.

The proposal by the subway’s new leader, Andy Byford, will be announced on Wednesday in a highly anticipated presentation before the Metropolitan Transportation Authority’s board.

Mr. Byford has warned that the subway needs major upgrades to reverse its precipitous slide and the work will require short-term pain for millions of subway riders. His plan will focus on speeding up the rollout of a new signal system to replace the subway’s current antiquated equipment, according to the two people who were briefed on the plan on Tuesday and did not want to be identified because they were not authorized to discuss it publicly.

Mr. Byford wants to install new signals on significant parts of the system over the next five years, the people said. That is a far shorter timeline than previous estimates from subway officials who have said that modernizing signals across the system could take nearly 50 years. The existing signals break down on a regular basis and some are so old that replacement parts are no longer manufactured.