Once you remove the inconsistent skill level, distractedness, irrationality, and emotional reactions that accompany human drivers, you can increase road utilization considerably without a noticeable increase in congestion.
I know a few traffic engineers and one of the things they regularly laugh about are zipper merge advocates (as well as traffic circle advocates, but that's a discussion for another time). It's not that they don't recommend the zipper merge, it's that the advocates think they are magical and ascribe magical effects to them that don't exist in reality.
Want an example of the perfect zipper merge? Look at an hourglass. Thousands of tiny grains of sand perfectly zipper merging at the last instant. And yet there is still a traffic jam. Inflows and outflows still dominate traffic congestion. Now imagine what would happen if you early merged those grains of sand. Your hourglass is now 6 miles tall. Interestingly enough, the early merge is more efficient for flow, but not by enough of a margin (1-2%) to overcome the drawback of the terrible space efficiency.
What the zipper merge is really good at isn't improving flow, it is improving space efficiency. The bottleneck uses far less of the highway when people merge last instant. This allows people to reroute or exit the highway before the traffic jam, reducing the burden on the bottleneck. That's it, nothing more. The idea that traffic would suddenly get so much better if people zipper merged perfectly is not rooted in reality...traffic volume is still the more important factor by several fold.
> This allows people to reroute or exit the highway before the traffic jam, reducing the burden on the bottleneck.
Many of those people could have already been intending to exit the highway earlier. Because of the back-up, their journeys are slowed way down unnecessarily. And then you get compounded effects - the highway backs up past another entrance, causing that feeder road to back up past an intersection... In the worst case you end up with gridlock.
I'm not arguing that zipper merges are magical either, but they can definitely have a significant impact.
Instead, most zoom up until the choke point, then late merge, and rarely do it right, leading to someone slamming their brakes - then traffic jam ensues.
I don't wait for the choke point if I can avoid it. When I see signs that say "construction ahead" or whatnot, I start looking for the signs that say how far ahead, and what lanes. If those don't exist, I try to see what the traffic is doing as far ahead as I can see - looking taillights, turn signals, and anything else - to tell me what lanes are closed, etc.
Then I get over as far and as quick as needed, so I am in the lane I need to be in long before the choke point.
I do the same thing in regular driving; if I know something is going to be on the left side of the street, I try to get over to that side long before I need to - instead of waiting until the last minute and cutting people off (or "begging" with signals to be let in).
I've always found it to be a pain to do it otherwise, even when I don't have the choice and I am forced to, because I have to change speeds and lanes, and that puts me more at risk of collision (it's not the speed that causes problems, but the delta in speeds and lane changes). I'd rather "merge early" (whether that means before real choke point, or just being on the right side of the road to where I am going or turning long before I need to be there) because it seems safer.
The problem is (mainly with choke points, or even on/off ramps) that other people now see the "empty" lane as "I can speed up and go around everyone" and then they get to the choke point and force their way in, or slam on their brakes and swerve, or cause an accident, or anything else. They could see that lane was empty, they had (usually) warning signs miles back saying that the left lanes were closed ahead - but apparently that didn't apply to them.
> reducing the burden on the bottleneck. That's it, nothing more.
That's precisely it though. By reducing the burden of the bottleneck on the greater traffic network, it localizes the congestion to a smaller area and reduces the disruption the rest of the traffic network has to feel. Overall improving congestion, even if locally the congestion still occurs.
> What the zipper merge is really good at isn't improving flow, it is improving space efficiency.
This is based on the human execution of a zipper merge. Ideally, the continuing lane of traffic will be going at a consistent speed with enough space between vehicles to allow the merging traffic to merge without causing a disruption in the flow of traffic. Theoretically you'd get this benefit from merging earlier as well, but as you mentioned the space efficiency causes cascading impacts to other aspects of the traffic network.
That being said, I only mentioned that as a recognizable example. However, a lot of congestion isn't due to a specific trigger such as a lane ending. It's due to bad human driving habits, and suboptimal human reactions to that behavior. Which create phantom traffic jams[1][2]. Self-driving cars will drive more consistently than human drivers, introducing a level of calm in a sea of inconsistent human reactions. Effectively buffering traffic in a way that will improve overall traffic flow, even before we have majority adoption of self-driving cars.
It is possible the reduced need for downtown parking could significantly reduce congestion in cities though.
Self-driving cars will not only be better drivers on the whole, but also allow human drivers to break through inhibitions related to "proper road etiquette", since it's a whole lot easier to do something subjectively rude to a machine than a human.
[1] http://transportation.ky.gov/zippermerge/Pages/default.aspx
[2] https://arstechnica.com/cars/2014/07/the-beauty-of-zipper-me...
[3] https://www.nytimes.com/2016/10/13/us/why-last-second-lane-m...
[4] http://jalopnik.com/stop-trying-to-make-the-zipper-merge-hap...
You're completely right that it could cause an increase in aggressive driving behavior. But it's just as possible that it'll decrease aggressive driving behavior. My conjecture's based off of three personal observations:
1) A lot of the aggressive drivers I know that have road rage-like tendencies take it as a personal affront when another driver does something like turn in front of them or using a less congested lane of traffic to get as far ahead as possible before getting over.
2) One of the most effective strategies I had available as a retail manager to diffuse a situation with an irrational/irate customer was to pass blame on to "the system/corporate policy" if they couldn't see reason. They'd still be irate, but they'd redirect their behavior towards something other than the immediate situation. The same principle applies when you go from blaming a specific driver to blaming "those damn autonomous Nissans. They always <insert some peculiar trait of Nissan's self driving implementation>".
3) Aggressive driving is hard to escalate into full-blown road rage when one participant is a computer. As you said, it'll react to the situation by potentially braking aggressively, but it won't then try to tailgate the individual and escalate the situation. It'll back off appropriately and assure that it's not put into that position again and be done with it. Aggressive drivers will get bored with antagonizing autonomous cars when they get used to them and to the fact that you can't get a rise out of them. As well, autonomous cars can likely get better at identifying indicators/patterns of an aggressive driver and account for that.
Public infrastructure should not be a la carte.
Try that in Phoenix, AZ in the middle of July @ 3pm - I'll even buy you a 2L Camelpak filled with ice water.
Trust me, about an hour in you'll be begging for a car.
Snark aside, the problem in the United States (especially in the southwest) is that our cities aren't set up for walking, nor do we have anywhere near adequate public transportation.
That can't be changed overnight (heck, the Phoenix Metro area has only had light rail system for less than a decade); cities won't become magically walkable or bikeable (and I can't imagine Phoenix ever being this way in the summer, unless every employer installs showers for employee use).
There's also the factor that many people (though the demographics seem to be shifting) see vehicles as more than a tool; they seem them as objects of self-expression - almost like a mechanical costume, in a way. There's also the fact that car affords you the ability to get to your destination on your own schedule, not someone else's. Plus, there's just the sheer joy of driving for driving's sake (sometimes, I like to drive my car just to drive it - no particular destination or reason, just because I like to drive - fancy that).
They are still subsidized (at least in the US). Almost all public transit in the US isn't self-sustaining based on its fares.
The road tax in gasoline is similar. Additionally, most of the wear on roads comes from tractor trailers, which is why they are taxed additionally.
Also, although buses and trains charge per user, they are also heavily subsidized.
I believe my statement was quite clear. Public infrastructure should not be a la carte.
"Buses and trains" are included in "Public Infrastructure". At least by my definition.
Hermits living in the woods, alone? Hunting their own food, making their own furniture, etc?
It seems like anyone with even the most minor connection to society are using the goods and services of the road infrastructure. Am I missing something obvious?
If you're making the common argument that they're still "using" it because they patronize stores whose goods arrive by roads and such, that doesn't really make a lot of sense. You want the direct users of something paying for it. If the non-car-owner benefits from the roads through stores using them to ship goods, they should pay for that as part of the price of those goods.
I disagree though that they shouldn't pay for it. Everyone should. However, the most likely scenario is paying indirectly, in your case.
Eg, if we increased road taxes and applied them only to those who actually use the roads directly, then shipping products will also require price increases to cover said increased road costs. So the end user is paying for the taxes whether they like it or not, in most cases.
The argument that you benefit indirectly could be applied to almost anything. You benefit from the computers used by the businesses you patronize, so should we levy a tax to pay for them? Probably not.
Nearly everyone will use the road infrastructure - even indirectly (see: buses, groceries that are delivered by truck), but users (theoretically - back to this part in a bit) have control over the amount of the infrastructure they use.
The ideal argument is that by instituting tolls (or other similar per-use pricing), people will choose to be more efficient in their use of infrastructure, either by shifting modalities (see: taking the bus instead of driving), or shifting travel behavior (see: going to the store near you instead of driving two towns away).
But, of course, this is a highly idealized model that doesn't account for negative impacts of tolling. For example, the poor tend to have disproportionately long commutes, and "consume" more road infrastructure as a result. Tolling negatively impacts this vulnerable group even more heavily than they already are impacted.
Also, the idea that people who can't afford the tolls will switch to travel modes that lessen the burden (buses, trains, carpooling, etc) presumes the existence of competent alternative modalities. This is empirically false in (most of?) America. Proposals for extensive end-user tolling would be less problematic if the revenue can be guaranteed for developing alternate modes. As it stands the vast majority of such proposals I have seen simply institute a cost without offering anything resembling reasonable alternative modes.
See Toll roads hurt the poor?
https://www.strongtowns.org/journal/2017/3/7/toll-roads-hurt...
But the trick is that NYC has multiple competent alternative modes for people to fall back to - the train (both commuter and metro), as well as an extensive bus system - not to mention the ferry system.
But more often than not tolling is proposed without reasonable alternative modes. The poor can take the bus instead of paying the toll - if the bus system was good enough to get them to work on time... If it serves their neighborhood at all.
I'm not sure if the article you linked to is specifically in regards to a specific proposal in LA - I agree with its conclusions, but I don't think you can take a "tolls don't hurt the poor" conclusion from it. Heck, the very bottom of the article literally admits "Tolls may disproportionately burden the poor".
Specifically, the UCLA graphic claims (IMO correctly) "tolling hurts less than a commensurate sales tax increase". This is absolutely correct - sales taxes are regressive and tend to impact low-income people much more than wealthy people. Tolling is the lesser of two evils here, but we can and should do better than just those two options.
There are more ways to fund transport infrastructure than just tolls and sales taxes - property and income taxes, for one, which are progressive and do not have the disproportionate impact on low-income people. Property taxes in particular help the government realize the gains produced by infrastructure investment - a new transit center leads to rising property values, leading to more revenue that can be used to maintain or expand said infrastructure.
In any case, I'm actually for tolling, but only if reasonable alternative modes are already in place. Unfortunately this means I'm against tolling in (most) parts of the US, because frankly alternative modes are either non-existent or so marginal that they are not reasonable fallbacks to driving.
In the spirit of making sure public infrastructure is maximally available and not a la carte, let's make buses and trains free to end users and funded like roads currently are.
Presumably there are no gas taxes or licensing fees in this magical place you live?
But I would like to clarify, I am not 100% against tolls.
Its perfectly reasonable to be expected to pay, for example, a small entrance fee at a national park. But it is unreasonable for this small entrance fee to fund the entire park and unacceptable for it to become a large entrance fee.
Thing bigger, friend.
(Truth be told, I'm from quite the opposite land where driving taxes finance much of the public spending. I wouldn't really mind your proposition too much.)
All in all SDCs should increase road bandwidth about 5x by my estimates.
SDCs can drive much, much closer together. They will also never be the cause of phantom traffic jams. For every human that switches to SDC, phantom traffic jams get less likely - a main cause of traffic - which again increases road capacity.
We don't have to wait until 100% SDCs to start increasing road capacity either. SDC "convoys" travel as a single unit, and interact cleanly with human drivers.
Regardless of SDCs, when road capacity is reached, traffic will happen. But SDCs have the potential to greatly increase road capacity.
No they can't, not if you want them to be safe. The biggest problem we have with human drivers, most people will say, is that humans can't drive safely. And one of the biggest reasons that is is because we drive way too close to each other. In an urban environment, it is practically impossible to maintain safe following distance: someone will slip in and take that spot instead.
Sure you might say that they can communicate with each other--they can't, not in any reasonably close timeframe for infrastructure (say, the next 30 years) where cars have to assume that human drivers are still on the road.
A worse effect is that self-driving cars are more likely to strictly stick to rules of the road and safe driving than humans are: so longer following distances, slower speeds, strict right-of-way rules when trying to make a left onto a jammed road... I don't see how they're going to be better.
This is fantasy land. This idea has been perpetuated by a few layman websites and extremely simplistic closed-loop simulations, but have never been validated by the more sophisticated traffic simulation systems used by traffic engineers. In fact, quite the opposite.
Bad reaction times contribute to waves, but waves are just annoying and feel like the cause of congestion to the driver. According to the traffic engineers I know:
1) You can't ever fully get rid of traffic waves because reaction time is only a fraction of the speed mismatch correction problem, physics still dominates.
2) You can't ever fully get rid of speed mismatches. Even a plastic bag flying on the roadway is enough to cause them.
3) Traffic waves only feel like congestion to those who experience them first hand. Minimizing traffic waves doesn't decrease travel times significantly, it merely moves congestion to harder bottlenecks like traffic signals, highway on and off ramps, or merge points.
4) Braess' paradox only manifests itself when agents are acting rationally. As rationality increases, whether through better mapping and routing systems like Waze or by algorithmic rationality of SDCs, more bottlenecks appear that didn't previously manifest themselves under a lower rationality state. Unless you can somehow centrally control SDCs (which is unlikely IMO), this will only become more prevalent.
But if you put twice, or worse 5x, as many cars on the freeways, that'll just jam up the urban core even worse than it already is. And self-driving cars are probably less efficient than human-driven cars in the urban core simply because they're much less aggressive in their interactions with pedestrians and cyclists. This is a good thing, but it will increase congestion.
Efficiency improvements can only add increase capacity by a fixed percentage. The massive improvements in cost ($0 in labour!) and convenience will cause usage to increase by orders of magnitude, IMO.
Self driving cars won't:
1. Increase their space when the traffic slows down to where there is 300 feet between cars.
2. Less accidents to cause shut downs and lane closures.
3. Merge properly instead of slamming on the brakes and putting on their turn signal 1/4 mile from the merge point. Merging will happen while moving instead of from a stop.
4. Touching their brakes even though they aren't slowing down.
BTW, I suspect that the bigger impact of self-driving cars would actually be the reduced need for parking space.
Touching your brakes to flash your brake lights when braking with your engine isn't an altogether bad idea on congested road with traffic waves – it's a good signal to the car behind that you're slowing down (before they can actually see that) so that you can together help mitigate the propagation of the wave.
Here in GA, most people don't even seem to understand that the left lane on the highway is the fast lane. Every time I'm on I-75 for more than 5 miles I'll be going speed limit to speed limit +5 and get stuck behind someone doing speed limit - 10 in the left lane. I do not believe that the majority of people tapping their brakes are doing it for a valid reason. It's more often (based on them accelerating at the same time) because they're riding their brakes.
Mathematics has shown that each time a brake light flashes it forms a wave that miles behind causes total stoppage because for 2 minutes people hit their brakes lightly slowing down with each person behind slowing a little bit more.
I've been rear-ended by people following too closely who failed to recognize that I was slowing in time to slow themselves down. I'd rather be pragmatic and warn them off before an accident occurs.
By "will be slowing" I mean: I have removed my foot from the throttle or stopped cruise control but my vehicle has not started to appreciable slow yet.
After my car drives me 45 minutes to work it still needs to park nearby to pick me up after work.
However, it hasn't been a problem in my use of taxis, rental cars, Uber, or Lyft, so I presume it won't be a problem with autonomous cars. They'll either drive themselves to the car wash when someone has an accident (spills, pees, vomits), or if for some reason a "wet" car arrives, then you'll report it, and get the next one.
Even if they didn't move the lot, my car could drop me off at the entrance and then go find an available spot. The lot is huge, close to a 1/4 mile walk from the furthest available space to my entrance. I wouldn't mind not having to worry about that on those days I'm running late.
I cannot possibly fathom how the left (which I usually include myself!) went from loving the idea of self-driving electric cars to "no! no! we need to stop people from driving at all costs!".
The amount of cars we would need as a society will equal the peak demand curve, much like electricity demand today. It will also be very likely that those cars will have multiple people in them since a large part of the cost savings will come from car sharing. In the future, we will probably have 1 motor vehicle serving 10 households, vs the almost 1:1 to 1:0.5 ratio we have here in the US today.
- cheap delivery will be used for everything - people will send and summon vehicles from everywhere. I might drive to work, send my vehicle home so somebody else can use it, summon it at the end of day, and drive home. - et cetera