We live in a typical Chicago suburb, where attached garages are even with the fronts of most houses, with paved driveways to the street. There is a front sidewalk parallel to the street, which divides the front lawn from the parkway.
This morning the temp is right at freezing, and there is a light dusting of snow on roofs and grass. Most pavement - streets and sidewalks, however, are damp, not snow-covered. The exception is a portion of most driveways where they intersect with sidewalks, which are covered with a dusting of snow. Our brick driveway seems to have a heavier/wider dusting than most others. This is mostly on blocks running N/S, so there don’t seem to be significant shadows in play.
Wondered why this might be. Obviously, those areas are colder than the rest of the sidewalks, but not sure why. Does it have to do with the thickness of the paving to allow cars to drive on it? I assume the streets are wet due to accumulated salt.
Just a kinda odd phenomena we noted as we walked the dog.
WAG: even if they haven’t recently been salted, the streets & sidewalks have been salted in the past. They retain the salt for a long time. Again, just a WAG.
My house is on a curved part of the street and I have noticed that my driveway often has snow whereas some of my neighbors don’t. I’ve come to the conclusion that it is due to the angle from which the driveways are facing the sun. As for sidewalks, they are generally 90 degrees perpendicular to driveways, so perhaps the angle to the sun is a factor here as well.
I like the residual salt explanation. I also wonder in the case of streets if the thickness and composition of asphalt lends itself to a greater capacity to retain heat compared to the relatively thin layer of concrete that most driveways are typically constructed with.
In the case of comparing accumulation specifically on concrete sidewalks to concrete driveways, I must confess I’ve not observed any difference between the two. Given the fact that they’re both constructed with the same materials could only explain any differences by the presence of residual salt.
I suspect there’s a lot greater accumulation of oil, grease and other substances on roads compared to driveways, that contribute to lack of accumulation of snow at near-freezing temperatures.
Yeah, direction of the sun makes a big difference. My south-facing front lawn always melts long before the north-facing front lawns across the street. In looking at it, you wouldn’t imagine there would be much difference, but even a little bit of shade from the house slows down the heating of the yard by quite a bit.
Are the other driveways made of the same material as the sidewalk ? My driveway is made of the same material as the sidewalk and I’ve never seen a difference in snow between the driveway and the sidewalk next to it , but plenty of driveways are not made of the same material as the sidewalk.
The driveways are all different materials: concrete; asphalt; pavers/brick. We noticed this pattern on a types of materials. But it was NOT consistent. I’d estimate 2/3 of the driveways on one block showed this pattern, with maybe 1/3 on the next block.
We walk the dog on these blocks every day. I assure you that the use of salt on residential sidewalks is minimal if not nonexistent. To the contrary, I would expect the driveways (and where driveways cross sidewalks) to have more residual salt from the streets.
The concrete is quite variety in terms of smoothness, aggregate, etc. On one stretch of sidewalk, it apaeared that a rougher stretch of concrete had more accumulation than the adjoining smooth section. Most of the driveways tend towards smooth.
My wife and I play quite a bit of attention to light/shadows/etc. - we are both avid gardeners and she is an amateur astronomer. We were unable to identify any way that the sun’s position could have caused this. We walked shortly after sunrise, and today was quite cloudy.
I remain confused (about this and countless other things!)
Driveways are closer to buildings, and therefore get blanketed from the sun more. On my street, the driveways facing south often are clear while the driveways facing North are still covered in snow. Even if the driveway faces the right way, it will still be in more shadow during the day than will the street.
The snow was not accumulating near the houses on either the east or west sides of the street, Instead, the accumulation was where the driveway crosses the sidewalk - approx 20 from the house. (I believe homes here have a 30 setback from the curb.)
We did not count, but didn’t notice any difference in frequency on East vs West sides of the blocks. Moreover, at this time of year, the sun is awfully low. Shadow effect is clearly evident on the short N ends of blocks, where houses and fences cast shadows and snow melt/evaporation/transpiration is much slower.
BTW - those of you talking about the sun, are you talking about the effect of the sun TODAY, or residual heat from YESTERDAY’S sun? As I said, the sun was not yet up today when we saw this, so it couldn’t have been a factor in the overnight accumulation factor. Yesterday’s temp was a high of 42 and a low of 33. Seems like it has been mostly cloudy and between 32-45 the past few days. This morning I saw readings of 32 and 31 F.
But, as I said, we have lived here 9 years, walk our dog up and down these streets every day, and are very aware that it is extremely rare for any of these property owners to salt their sidewalks.
If anyone salts anywhere, it tends to be right up near their front door. I don’t see any way people applying salt to the public sidewalks explains this pattern. And, if they WERE salting their sidewalk, why would they NOT salt the portion of the sidewalk that crosses their driveway?
What is the likelihood that the water/sewer lines run under the street, creating a de facto, if marginal, hydronic heating system – at least, relative to the driveways?
Water/sewer DOES run under the street - as I believe it does in many/most places. I don’t see how that explains the pattern on the sidewalks. Our town salts the streets pretty heavily, last time (I think) during the x-mas weekend snow.
Individual lines run perpendicularly from the street to each house. Some under driveways, some across lawns. We did not note different melt/accumulation patterns based on the location of the buffalo boxes. Would be shocked if the household lines were warm enough to cause the snow to melt rather than accumulate on so much of the sidewalks. And accumulation was pretty even across the sidewalks - not showing the water/sewer lines.
Spit a little snow this afternoon. Just hauled the trash cans to the curb and the ONLY accumulation is a football shaped ellipse (is that redundant?) covering the portion of the sidewalk crossing my brick driveway, and a foot or 2 of the brick drive/apron on either side.
I gotta imagine it is something about the hard surface on either side keeping that section of the walk cooler than the portions with grass on either side.
Didn’t see much accumulation on the closest drives.
There is the possibility that its due to the road and footpaths generally being bonded down to clay or other high thermal conductive material. its above freezing down below… a heatsink that provides heat to the surface for a while…
Driveways and privately installed pavements may be thin, floating on sand or dry material and on well drained surfaces, slopes… and so not so well connected to the heatsink below…
Its a factor when the air temp is only just below freezing and the snow is thin… It can show the difference the extra heat from below is making.
Of course I meant sublimation rather than transpiration - doh!
And thanks, Isildur - sounds like a definite possibility. I guess I sorta thought driveways would be thicker - more solidly bonded - to support cars. Dammit Jim, I’m a lawyer, not a civil engineer!