Grain prices and grain traffic levels are not always an apples/apples comparison. The BNSF "sells" priority slots within their schedule in advance to avoid equipment shortages and/or elevator congestion. A Co-op can sell for X-price and ship at a time when the price can be much different months later. In this (eastern WA) area, the grain traffic is at least 95% export, with destination symbols of Rivergate, Vancouver, Kalama, Aberdeen, Tacoma, and Interbay (and even Pasco where it can be a rail/barge/boat movement). The only "feedlot" destinations currently are at Plymouth and Wallula with an occasional Nor. Cal. routing down the OT. When (or IF) the several planned ethanol plants in the local area open up, we'll see at least as much grain traffic through here, but more of it (especially the corn) might end up stopping short of the ports.
There do seem to be spikes in traffic levels that probably lag a month or 2 behind a price peak--plus there is almost always a post-harvest rush in the fall and a pre-harvest elevator clearing "dump" in the summer. A quick look at some recent lineups show an average of 8-9 loaded trains per day with about 3 off of the MRL. There are also the clay trains to the Port of Vancouver off of the west end of the DM&E or the Greybull area (2-3 per week) that use big hoppers that obviously don't carry anything edible.