How much warming occurs on a road surface due to traffic?

Another topic asking for thoughts – road surfaces are likely to be warmed up by the friction of tires traveling on them.

But how much warming happens?

I seem to recall that after some rain, the “tracks” where tires travel seem to dry faster than the rest of the road surface. So that’s one possible data point.
Another data point might be the similar effect that seems to occur with (light) snow, which seems separate from just physical removal of the snow.

A third data point is that tires warm by about 50 degrees F at highway speeds, which suggests some warming of the road surface where there’s continuous ample traffic (like stretches of some interstates).

Is this another Bar Room discussion like your turning tires while stationary ?

only if you want to drink while joining in or reading… NO bar fight(s) intended

yet I am seriously interested in input / thoughts / leads – kind of like in the spirit of the two brothers bouncing an idea around

(and like the turning tires while stationary, this is about a real world thing that happens every day AND does not have much (if any) info on CarTalk when I searched for it

btw, I did learn some relevant things from the turning tires thread)

You really think anyone is going to spend time and money on a survey like this ?
Too many factors to even reach a marginal figure :thinking:

Road construction ( asphalt or concrete ) - ambient temperature - tire thread of the majority of vehicles - average vehicle weight - vehicle speed - even the ground temperature .

As I said, NO bar room fights intended – I hope you can share that sentiment.

And you should NOT think I’m expecting someone “to spend time and money on a survey like this”

“Too many factors to even reach a marginal figure”
Thanks for your personal view – although I don’t know what “figure” you have in mind.

OTOH, any information is better than no information, and this forum makes possible the benefit of additional observations and experiences by others – I hope you aren’t trying to discourage others from participating (or even starting threads)

“Road construction ( asphalt or concrete )”
yes, observations and experiences welcome

“ambient temperature”
yes, observations and experiences welcome

“tire thread of the majority of vehicles”
yes, observations and experiences welcome – although that probably averages out to be about the same on busy, continuous ample traffic stretches of road

“average vehicle weight”

“vehicle speed”
yes, observations and experiences welcome – although that’s a relatively narrow range on busy, continuous ample traffic stretches of road

“the ground temperature”
yes, observations and experiences welcome – in fact, I left out the observation that in summer months in some places, road surfaces will remain warmer than air temp for some time after dark,
while in winter months in some places, road surfaces will remain cooler than air temp for some time after daybreak

There definitely is heat being generated, but not sure exactly how much.

My thought is the tracks are due to the displacement of water from tires rather than heat


I have run tests on tires operating on an 8’ diameter test wheel and the tires did get noticeably hot as speed increases and inflation pressure decreases as did the test wheel. All tires were run until they failed with the pressure being lowered and the speed increased until the tire separated and at that time tread rubber would be gumming up and smoking on the test wheel.

I gotta believe it is negligible. Just got back off the road from wet from snow and as soon as it cools down a little that wet will be ice, regardless of traffic volumes.

In traffic, the tracks on a wet road will dry faster the same as if you dry your hands on a towel. The tires are picking up the water and spraying it away. Not much to do with heat in my view.

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Good point, although I wonder if there are examples of light snow conditions where other effects are seen – like where a dusting of snow is displaced (or pressure melted) by tire traffic and then the small amount of liquid is heat evaporated rather than displaced.

If I may ask, what surface were in contact with the test tires and did that surface get hot?

Thanks – and it makes me think of the reverse condition: as conditions warm up, do the tire traffic tracks in light snow or a little ice melt faster than the adjacent areas not in the tracks?
Your condition probably happens a lot in some places as the sun sets and temperatures cool while the reverse happens after sun rise and as temperatures increase.

Yes of course, where salt has been applied, the tracks are usually the first to melt leaving snow or ice in the center and sides for a while. I don’t think it’s got much to do with tire heat though.

The test station looked similar to this

and the contact surface was similar in texture to crocus cloth but with years of use there was a heavy coat of rubber at the center.

So here’s a whitepaper I found that contains information related to heat conduction to the road surface. Granted it is related to race tires but it outlines the major paths and their relative contribution:

The majority of a race tire’s heat is lost at the tire-road and tire-air (external)
interfaces. Assuming the tire is hotter than the ambient, heat is lost at the
tire-road interface from conduction into the ground, and at the tire-air
interface from forced convection with the ambient air. Heat losses from
radiation are only significant for temperatures > 100˚C and are often ignored.
However, heat to and from the tire can also be managed at the wheel-tire
interface; brakes feed temperature into the wheels & tires but wheels can
also be used to cool & thermally manage the tire.
Given the significant heat losses at the tire-road interface and transient heat
generation at the surface (surface heat generation is highly dependent on slip
ratio, slip angle, and load), a race tire’s surface temperature fluctuates rapidly
with dynamic loading.

Here’s another source of info:

Wow! Thanks very much!

[edit: interesting that tires with less tread (and/or less load) apparently generate less heat, and so would have less heat to transfer to the road surface or to the air ]

Thanks for that!

I always hate saying, "don’t know, don’t care, but…"

Running through the changes going through the stages
Coming round the corners in my life
Leaving doubt to fate staying out too late
Waiting for the moon to say goodniiiigh-hi-hi-hite
And I could cry for the time I’ve wasted
But that’s a waste of time and tears
And I know just what I’d change
If I went back in time somehow
But there’s nothing I can do about it now

Lyrics by Beth Nielsen Chapman, performed………… by Willie Nelson
:palm_tree: :sunglasses: :palm_tree:

My experience with light snow is the tires compact the snow into ice. Light snow is sometimes worse than a heavier snow.

Light snow means colder temps…so it can quickly turn to ice and make for slick driving conditions. When my middle child was new to driving…one morning it snowed about 1/2" and the temps were below 20. I told my son as he drove off to school to be careful because the roads were going to be slick. Luckily he heeded my warning. Said he saw many cars off the road and a 5 car crash on the way to school.

Better explained by the fact that tires are designed to fling the water out to the sides and therefore out of the “tracks.”

The tire does briefly heat the road under it, which is why you slide on ice. The tire melts the top layer of ice, and that water makes it easy to slide around on ice. The same mechanism is what causes you to slip while walking on ice. When it’s extremely cold, ice actually isn’t very slippery when you walk on it because the pressure of your weight can’t melt it before you’ve taken your next step.

The heating is more from compression due to the weight than from the tire being warm. Any time you change something’s shape, you end up with heat as a byproduct (which is why it’s always so funny in movies when they want to show someone is strong, so they have him bend a steel bar. Thing would be red hot if you bent it that fast). You’re pressing down on the road with a 3,000 pound plus vehicle - that’s gonna heat it up too. But unless you’re driving something like NASA’s crawler transporter, the heating isn’t going to be all that significant, especially since you’re probably moving over any given section of road at a pretty good clip.