Seasonal Overland Travel Times

I stumbled upon Rick Stump's blog recently.  There's a lot of good stuff here!  There was a line from this post that got me thinking:

This means that if there is a good road directly between me and, oh, the market 8 miles away if I leave at sunrise (call it 6:30) and want to return home by sunset (call it 8:45) [I am using the sunrise/set times for Seaward for this time of year] then I wouldn't get to the market until about 9:30 and need to leave by 5:45.

As I've noted elsewhere [2], I'm always looking for more ways to inject seasonality into the wilderness game.  And varying travel per day with available daylight makes a lot of sense!  Taking fall and spring with ~12 hours of daylight per day as your baseline, we'd see negligible seasonal change in available travel time per day in the tropics, but even as far south as Miami, the shortest day of the year is 10 and a half hours, while the longest is around 13 and a half.  So that's a difference of 12.5%, an eighth.  Up here the shortest day of the year is around 8 and a half hours, while the longest is more like 15 and a half.  So just on the basis of having more or less daylight, something like a 30% reduction in overland travel rate in the winter and a 30% increase in the summer would be reasonable at these latitudes.  Dealing with modifying travel speed by an eighth might not be worth the hassle, but 30% certainly seems big enough to warrant consideration!  For latitudes somewhere in between Miami and Seattle, something like a 20 or 25% modifier might be reasonable and fairly easy on the math.

And then if you're already figuring seasonal overland travel speed modifiers for daylight, you could also just abstract weather into that modifier, especially if operating on scales of weeks.

One could also make the slower (winter) speed the default, and then scale everything else up accordingly, since multiplying is easier than dividing.

(Granted - this ignores historical details like the afternoon halt during summer marches.  Maybe the difference between getting 12 hours of rest in the dark and getting eight at night in the summer plus four in the middle of the day doesn't work out to that big a difference in practice.  Maybe it makes sense as just a winter penalty, where your time to break and make camp cuts into your marching daylight time.  And then there are those rascals with infravision mucking things up as usual...)