The decision over whether to grant planning permission for a potash mine under the North York Moors has been deferred for a third time.
York Potash has asked the National Park Authority for more time to submit environmental information.
A new date to consider the application has yet to be fixed.
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All three lanes will be open between Leeming and Catterick, without roadworks, for the first time since the project began back in 2014.
The RSPCA say they do not know what the oily substance is or where it is coming from but some birds have died from the trauma.
Project leaders continue to work towards the estimated completion date of spring 2018.