Transport Minister Troy Buswell has ruled out intervening to keep grain on rail as time runs out for Brookfield and CBH to reach a deal to prevent the closure of ageing Tier 3 lines in the Wheatbelt.
A dozen fully loaded wagons remain stranded near Quairading after a major derailment nine days ago.
The Office of Rail Safety has called for the report from a joint investigation into the incident from track operator Brookfield and rolling stock operator Watco, which carts grain under contract with CBH.
It is understood the findings will have a major bearing on who meets the huge cost of the clean up and repairs.
The Tier 3 lines are due to close on October 31 unless Brookfield and CBH can thrash out a deal to keep them open as part of negotiations on a new commercial track access agreement for all CBH grain freight.
Mr Buswell said yesterday it was up to Brookfield and CBH to keep the lines open.
"Brookfield and CBH need to come to a commercial decision to determine if Tier 3 is econom- ically viable and should remain open," he said.
Farmers in districts serviced by the lines have warned of thousands of extra truck movements if the lines close, with CBH now forecasting a better than expected harvest of 12.8 million tonnes.
Mr Buswell said the Tier 3 lines carried about 12 per cent of WA's grain. The section of track where the derailment occurred is 116 years old and use of the lines is heavily restricted because of their age and condition.