Weekly "cars on line" data from the Surface Transportation Board's (STB) Rail Service Metrics. The STB began collecting service metrics from railroads in October 2014. As part of their submission to the STB, railroads provide data on the average (daily) number of cars on line, broken out by car type such as "box," "covered hopper," "gondola," "intermodal," "multilevel (automotive)," "open hopper," "tank," and "other." According to the STB, "each railroad shall average its daily on-line inventory of freight cars. Articulated cars should be counted as a single unit. Cars on private tracks (e.g., at a customer’s facility) should be counted on the last railroad on which they were located. Maintenance-of-way cars and other cars in railroad service should be excluded."