The design will include a possible construction of a subway station in Monumento.
Mendoza said the Department of Transportation and Communications (DOTC) has hired a consultant who will submit the project design before the end of this month.
The bidding process for the project will immediately follow after the design has been submitted.
Mendoza said the MRT extension project could cost some US$200 million in civil works alone because of the construction of a subway in Monumento.
The subway, he said, would be constructed at the targeted connecting point of the MRT-3 and LRT-1 in Monumento for the grand plan of connecting all of Metro Manila’s railway systems.
"Kasi ang gagawin natin dito ay gawing grand station ang Caloocan. The Northrail, Southrail, MRT-3 and LRT-1 will meet there," he said.
Once completed, the project will extend the existing MRT-3 line to Monumento in Caloocan from the current end-station on North Avenue in Quezon City.
The extension will then link MRT-3 to the LRT-1 via the Monumento station.
The MRT-3 is currently linked to LRT Line 2 (LRT-2) via their respective stations in Cubao, Quezon City.
A pedestrian link, on the other hand, connects the LRT-1 to the LRT-2 via the Doroteo Jose station.
The ongoing-NorthRail project starts in Monumento going to Malolos City, Bulacan while the SouthRail also begins in Monumento going to Calamba, Laguna.
Meanwhile, officials of the MRT and LRT announced yesterday there would be no trains operating on Holy Thursday, Good Friday and Black Saturday.
This would give way to normal maintenance work on the coaches as well as on signaling, communications and automatic fare collection equipment.
Operations resume on Easter Sunday.