The National Energy Board has granted conditional approval to a massive Enbridge pipeline that would enable more Canadian crude to flow into the U.S.

The Line 3 Replacement project involves rebuilding a 1,660-kilometre pipeline that's nearly a half-century old and has had several ruptures over the years. The total cost is $7.5-billion, $4.9-billion of which will be spent in Canada. The remaining $2.6-billion covers the replacement program in the U.S.

It would enable 760,000 barrels a day to be shipped from Hardisty, Alta., to Superior, Wisc. Today, the aging line is only shipping about half of that.

Line 3 is one of six arteries that make up Enbridge's Canadian mainline, a key piece of infrastructure that moves Alberta crude east.

Enbridge has said it's better to replace the Alberta-to-Wisconsin line in its entirety than to fix it. It would be the largest project in Enbridge's history but has drawn less attention than other major pipeline proposals.

The NEB panel's decision comes with 89 conditions and covers the segment that runs from Hardisty, in eastern Alberta, to Gretna, Man.

There are separate U.S. permitting processes that the project must undergo before construction can begin. Regulatory wrangling in Minnesota has already delayed its planned startup by two years to 2019.

Environmental groups and Ojibwe communities in northern Minnesota have sought to stymie Line 3 -- along with other Enbridge pipelines -- through a variety of legal and regulatory means.

A higher-profile cross-border project -- TransCanada's Keystone XL proposal -- was rejected by the Obama administration in November on the grounds it would undermine U.S. efforts to combat climate change without delivering significant economic benefits.

The existing Line 3 already has a presidential permit, the approval TransCanada painstakingly sought for eight years.

Critics have argued that because the replacement project would significantly increase the amount of Canadian crude crossing the border, it should be subject to the same process as Keystone XL.