From Purses to Trailers — the Complex Challenge of Loading
Today, the True LTL blog presents its first guest blogger. Olga Raskina (see bio below) works in Operations Research at Con-way Freight, so creating models that represent various elements of our freight network is nothing new to her. Here, she compares the fine art of packing a woman’s purse to that of loading freight on a truck. Enjoy! — Sean Devine
Have you ever looked inside a woman’s purse? It’s amazing the variety of things even the tiniest of them contains. Every time I pack a different purse to go somewhere, I face the same vexing problem — how do I efficiently put everything into it so that my pile of necessary items fits, nothing breaks and the smallest items are easy to get to when I need them? My goal is to avoid that horrifying moment when I have to shake everything out on the floor trying to find my car keys.
As I was packing my purse to go to a show last night, I couldn’t help but think that this is the problem we solve every day when we load our trucks for deliveries. The problem is hard to solve quickly and optimally in both worlds. A simple approach would be to put heavy or less-used things at the bottom, put what I need often — like a cell phone — where it’s easy to reach, and always put car keys where I can see them. This is very similar to how an LTL carrier would load freight on a truck.
At first glance, it seems like this approach should work well. Which it does — except when the purse is too small to hold everything or too large to allow you to find anything quickly. Determining the best trade-off between space and ease-of-use makes the problem very complicated.
The purse-size analogy is an easy way to relate to freight operations. For example, do I load two pups or a van? If all of the freight can be loaded directly on a single-lane van, that’s the best option. If the freight will require extensive re-handling or is out for final delivery, it’s more efficient to load pups and maybe even send them on two different routes. While this small example might seem obvious, making these decisions for the entire nationwide network simultaneously can quickly become complex.
Back to the purse model — assuming I do need that box of Band-Aids at the show tonight along with everything else I usually pack in my purse, how do I decide how large my purse should be? How do I know if everything will fit? With my purse, I can take everything out and repack, which is annoying but possible. With freight on a truck, it’s not that easy.
Here are charts of my potential time to pack and find an item, and the chances of everything fitting into a sample small, medium and large purse.
You can see that as the size of the purse decreases, the difficulty to pack it grows accordingly — but so does the probability that something won’t fit. Then, once packed, the time it takes to find things actually decreases. Concurrently, the time to find something rises if the purse is packed too tightly. Which suggests two natural conclusions — it’s best to be conscious about what you really need and also determine the adequate purse size (not too small, but not too large, either) to carry it.
These, in fact, are some of the keys to efficient LTL operations as, well.
Olga Raskina is an Operations Research principal at Con-way Freight. She has been with the company since August 2009, working on analytical models to support its strategic directions. Prior to Con-way Freight she worked at the software company Emptoris, where she held the lead scientist position, leading research efforts for all the company’s products.
Olga received her Ph.D. in Operations Research from Columbia University.
