Friday, January 29, 2016

Salt, plow, or do nothing?

Last week we had a reminder of what an inch of snow can do at the wrong time. But how should a city decide when and how to act to avoid unsafe roads?

Modeling what will happen is tricky. The Washington Post link mentions that they get information from the "High-Resolution Rapid Refresh" weather model, which they say typically does well for short-term storms. They also cited a concern by city officials that low temperatures would result in the brine application freezing instead of keeping the roads ice-free. This means that the physics-side of the problem is tricky to figure out.

In addition to predicting what different snow-removal solutions would do, cost plays a role. Salting in some ways is preferable since it can be done ahead of the storm, but it depends on an accurate estimate of not-too-much snow falling. Plowing on the other hand requires you to wait until snow has actually built up, but then you know with certainty how much snow there is (taken to the extreme, the city of Ann Arbor does nothing until it stops snowing).

There do not seem to be comprehensive models which do the optimal tradeoff between the cost of accidents and lost productivity and the cost of snow removal. One could argue that a policy like Ann Arbor's makes the most sense since discouraging drivers in bad weather limits the number of accidents. But that only works if people are able to stay home, which is only sometimes true. If snow falls after people have already driven to work (which is frequently the case for these public failures), doing something so they can get home safely becomes much more important.

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