5 ms·

We could cut speed limits from 70-75 to 50 (assuming most people do "five over") like we did in the seventies. This reduces fuel consumption by about 40%, assum

We could cut speed limits from 70-75 to 50 (assuming most people do "five over") like we did in the seventies. This reduces fuel consumption by about 40%, assuming fuel consumption is proportional to the cross-sectional area of a vehicle and the square of its velocity. This isn't a silver bullet, but 40% is nothing to sneeze at.

airstrike 5y ago
This would never work for political / social reasons.
- cjohnson318 5y ago
  It worked in the seventies during the oil embargo.
  - airstrike 5y ago
    Electric cars didn't exist then.
    - cjohnson318 5y ago
      You're right, electric cars were not available in the 1970's. However, unless you're generating and storing enough solar power to power your car year round, at anywhere from 2-17kWh a day, then your electric vehicle will still be using fossil fuels. Even power grids that utilize solar farms still need natural gas plants online that can handle shortages on short notice.
- meristohm 5y ago
  What will it take to shift culture so that these solutions are adopted?
  - JohnWhigham 5y ago
    Better alternatives to driving yourself on the highway. Penalizing consumer behavior on a micro level rarely works out well (it's the same discussion with something like a meat tax; it just pisses people off).
    - zip1234 5y ago
      Unfortunately, driving is currently massively subsidized. If drivers simply had to pay for the road usage and the negative externalities of driving, such as noise and pollution, I think a lot less people would drive. Gas taxes and fees currently cover less than half of road spending alone, not even paying anything for pollution, noise, or other externalities. That said, it will take a very charismatic politician to get anything done in that regard.
      - closeparen 5y ago
        If transit advocates had to pay for the time people would spend waiting for the bus and for the rent premium associated with transit access under their proposed policies, I think a lot fewer people would repeat this line.
asciident 5y ago
It's an interesting idea. Wouldn't the cost of raising funds, replacing all the signs, etc. be also damaging? What about having a clear "no speeding at all on speeds over 50mph" announcement, and start a campaign to enforce speeding even at 0.1mph over? That would quickly normalize driving at 10-15 miles under.
- cjohnson318 5y ago
  I don't think replacing signs would be large line item compared to our foreign wars budget, at any rate, all of that money would flow back into the economy pretty quickly as those workers spent their paychecks. Even without signage, I imagine word of a new national speed limit would travel *pretty* quickly.
lostapathy 5y ago
Would this still have the same impact it did in the 70's? Cars today are much more aerodynamic than they were 50 years ago. That almost certainly changes the "economics" of such a change drastically.
- cjohnson318 5y ago
  Yes, I think so. Cars in the seventies also tended to be smaller, meaning there was a smaller cross-sectional area on the vehicle. I think we have more efficient engines now, but I think the differences between larger more aerodynamic vehicles versus smaller less aerodynamic vehicles is negligible. If someone has numbers, then I'm happy to change my mind.
imoverclocked 5y ago
I think cars are configured to be more efficient at higher than 50 mph these days.
- cjohnson318 5y ago
  I think the optimal speed for fuel efficiency for most vehicles is around 55 mph, give or take a 2-3 miles per hour. Edit: I was mistaken, this is from the Guardian: > The Energy Saving Trust says that the most efficient speed you can travel in a car in terms of achieving the best fuel economy is 55-65mph. Any faster, though, and the fuel efficiency decreases rapidly. For example, driving at 85mph uses 40% more fuel than at 70mph (oh, and it's illegal too). https://www.theguardian.com/environment/green-living-blog/2011/mar/25/hypermiling-tips https://www.theguardian.com/environment/green-living-blog/20...
titzer 5y ago
My car has a realtime mpg output. I can manage 35mpg at 75mph on cruise control. I do not get 40% better economy at 55mph. You know what kills fuel economy? Not being on cruise control. After 3000+ highway miles this month, I can definitely say that drivers loitering in the passing lane (there's a reason why they have KEEP RIGHT EXCEPT TO PASS signs) cost enormous amounts of fuel due to the congestion and consequent and avoidable acceleration/deccelaration.
- cjohnson318 5y ago
  That's very interesting. What kind of car do you drive? Do you know what your fuel efficiency is at 55mph? I would certainly expect there to be some difference between 75mph and 55mph.
  - titzer 5y ago
    There is a difference, but it is not 40%. I am usually not in the habit of setting cruise for 55mph on the highway, but I suppose I can try :) Volvo V60, 4 cyl gasoline engine, 2016 model.
    - cjohnson318 5y ago
      For most vehicles, you see fuel efficiency start to take a hit around 55mph. The thing is that the velocity term in the air resistance equation is squared, so at some point your fuel efficiency starts dropping very, very quickly.
  - jcims 5y ago
    I ran into a similar issue with a 2003 Honda Accord (v6 manual trans, one of my favorite cars ever). I was spending almost 4 hours a day in the car for a three month job and went through all sorts of experiments to find peak efficiency. If I was on a level section of road, I could get better mileage by driving slower, e.g. 55 vs 75. But when I started to negotiate hills and have to accelerate to maintain speed, the mileage dropped way down because the engine wasn't efficient at generating power at those lower RPMs. And this is where you start to see these unexpected patterns in mileage with gas/diesel engines...they have a very lumpy efficiency curve, and it's regularly more important to stay in a specific RPM range than a specific speed if you want to maximize mileage. Once you start going up to 80-90-100mph physics takes over, of course, but there is a lot of variability in between. At the time I was just thinking fuel prices and it got to the point where I was calculating how much I was saving by driving slower and it was cents per hour. I ultimately landed on 70mph as the sweet spot, and I would regularly get 32mpg.
twobitshifter 5y ago
It’s a good idea. We could also incentivize companies to allow work from home to keep cars off the road. It’s discouraging how companies are ignoring the environmental footprint of going back to the office - but maybe if the government rewarded wfh they’ll change.
jcims 5y ago
One thing to keep in mind is that this decreases the carrying capacity of highways (cars spending more time in a lane of traffic) and could result in more construction.
- meristohm 5y ago
  Fine. Maybe we don’t get to drive so much. What’s a reasonable per-person carbon and water quota? (with need-based exceptions, since giving up compassion and care for the differently-abled people is way low on my priority list) Imposing regulations that limits energy and transportation feels appropriate. Prioritize survival (and housing, education, and healthcare, and helping people come to terms with mortality), and help retrain people to do more with less. Laying under a tree yesterday in 37C (not as hot as Portland that day, or as humid as what I remember from the Midwest or South) I enjoyed the high-def, ultra-wide view above (birds, insects, leaves, sky) and below (ants, other insects, spiders, plants, soil). The olfactory emitter is top-notch, too, and the sound quality can’t be beat.
- OldHand2018 5y ago
  As you travel faster, you must increase the distance between cars for safety - decreasing the number of cars that can fit within a certain length of highway. But… Have you seen some modeling of carrying capacity for highways at different speeds? You may be right, of course.
- zip1234 5y ago
  It 'may' decrease carrying capacity of highways. Also, induced demand is a real observed phenomenon with roadways. The more capacity there is, the more people will drive. Paradoxically, when capacity is removed, traffic will often just dry up. Highway agencies know this but still use traffic models to justify expansion that are self-fulfilling projections.
  - jcims 5y ago
    This seems like an awfully simplistic first order analysis that doesn't consider the end to end economics of driving. Location is an economic constraint, and the ability to reduce or eliminate that constraint at will is very powerful. The fact that (some) traffic fills to capacity on a specific road just means there is economic demand surplus for travel between points connected by that particular route at that particular time. This demand tapers off when the roadway reaches capacity because another cost begins to grow exponentially. Travel in congested traffic quite literally causes people to murder each other. This cost, the stress of driving on congested roadways, doesn't seem to surface much because it's difficult to quantify. However, for me, it is the one thing that will cause me to change my plans. (edit: It's easy to distill 'economic' motivation into profit. That's not my intent here. My view is that there is no intrinsic value of anything, the sun could have exploded 7 minutes ago and if anyone outside of its reach is there to witness it they might catalogue it as ES0481A (in 4+ years). I use 'economic' as an encapsulation of human desire to live and to thrive and its important to me and to this argument from that perspective.)
jandrewrogers 5y ago
There are large regions of the US where the posted limit is 80, and the real limit is even higher. Reducing the speed to 50 would literally add an hour or more to daily commutes in some of these regions. It isn't the person in the city that is making a sacrifice by reducing speed limits. An obvious flaw with this idea is that enforcement is local and discretionary. There are many jurisdictions that refuse to enforce posted speed limits today, never mind a limit of 50 which would be extremely unpopular.
- cjohnson318 5y ago
  Some states have 80mph stretches, but it's not the norm. Also, I think inner-city driving is a lot more time consuming than the long, high speed stretches between urban centers. If you only consider reducing speed on highways, then you have to cover very large differences before you encounter an additional hour off round-trip commute time. At 50mph, you'd need to drive about 90 miles to add an hour to your total round trip, compared to driving 70mph. At 55mph, you'd need to drive about 130 miles, to add an hour to your total round trip, compared to driving 70mph. Unfortunately, driving in cities is inelastic when it comes to fuel efficiency unless you hop on a bus. For highway driving, 55mph is annoying, but it's not unbearable, and you're making a real and measurable difference. For reference, 55mph is the standard in California for vehicles with more than two axles.
  - jandrewrogers 5y ago
    In the mountain west 80mph is the norm, and even then it is more of a suggestion, flow of traffic is closer to 90mph. Some states are posted 70mph on single-lane county roads. Many practical logistics of living in those regions become infeasible at 50mph because people have schedules and finite amounts of time for travel. You are being unrealistic about the implications. When you live in the parts of the country that have 80mph limits, and I have, it is normal to spend 3-4 hours driving in a day. Things are very spread out and the distances are far, which is why the speed limits are so high. I've lived in towns where basic things like shopping were a 75 mile drive each way. Casually increasing those drive times by 75% is not a small thing and, frankly, no one would comply. You'll end up in exactly the situation you already have -- people in urban areas will drive slowly and people in more sparsely populated regions will drive as fast as is reasonably safe. The fact that these higher limits are largely in remote areas also has the implication that not that many people are driving that fast anyway, so it is unlikely to have much impact anyway. It would rightly generate considerable resentment with no meaningful impact on carbon emissions. All that aside, my car hits peak efficiency at around 70mph, as did my prior car. You can monitor this in many cars and I do. Drivetrains are optimized for typical highway speeds. It isn't the 1970s.

airstrike 5y ago

This would never work for political / social reasons.

cjohnson318 5y ago
It worked in the seventies during the oil embargo.
- airstrike 5y ago
  Electric cars didn't exist then.
  - cjohnson318 5y ago
    You're right, electric cars were not available in the 1970's. However, unless you're generating and storing enough solar power to power your car year round, at anywhere from 2-17kWh a day, then your electric vehicle will still be using fossil fuels. Even power grids that utilize solar farms still need natural gas plants online that can handle shortages on short notice.
meristohm 5y ago
What will it take to shift culture so that these solutions are adopted?
- JohnWhigham 5y ago
  Better alternatives to driving yourself on the highway. Penalizing consumer behavior on a micro level rarely works out well (it's the same discussion with something like a meat tax; it just pisses people off).
  - zip1234 5y ago
    Unfortunately, driving is currently massively subsidized. If drivers simply had to pay for the road usage and the negative externalities of driving, such as noise and pollution, I think a lot less people would drive. Gas taxes and fees currently cover less than half of road spending alone, not even paying anything for pollution, noise, or other externalities. That said, it will take a very charismatic politician to get anything done in that regard.
    - closeparen 5y ago
      If transit advocates had to pay for the time people would spend waiting for the bus and for the rent premium associated with transit access under their proposed policies, I think a lot fewer people would repeat this line.

asciident 5y ago

It's an interesting idea. Wouldn't the cost of raising funds, replacing all the signs, etc. be also damaging? What about having a clear "no speeding at all on speeds over 50mph" announcement, and start a campaign to enforce speeding even at 0.1mph over? That would quickly normalize driving at 10-15 miles under.

cjohnson318 5y ago
I don't think replacing signs would be large line item compared to our foreign wars budget, at any rate, all of that money would flow back into the economy pretty quickly as those workers spent their paychecks. Even without signage, I imagine word of a new national speed limit would travel *pretty* quickly.

lostapathy 5y ago

Would this still have the same impact it did in the 70's? Cars today are much more aerodynamic than they were 50 years ago. That almost certainly changes the "economics" of such a change drastically.

cjohnson318 5y ago
Yes, I think so. Cars in the seventies also tended to be smaller, meaning there was a smaller cross-sectional area on the vehicle. I think we have more efficient engines now, but I think the differences between larger more aerodynamic vehicles versus smaller less aerodynamic vehicles is negligible. If someone has numbers, then I'm happy to change my mind.

imoverclocked 5y ago

I think cars are configured to be more efficient at higher than 50 mph these days.

cjohnson318 5y ago
I think the optimal speed for fuel efficiency for most vehicles is around 55 mph, give or take a 2-3 miles per hour. Edit: I was mistaken, this is from the Guardian: > The Energy Saving Trust says that the most efficient speed you can travel in a car in terms of achieving the best fuel economy is 55-65mph. Any faster, though, and the fuel efficiency decreases rapidly. For example, driving at 85mph uses 40% more fuel than at 70mph (oh, and it's illegal too). https://www.theguardian.com/environment/green-living-blog/2011/mar/25/hypermiling-tips https://www.theguardian.com/environment/green-living-blog/20...

titzer 5y ago

My car has a realtime mpg output. I can manage 35mpg at 75mph on cruise control. I do not get 40% better economy at 55mph. You know what kills fuel economy? Not being on cruise control. After 3000+ highway miles this month, I can definitely say that drivers loitering in the passing lane (there's a reason why they have KEEP RIGHT EXCEPT TO PASS signs) cost enormous amounts of fuel due to the congestion and consequent and avoidable acceleration/deccelaration.

cjohnson318 5y ago
That's very interesting. What kind of car do you drive? Do you know what your fuel efficiency is at 55mph? I would certainly expect there to be some difference between 75mph and 55mph.
- titzer 5y ago
  There is a difference, but it is not 40%. I am usually not in the habit of setting cruise for 55mph on the highway, but I suppose I can try :) Volvo V60, 4 cyl gasoline engine, 2016 model.
  - cjohnson318 5y ago
    For most vehicles, you see fuel efficiency start to take a hit around 55mph. The thing is that the velocity term in the air resistance equation is squared, so at some point your fuel efficiency starts dropping very, very quickly.
- jcims 5y ago
  I ran into a similar issue with a 2003 Honda Accord (v6 manual trans, one of my favorite cars ever). I was spending almost 4 hours a day in the car for a three month job and went through all sorts of experiments to find peak efficiency. If I was on a level section of road, I could get better mileage by driving slower, e.g. 55 vs 75. But when I started to negotiate hills and have to accelerate to maintain speed, the mileage dropped way down because the engine wasn't efficient at generating power at those lower RPMs. And this is where you start to see these unexpected patterns in mileage with gas/diesel engines...they have a very lumpy efficiency curve, and it's regularly more important to stay in a specific RPM range than a specific speed if you want to maximize mileage. Once you start going up to 80-90-100mph physics takes over, of course, but there is a lot of variability in between. At the time I was just thinking fuel prices and it got to the point where I was calculating how much I was saving by driving slower and it was cents per hour. I ultimately landed on 70mph as the sweet spot, and I would regularly get 32mpg.

twobitshifter 5y ago

It’s a good idea. We could also incentivize companies to allow work from home to keep cars off the road. It’s discouraging how companies are ignoring the environmental footprint of going back to the office - but maybe if the government rewarded wfh they’ll change.

jcims 5y ago

One thing to keep in mind is that this decreases the carrying capacity of highways (cars spending more time in a lane of traffic) and could result in more construction.

meristohm 5y ago
Fine. Maybe we don’t get to drive so much. What’s a reasonable per-person carbon and water quota? (with need-based exceptions, since giving up compassion and care for the differently-abled people is way low on my priority list) Imposing regulations that limits energy and transportation feels appropriate. Prioritize survival (and housing, education, and healthcare, and helping people come to terms with mortality), and help retrain people to do more with less. Laying under a tree yesterday in 37C (not as hot as Portland that day, or as humid as what I remember from the Midwest or South) I enjoyed the high-def, ultra-wide view above (birds, insects, leaves, sky) and below (ants, other insects, spiders, plants, soil). The olfactory emitter is top-notch, too, and the sound quality can’t be beat.
OldHand2018 5y ago
As you travel faster, you must increase the distance between cars for safety - decreasing the number of cars that can fit within a certain length of highway. But… Have you seen some modeling of carrying capacity for highways at different speeds? You may be right, of course.
zip1234 5y ago
It 'may' decrease carrying capacity of highways. Also, induced demand is a real observed phenomenon with roadways. The more capacity there is, the more people will drive. Paradoxically, when capacity is removed, traffic will often just dry up. Highway agencies know this but still use traffic models to justify expansion that are self-fulfilling projections.
- jcims 5y ago
  This seems like an awfully simplistic first order analysis that doesn't consider the end to end economics of driving. Location is an economic constraint, and the ability to reduce or eliminate that constraint at will is very powerful. The fact that (some) traffic fills to capacity on a specific road just means there is economic demand surplus for travel between points connected by that particular route at that particular time. This demand tapers off when the roadway reaches capacity because another cost begins to grow exponentially. Travel in congested traffic quite literally causes people to murder each other. This cost, the stress of driving on congested roadways, doesn't seem to surface much because it's difficult to quantify. However, for me, it is the one thing that will cause me to change my plans. (edit: It's easy to distill 'economic' motivation into profit. That's not my intent here. My view is that there is no intrinsic value of anything, the sun could have exploded 7 minutes ago and if anyone outside of its reach is there to witness it they might catalogue it as ES0481A (in 4+ years). I use 'economic' as an encapsulation of human desire to live and to thrive and its important to me and to this argument from that perspective.)

jandrewrogers 5y ago

There are large regions of the US where the posted limit is 80, and the real limit is even higher. Reducing the speed to 50 would literally add an hour or more to daily commutes in some of these regions. It isn't the person in the city that is making a sacrifice by reducing speed limits. An obvious flaw with this idea is that enforcement is local and discretionary. There are many jurisdictions that refuse to enforce posted speed limits today, never mind a limit of 50 which would be extremely unpopular.

cjohnson318 5y ago
Some states have 80mph stretches, but it's not the norm. Also, I think inner-city driving is a lot more time consuming than the long, high speed stretches between urban centers. If you only consider reducing speed on highways, then you have to cover very large differences before you encounter an additional hour off round-trip commute time. At 50mph, you'd need to drive about 90 miles to add an hour to your total round trip, compared to driving 70mph. At 55mph, you'd need to drive about 130 miles, to add an hour to your total round trip, compared to driving 70mph. Unfortunately, driving in cities is inelastic when it comes to fuel efficiency unless you hop on a bus. For highway driving, 55mph is annoying, but it's not unbearable, and you're making a real and measurable difference. For reference, 55mph is the standard in California for vehicles with more than two axles.
- jandrewrogers 5y ago
  In the mountain west 80mph is the norm, and even then it is more of a suggestion, flow of traffic is closer to 90mph. Some states are posted 70mph on single-lane county roads. Many practical logistics of living in those regions become infeasible at 50mph because people have schedules and finite amounts of time for travel. You are being unrealistic about the implications. When you live in the parts of the country that have 80mph limits, and I have, it is normal to spend 3-4 hours driving in a day. Things are very spread out and the distances are far, which is why the speed limits are so high. I've lived in towns where basic things like shopping were a 75 mile drive each way. Casually increasing those drive times by 75% is not a small thing and, frankly, no one would comply. You'll end up in exactly the situation you already have -- people in urban areas will drive slowly and people in more sparsely populated regions will drive as fast as is reasonably safe. The fact that these higher limits are largely in remote areas also has the implication that not that many people are driving that fast anyway, so it is unlikely to have much impact anyway. It would rightly generate considerable resentment with no meaningful impact on carbon emissions. All that aside, my car hits peak efficiency at around 70mph, as did my prior car. You can monitor this in many cars and I do. Drivetrains are optimized for typical highway speeds. It isn't the 1970s.