The original scheme for handling cars through the Grand Forks yard was to classify all arriving cars using a local switcher, including those cars destined for the local industries at Grand Forks. A separate switching operation would then deliver them. This seemed to work well when there were only a few trains through the town each day, but with the recent additions of Carson and Curlew and their extra industries wanting more cars, this approach has broken down. More details of the first attempt at operating using that scheme can be found in the article “First Attempt at Grand Forks”. Suffice it to say that it did not go well due to the extra traffic to be handled through the Grand Forks yard. So, what to do instead? Time for some serious rethinking of the process, and a bit of detailed analysis.
If we assume that the primary goal of many layouts, including this one, is to switch the industries, then one test of how successful a train operating scheme is might be to see what percentage of switching moves actually involve the industries, versus just moving cars about in a yard.
To find out, additional instrumentation was added to the program and the studies were re-run for 30 days. The percentages of all switching operations that take place at industries, staging tracks, and general yard tracks were calculated for both the original pre-Curlew configuration, and again including Curlew with the massive classification work at Grand Forks. Surprisingly, the results were almost identical in both cases. Industries were switched about 22% of the time, staging tracks also 22%, with the remaining 56% being switching entirely within a yard, mainly classification. This means that more than half of all car movements occur entirely within a yard and do not involve an industry or staging. This might be OK for a layout designed to do heavy yard switching, but it is not a very good mix of activities for a layout designed for running trains and doing switching along the way.
It is interesting to note that with the addition of more industries, the total number of car moves went up as expected, but there was also a corresponding increase in the intra-yard switching moves to handle the cars en route to the industries. As more towns and industries are added, the amount of classification required at Grand Forks will also go up, quickly making it impossible to handle it in such a small yard.
An alternative operating scheme was then examined, without a classification switcher at Grand Forks, and having all trains simply switch the various industries along their routes.
The track network and timetables were changed to separate out the towns so that each is switched by only one railroad, which also necessitated some interchange of cars between the railroads at Grand Forks. Preliminary studies show that industries are now switched about 38% of the time with a similar number for staging, which is almost twice the rate as before. Switching in a yard is now down to only 24% of the time, less than half of the previous number. This is entirely due to interchanges between railroads, and could be reduced further with some judicious pruning of shipments so that we minimize the need to exchange cars.
A couple of observations are noteworthy:
1, There are virtually no through shipments selected during restaging. In a 30 day study, only one shipment of the 772 selected during restaging was a through shipment going from staging to staging. All of the others were for cars to move from staging to an industry on the layout, and back to staging. This is a result of the strategy to always try to first find a shipment that will move a car to an on-layout industry. Through shipments are a lower priority. This approach may need to be changed so that there are more cars moving across the layout for better balance.
2, The interchange tracks at Grand Forks are very heavily used, due to the random nature of shipment selection. It is just as likely to select a shipment that requires exchange as not. This requires some further investigation to see if a better strategy can minimize the exchanges, while still keeping a rich set of on-layout shipments.
In spite of these issues, removing the notion of Grand Forks as a classification yard and just running way freights to do the industry switching is clearly a better approach as it results in less busy-work switching in the yard and more focus on switching the industries.