[bobthepanda]

There have been discussions about adding back artificial noise, since a noiseless car would be extremely difficult to detect for people who don't have sight.

Also a fair amount of noise generated by cars is not the engine; for example, you have the sound of the tires rolling on the pavement.

[asutekku]

Most of the time on certain environments you don’t hear the cars motors at all, all you hear are the tires having a contact with the ground.

[crazygringo]

Edit: removing my comment because I was wrong. Turns out tire noise can be louder. Thanks to commenters below for correction!

[wffurr]

Combustion engine is only louder below about 35 mph.

https://en.wikipedia.org/wiki/Roadway_noise

"...rolling tires driving on pavement is found to be the biggest contributor of highway noise which increases with higher vehicle speeds."

[dashundchen]

In the US there are plenty of poorly maintained vehicles on the road emitting a lot of other nosies - squeaky belts, damaged or missing mufflers, rattling panels, worn brake rotors or pads.

Most states have very lax inspection requirements.

Even in my state, which supposedly is one of the strictest on inspections, it's surprisingly easy to have a dangerous failing car pass.

Living near a busy intersection you hear all sorts of weird mechanical failures as cars brake and accelerate from the stoplight.

[wffurr]

While a highway with high speed traffic sounds like a loud whooshing sound, from tires on pavement and air displacement. Engine sounds are almost impossible to notice.

Intersection sounds like <35 mph, so you are agreeing with me.

[petewailes]

Afraid not. Most noise from modern cars is tyre noise at speeds where you're most likely to encounter it.

I have a weird obsession with road noise and how it relates to road surface construction.

[jeffbee]

Isn’t it also the case that a big heavy car with gigantic tires is louder than a lighter car with narrower tires? A Tesla Model X is pretty dang loud at 45 MPH, compared to something like a BMW i3 that weighs half as much and looks like it wears bicycle tires.

[petewailes]

Absolutely. Basically the volume of sound emitted increases in proportion to the tyre size and speed, and also is affected by its tread pattern.

In short, the road noise from tyres is due to air being compressed by the tread and then released again. It's basically a constant rolling version of clapping your hands.

Modern formulations of tarmac are designed to settle with air channels (called voidage) to provide an exhaust for that air, significantly reducing the volume. If you want more information on a couple of types, look up stone-matrix asphalt or open-graded friction course. Concrete on the other hand is notoriously poor for sound reduction, because the surface is so much smoother.

As a rough rule of thumb, quietened surfaces come in at 6-9db lower than a comparable non-quietened surface.

ARFC is another kind, made of recycled rubber mixed as a secondary aggregate. It's commonly used as a quiet and long lasting surface in parts of the US, and has the advantage of being a good product for using up waste tyres. In the UK we have different compounds, which do similar things. The M4 between Swindon and Bristol is a particular treat to drive on acoustically.

Undersurface is potentially an issue too. For example, concrete surfaced in mono-aggregate based tarmac has a tendency to resonate and "sing". Concrete with undulations does the same, though for different reasons.

I could go on for some time but it's kinda dull.

[formerly_proven]

> I could go on for some time but it's kinda dull.

I find civil engineering is often quite interesting, because the tradeoffs and issues can be surprisingly inobvious.

[wizzwizz4]

Do you have a blog? (I checked your bio, but your personal domain seems to redirect to your work now.)

[formerly_proven]

Small naturally aspirated gasoline engines are also quieter than turbodiesels. With some good noise dampening in the engine compartment and exhaust system some cars are surprisingly quiet even at low speeds. Also, some roads are louder than others (cobblestone being very loud regardless of speed).