Predicting icy road conditions
December 18, 2016 10:55 AM   Subscribe

I just watched the very informative series of videos at Icy Road Safety. It says that freezing rain is the most dangerous driving condition there is. As a new Vermonter, I have so many followup questions, some general and some specific to this winter storm...

1) I'm interested in driving from Montpelier, VT to Boston, MA (I-89 to I-93) sometime today/tonight. Is there going to be a safe window of opportunity to do this? (I'm guessing not, but...)

Right now in Montpelier it's 40F and raining, with temperatures dropping. I'm looking at New England 511 and there are freezing rain advisories all over the place, just as you'd expect. But I'm not sure what that means for the rest of the night. At 5pm it should be around 25F, dark, and overcast. At that point, what should I expect the road conditions to be? Will everything be a slick sheet of ice until the sun melts it tomorrow morning, or will crews come out and salt so that driving will be perfectly fine after it gets below freezing?

2) The big-picture question is: after freezing rain/wintry mix, when is it generally safe to drive again?

The website Icy Road Safety says to avoid driving when temperatures are near freezing (26-36F) with any precipitation coming from the sky. It doesn't say anything about what happens afterwards, and whether that changes if the temperatures are falling vs. rising, or if it's daytime vs. nighttime.

3) Vermont doesn't seem to plow or salt as often as I was used to in Boston. Many of the roads I regularly drive on are semi-covered in compacted snow, like this, with tire tracks sometimes being bare kinda-wet road and sometimes not. I'm unclear on whether it's salted (can any Vermonters weigh in?). Normally I'd be concerned about daytime snowmelt that freezes quickly as soon as the sun set, but the roads have been like this for weeks now and I haven't experienced icy driving at night (with lows around 0-15F). What's going on? Is there a lower temperature at which the daytime snowmelt will freeze, and then all of a sudden everything will be icy?

(Context: I'm a moderately experienced winter driver, but this is the first time I'm using a car as my daily transportation. I'm finding it somewhat stressful. I do have winter tires and about 100 lbs of sand in the back of my small 2WD hatchback. I don't have to deal with steep dirt roads, mostly just numbered state routes and I-89.)
posted by danceswithlight to Travel & Transportation (5 answers total) 4 users marked this as a favorite
Ice is frozen water. As long as those snowy roads don't melt (get above freezing) they will stay snow and not turn to ice. On heavily traveled roads, the cars will eventually turn packed snow pretty icy because compaction and friction melt it momentarily, especially at intersections where they spin their wheels, then it re-freezes as ice.

As far as freezing rain, the roads stay icy until it melts or is physically removed. Salt, sunshine, cars with studded tires, ice scrapers on plaws, sublimination (on a sunny day below freezing) will all help remove it but no, it doesn't go away once the rain stops.
posted by fshgrl at 11:02 AM on December 18, 2016

The temperature in Boston is in the upper 50s right now, mild and rainy. The 3-4 inches of snow that fell yesterday has melted away. The roads are wet, but all clear with obviously no ice. A cold front will be passing through later this evening and the temperature will be falling below freezing in the Boston area over night, which will cause black ice to form on roads that have not been treated. IME the Boston area is fairly aggressive at treating roads when black ice is forecast to form. So if you drove to Boston today/tonight all I can say is that the conditions should be perfectly OK down here. But I can't say that about areas further north.
posted by Seymour Zamboni at 11:11 AM on December 18, 2016

If you are in VT heading to Boston, go now before it gets icy. Roads are a slushy mess now. Especially with so much meltiness today, there will be patches of ice as stuff sets up before the salt/sand trucks have been out. Vermont should salt and sand the hell out of interstates (all night long pretty much) but there are rules about when they do it You might like to read this Snow and Ice Control plan. If you look on page 11 you can see that with some roads the plan is not to get them down to bare pavement and with some there is. Your town may have different rule-of-thumb plans for the roads that are under their control. If you're literally in Montpelier you could also just take a bus down.

Things are rarely a slick sheet of ice if it's above 20F but when it's just barely warm enough to rain but the ground is cold, that is when you get frozen rain on the roads and that is treacherous before the trucks have gone by. In general, make sure you have good tires and you're going slow when the roads aren't great and you get off the roads when they're legit bad or icy. I usually check New England 511 and think "Is it getting better or worse now?" and make my plans accordingly.
posted by jessamyn at 11:32 AM on December 18, 2016 [1 favorite]

The worst ice is when the ground is colder than freezing and you get freezing rain on it. For normal snow pack get some heavily siped tires (a lot of people swear by Nokians) and just keep neutral/light on the controls - don't steer sharply, don't brake heavily and don't try to accelerate too quickly. The most insidious thing about wet ice is that you may not realize you have basically no control until you get to even gentle hill/curve.
posted by 445supermag at 11:48 AM on December 18, 2016 [1 favorite]

I do have winter tires and about 100 lbs of sand in the back of my small 2WD hatchback

The sand might actually do more harm than good, especially if you have a front wheel drive (check these experts).
posted by bluefrog at 4:01 PM on December 18, 2016 [2 favorites]

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