TransCanada Corp. is expecting to spend C$2.4 billion ($1.9 billion) for the next forecast stages in the evolution of its supply collection network in Alberta and British Columbia (BC), Nova Gas Transmission Ltd. (NGTL).

The program would add inlets for 620 MMcf/d and outlets for 1 Bcf/d in 2019-21, TransCanada said in its 2017 year-end financial results issued on Thursday.

The commitment raises to C$7.2 billion ($5.8 billion) the currently anticipated investment in NGTL’s annual construction programs to adapt to evolving markets and shifting production patterns in Western Canada.

The 2017 program completed C$1.7 billion ($1.4 billion) in additions, primarily to serve growing production from the Montney Shale hat straddles northern BC and Alberta.

Construction last fall temporarily cut NGTL traffic by 2 Bcf/d, causing brief but steep drops in spot sales and prices.

Regulatory approval is being sought for 2018 installations, titled the NGTL Saddle West Expansion, which as proposed would raise the network’s capacity by 362 MMcf/d as of 2019.

Construction also is underway on a C$100 million ($80 million) project called the Sundre Crossover, to add 230 MMcf/d of capacity by April for southern Alberta NGTL legs to fill export pipelines to the U.S. Pacific Northwest and California.

NGTL in January predicted a surge of northern shale gas would reach California, Oregon and Nevada this spring after Sundre Crossover construction was authorized by the National Energy Board.

Total gas flows on the NGTL network currently run at about 15 Bcf/d. The annual construction programs — a fixture of the grid’s evolution since its 1950s birth — are often service changes to adapt to shifting geographic production patterns, rather than overall traffic increases.