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.
Have you seen some modeling of carrying capacity for highways at different speeds? You may be right, of course.
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.)
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.
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.
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.
All that said, I don't know what to say about driving 3-4 hours a day. After working 8-10 hours, and driving for 3-4 hours, there's not a lot day left before you have to start all over. Driving a total of 150 miles for groceries blows my mind; that's basically the width of the top half of Louisiana.
Cars today are much more aerodynamic than they were 50 years ago. That almost certainly changes the "economics" of such a change drastically.
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.
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.
Volvo V60, 4 cyl gasoline engine, 2016 model.
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.
2. Electric cars can go MUCH further at slower speeds than at higher speeds. It is something like 25mph that maximizes range, at least with the Model S and Mach E.
3. Speed governors for cars, though probably highly unpopular amongst drivers, would probably save a lot of fuel.
Even without signage, I imagine word of a new national speed limit would travel *pretty* quickly.
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/20...
That said, it will take a very charismatic politician to get anything done in that regard.