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From time to time, the speed limit is reduced due to pollution in France (example (mirror)). Do these reductions apply to electric cars?

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(image source (mirror): MAXPPP)

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I'm french and as far as I know, this is for all types of vehicles. The reduction of pollutant emissions is due to lower car consumption and a slow-moving traffic flow that avoids too much acceleration and braking (study). So I don't see why electric cars should be allowed to drive faster.

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    @Rg7xgW6acQ3g:I am not saying that electric cars pollute as much as other cars. I am simply saying that if electric cars travel faster than others, they can lead to unwanted acceleration and braking and therefore to a loss of traffic flow and an increase in the risk of accidents. No one is above the law, not even the teslas's drivers . – Noé Barras Feb 22 at 9:12
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    Also, all cars (ICE or electric) generate pollution from tire and brake particles, so having the same speed for all traffic (=smaller, less frequent speed changes needed) lowers pollution in all cars. – molnarm Feb 22 at 9:47
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    @molnarm Any reference for the claim that "tire and brake particles" are a non-negligible part of pollution (particulate matter I assume)? Never heard of that and this seems extremely far-fetched, but I might just have missed it. – Voo Feb 22 at 9:51
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    @Voo sciencenews.org/article/… – molnarm Feb 22 at 10:01
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    @Rg7xgW6acQ3g Electric cars exempt from the limit would be prime nucleators of traffic waves, thereby directly contributing to the inefficiency of other traffic. – J... Feb 22 at 12:30
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Here's the thing. Slowing down traffic can actually make it run smoother.

If people expect to go the higher speed, then any bit of open road is considered "lucky" and driving amounts to seizing any bit of luck to sprint to the next bit of congestion. This exacerbates the points of congestion. However if cars respond to open space by cruising at a somewhat reduced speed, the congestion ahead is more likely to clear. The WSJ article talks about a "sweet spot" at 45 mph/72 kph, density that clogs at 65 mph/105 kph will instead run smooth at 45/72.

As far smog (HC/CO/NOx), smooth-cruising engines are much, much cleaner-running than engines doing a lot of "transient events" between different power levels and road speeds. It's very difficult for engine computers to manage transients because it has to play "catch-up" to what the driver is doing. (To hit the optional California NZLEV standards, automakers must remove the "catch-up" factor, with fly-by-wire accelerator pedals and computer-controlled transmission shifting. The computer inserts a small delay so it can now "anticipate" the transient and manage through it). Manual transmissions are much worse for transients (because the NZLEV trick is not possible) and manuals are very popular in Europe.

As far as carbon (CO2/climate change gases), in this case that is not the primary concern, but CO2 emissions are proportional to fuel economy. Brakes are the worst enemy of fuel economy, steady cruise is better, and there's also an aerodynamic factor, with a sweet spot (coincidentally) about 70 kph or 45 mph. This paragraph applies to EVs as far as "fuel" economy, but the CO2 is emitted at the plant smokestack (in France, only true if they charge at peak, because France's base and shoulder generating capacity is nuclear).

So there is very good science behind "slow for smog".

Anyway, allowing EVs to cruise faster would throw a grenade into that first part, the one where denser traffic runs smoother if its "desire" speed is reduced. The EVs bolting in and out would cause congestion, which would make fuel cars make more smog.

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    As far as France is concerned, the speeds in mph feels a little too exotic. Standard international units please :-) ! – JB. With Monica. Feb 22 at 12:57
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    Not sure I understand your third paragraph, but traditional automatic transmissions will normally be much less efficient than manuals traveling steadily at low speeds like 20 KM/H as it's too slow to lock the torque converter. – James Feb 22 at 14:05
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    @JB. MPH is not exotic, it's a backwards relic of an older time when few of us were alive and needs to die a quick death. But as for the numbers in the post, let's say 70 and 110 km/h respectively. They're approximate anyway. – Michael Hampton Feb 23 at 5:00
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    @James: Well, it's a speed reduction by 20 km/h, not to 20 km/h. – O. R. Mapper Feb 23 at 15:59
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    travel.meta.stackexchange.com/questions/585/metric-and-imperial → please kindly edit the units in this answer – miroxlav Feb 23 at 16:59
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Yes, the speed limit applies to all cars.

The information can be found here: https://www.service-public.fr/particuliers/vosdroits/F10332. It's in French obviously. Here is a translation of the relevant parts:

What measures can be taken?

The prefect defines the concerned areas and may decide in particular on the following measures:

  • Moderation of the recommended circulation
  • Reduction of maximum authorized speeds
  • Driving restrictions based on air quality certificates

These measures apply progressively according to the evolution of the pollution peak.

In case of restrictions based on air quality certificates, the prefect specifies the categories of vehicles prohibited from circulation and possible derogations. In any case, vehicles without an air quality certificate or whose air quality certificate corresponds to the most polluting categories are prohibited from driving.

[...]

Where to get information?

Road signs inform you if it has been decided to reduce the maximum authorized speeds or to divert traffic.

For the other restrictive measures, information is obligatorily communicated in the media the day before, before 7pm.

So if you can prove with an air quality certificate that your car is not polluting, it will not be concerned by the last category of driving restrictions. However, the other measures, including modification of speed limit, apply to all cars unless explicitly stated otherwise.

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These restrictions are local and don't always apply to all roads. Typically, the speed limit is reduced by 20 km/h on expressways. Which restriction over which period and which area might vary, you'll want to check the news for more information. That being said, I never heard electric vehicles being singled out of speed restrictions.

In the absence of decisive proof, there are only two things you can do. The first is application of Occam's razor, making no assumptions, so unless noted otherwise the restriction applies to all vehicles everywhere. The second thing is, regardless of what the law allows, drive safely. Electric cars are a minority. Driving 20 km/h faster than all other vehicles, especially in dense traffic, is an accident waiting to happen.

You risk nothing by driving slower like everybody else.

  • This is presuming that the other drivers are actually following the speed limit :) – JonathanReez Supports Monica Feb 22 at 10:39
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    @JonathanReez I'll admit, this is quite the assumption. – AmiralPatate Feb 22 at 10:47
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    @JonathanReez I think it's normal (and expected) to follow the speed limit in France (unlike e.g. Ontario where almost everyone on the highway drives at like 10 kph above the nominal speed limit). – ChrisW Feb 22 at 11:12
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    @ChrisW Rule #1 of driving in France: it is perfectly acceptable to make vehicle-to-vehicle contact with any other road user, moving or stationary, but under NO circumstances EVER make eye-to-eye-contact with the driver ;) – alephzero Feb 22 at 12:13
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    "Driving 20 km/h faster than all other vehicles, especially in dense traffic, is an accident waiting to happen.". How is driving 20 km/h faster than other traffic on a motorway an accident waiting to happen? On motorways vehicles are often overtaken by traffic going faster than them by more than 20 km/h yet accidents are rare. Also, filtering on a motorcycle is usually done in dense traffic and is considered to be safe as long as the difference in speed is reasonable (most will likely say 20/ 30 km/h) – tomsky Feb 22 at 15:18

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