Traffic Congestion and City Design

I have Thoughts about city design and traffic congestion, so I will write a blog. In terms of background, I did a bunch of transport economics when I worked at Hyperloop, including building a predictive demand model (yes, really!). I’ve also traveled to about 50 countries and taken every mode of transport imaginable from unicycle to helicopter. I lived in LA without a car for 7 years, walking or cycling everywhere. That said, I’m not a credentialed traffic engineer or town planner, which might not be a bad thing in this case.

Let’s not bury the lede here. As pointed out in The Original Green blog, the entire city of Florence, in Italy, could fit inside one Atlanta freeway interchange. One of the most powerful, culturally important, and largest cities for centuries in Europe with a population exceeding 100,000 people. For readers who have not yet visited this incredible city, one can walk, at a fairly leisurely pace, from one side to the other in 45 minutes.

Florence Italy and an interchange in Atlanta at same scale. Image credit: Steve Mouzon.

Ancient, or even pre WW2, cities had their challenges, but walkability was generally not one of them. The fundamental issue is that humans and their cars are incompatible uses of the same public space, and cities built around cars will always be congested. Throughout this post I’ll explain the various interlocking “whys” that lead inevitably to this conclusion, but the fact remains. There are thousands of cities on Earth and not a single one where mass car ownership hasn’t led to soul-destroying traffic congestion. It’s not a freak occurence.

Cars are amazing

Imagine there existed a way to move people, children, and almost unlimited quantities of cargo point to point, on demand, using an existing public network of graded and paved streets practically anywhere on Earth, in comfort, style, speed, and safety. Practically immune to weather. Operable by nearly any adult with only basic training, regardless of physical (dis)ability. Anyone who has made a habit of camping on backpacking trips knows well the undeniable luxury of sitting down in air-conditioned comfort and watching the scenery go by. At roughly $0.10/passenger mile, cars are also incredibly cheap to operate.

Culturally, particularly in the US, cars are freedom. Even broke teenagers can access sufficient resources to buy an old car, and then 4 million miles of roads are immediately accessible, without even getting a passport. A lifetime of adventuring!

I hitchhiked thousands of miles in foreign countries. I’ve hiked hundreds of miles on foot. I need no further convincing. I own a (electric) car, I drive it joyfully, albeit respectfully.

Cars are terrible

Why are cars terrible? Fundamentally, they are 1000x bigger and heavier and faster (in terms of kinetic energy) than humans. They’re the only private property that’s legally protected occupying public space indefinitely. They ravenously consume public space, requiring huge, expensive roads and parking lots everywhere. For any city over a certain size (perhaps 50,000 people or so, depending on geography), car usage results in traffic congestion and demand cannot be saturated, regardless of expenditure.

While LA never completed its original freeway plan, Houston and Atlanta certainly tried. Some American cities have nearly 60% of their surface area devoted to cars, and yet they are the most congested of all. Would carving off another 10% of land, worth trillions in unimproved value alone, solve the problem? No. According to simulations I’ve run professionally, latent demand for surface transport in large cities exceeds supply by a factor of 30. Not 30%. 3000%. That is, Houston could build freeways to every corner of the city 20 layers deep and they would still suffer congestion during peak hours.

Why is that? Roads and freeways are huge, and expensive to build and maintain, but they actually don’t move very many people around. Typically peak capacity is about 1000 vehicles per lane per hour. In most cities, that means 1000 people/lane/hour. This is a laughably small number. All the freeways in LA over the four hour morning peak move perhaps 200,000 people, or ~1% of the overall population of the city. 30x capacity would enable 30% of the population to move around simultaneously. This seems crazy, but have you seen a stadium?

It is not particularly revolutionary for me to say this. Most European cities experimented with car culture after WW2, and found that a) they could not afford it and b) it was not compatible with their existing city plans.

Amsterdam found that diluting traffic by putting humans in cars choked their roads, and went back to pedestrianized streets.

Amsterdam before cars, during cars, and after cars.

Copenhagen could not afford to build and maintain enough roads for cars, so decided to spend what little they had on improving cycling infrastructure. Not only is the public cost, in terms of per passenger mile, roughly 100x lower for really good bike roads, the road capacity is much higher and, in Copenhagen, bicycles are usually faster than cars for any given point-to-point journey.

Pictured below is peak hour congestion in Copenhagen, with traffic density and door-to-door transit times excelling what could be achieved by a 20 lane highway. Spacing between the bicycles, while underway, is a few meters, compared to 100 m for cars with a 3.7 m lane width. Bicycles and pedestrians take up roughly the same amount of space.

Bikes aren’t perfect, and have their own problems. Ever ridden one in the rain? But at least humans on bikes don’t take up half the city’s footprint so there isn’t a fundamental density mismatch as humans swarm into parking garages and suddenly take up 1000x as much space.

It is also darkly hilarious to me that despite the fact that building really awesome, safe, and effective cycling roads is 100x cheaper than cars, for the same net throughput, the standard US approach to cycling roads is to throw a paint strip on the ground, then carve out exceptions to negligent homicide for drivers who murder cyclists with their cars. Hmmm.

I don’t mean to come across as an excessively granola-chomping hippie, but as a parent of young children it continually amazes me that 90% of the public space in any given city is a road, given over to cars, and as dangerous to any pedestrian as lava. But nowhere near as cool as lava. And that’s not even including weird manifestations of car culture, which sometimes seems to pride itself of outsized aggression towards any other road user who isn’t driving a car, or even a particular make of car.

When I cycled routinely to commute to work, roughly 50% of cars would give me enough space, 49% would be indifferent and get too close, and about 1% would actively try to run me off the road. I was the only member of my team at work (most of whom cycled) to never be hit by a car, though I had close calls about once a week. Cycling is a form of exercise that is beneficial for your health, up until the point where you get run over, at which point the net lifetime benefit runs negative.

It is laughably cheap to make roads much safer for bicycles and pedestrians, but even today the apparent best use of public money is removing pedestrian crosswalks.


In addition to being fundamentally incompatible with a livable city, dangerous, and expensive, vehicles also make a huge quantity of pollution. Enough to cause easily measurable reductions in life expectancy, IQ, and health of people who live in major cities, or particularly close to freeways. A lot of this pollution is car exhaust, but even electric cars shed microplastics from their tires, make noise, and choke the roads. In addition to making people sick, vehicle-related air pollution is also gradually warming this planet, until it eventually melts the polar ice caps and drowns coastal cities under rising sea levels. In that sense, then, I suppose over-dependence on cars is a self-limiting problem.

Why are roads so expensive?

Roads are expensive to build, to maintain, to operate, and also in terms of opportunity cost for finite land within cities. They’re also horrendously expensive in terms of lost time for people who spend their lives stuck in traffic on them. Why?

Like a lot of public infrastructure, the cost comes down to patterns of utilization. For any given service, avoiding congestion means building enough capacity to meet peak demand. But revenue is a function of average demand, which may be 10x lower than the peak. This problem occurs in practically all areas of life that involve moving or transforming things. Roads. Water. Power. Internet. Docks. Railways. Computing. Organizational structures. Publishing. Tourism. Engineering.

This effect is intuitively obvious for roads. Most of the time, the roads in my sleepy suburb of LA are lifeless expanses of steadily crumbling asphalt baking in the sun. The adjacent houses command property prices as high as $750/sqft, and yet every house has half a basketball court’s worth of nothing just sitting there next to it. Come peak hour, the road is now choked with cars all trying to get home, because even half a basketball court per house isn’t enough to fit all the cars that want to move there at that moment. And of an evening, onstreet parking is typically overwhelmed because now every car, which spends >95% of its life empty and unused, now needs 200 sqft of kerb to hang out. Most of the time, the road is far too big, and the rest of the time, it’s far too small.

People often underestimate the cost of having resources around that they aren’t currently using. And since our culture expects roads and parking to be both limitless, available, and free, we can’t rely on market mechanisms to correctly price and trade the cost. Seattle counted how many parking spaces were in the city and came up with 1.6 million. That’s more than five per household! Obviously most of them are vacant most of the time, just sitting there consuming space, and yet there will never be enough when they are needed! Across the US and through much of the world, mandatory parking minimums jack up the cost of new building construction. Meanwhile building codes have evolved, often inadvertently in response to other issues such as fire safety, to render more traditional inner city housing configurations simply illegal to build.

But even if roads were uniformly used at all times, they would still be expensive. Why? Cars are big and heavy and fast, so roads that carry them have to be engineered to support it. There’s a reason that furniture can be made of spindly pieces of wood, but every freeway overpass has thousands of tonnes of steel and concrete in it. The per capita cost of all the roads we barely use, and even then only on sufferance, and even then hating every minute, is staggeringly high.

Induced demand is a real thing

Ah, the days when Elon was only posting about obscure traffic minutiae.

One factor explaining why roads are always congested is their inherently low capacity. We’ve covered that. Add another lane for $10m/km (on a good day), move another 1000 people per hour. Seems like a bad trade.

There’s another reason why roads are always congested, and it’s induced demand.

First, road utilization is set by supply and demand. The supply is fixed, at least on any given day, and so demand sets overall utilization. Latent demand, as explained earlier, is probably 30x the current capacity, so why do only 3% of people who want to travel actually drive? The rest opt out to avoid traffic. The 3% represents a residuum who are compelled, over and above their objection to traffic, to get into their hated cars and endure the hated traffic. In cities with dormitory suburbs and poor commuter rail options, this means everyone who needs a job with regular hours. The traffic congestion is only limited by the marginal commuter who just cannot handle it and opts out. Since, if you’re stuck in traffic, this person is less desperate than you, they can be hard to understand. But they are there, millions of them.

Adding more roads or more lanes doesn’t fix congestion. It just allows more desperate people to travel and once again, congestion will get as bad as it needs to to squeeze out enough eager travelers – which is pretty damn bad.

To the extent that driver assist features such as autopilot or self driving reduce the pain of traffic, traffic will increase in response. Pain will remain constant, because only pain keeps the marginal extra driver off the road.

What’s worse, public spending on transport is not unlimited, so spending on additional roads (which is an incredibly unproductive use for public money, even though it is politically popular) tends to undermine competing transport modes, driving yet more dependence on cars for transport in the city.

Elon commented that if induced demand was real, then deleting roads would reduce traffic. What a crazy thought. And yet, in every single freeway removal project, this has occurred. Not to be too snarky, but it’s almost like we’ve run this experiment 1000 times in cities in every country on Earth and we’ve always had the same result, and the result is “spending money on reducing traffic congestion is a waste”.

Boring Company

Boring Company, among other private tunneling ventures, should not worry too much about saturating demand. If roads are actually priced, such as with congestion pricing in a private tunnel network, then of course congestion can be reduced – for the 1000 or so people per lane per hour that can afford to buy in. Elon sometimes talks about digging enough tunnels to solve congestion in a city – I doubt this can be done, and if it could, it would be bad for the tunnel business.

There are about 15,000 miles of lanes in Los Angeles alone. To saturate demand, we’d need to increase this to 450,000 miles (>10% of all roads in the US right now). If Boring Co’s super TBMs can do one mile per day for <$1m/mile (which would be about 10x better than current state of the art commercially available TBMs), then it would take a fleet of 20 TBMs about 60 years to finish the job, at a total cost of $7.5b/year, assuming they don’t run out of rocks under LA. I’m not going to hold my breath.


I love trains. Metro, commuter rail, suburban, intercity, international. I’ve taken intercity trains in China, Japan, Russia, Vietnam, Australia, US, Cuba (!), and all over Europe. I cannot get enough of them. But when I did economic modeling at Hyperloop, I finally understood why rail has lost transportation marketshare since the 1930s, with more than half of all routes closing in the last 100 years. Why?

There are a few reasons. Some are similar to car economic problems, with peak and average demand variation, particularly for commuter services. But I think the fundamental reason is that compact diesel engines got, if not good, then acceptable, in the 1930s. After that, shippers could move freight in almost any form factor between any two points directly. Even in 2022, freight by rail is much slower as rail cars must wait in yards for trains to be assembled.

There is another direct issue with trains, which is that rail systems are, by their nature, one dimensional. Any disruption on a rail line shuts down the entire line, imposing high maintenance costs on an entire network to ensure reliable uptime. To add a destination to a network, an entire line must be graded and constructed from the existing network, and even then it will be direct to almost nowhere.

Contrast this with aircraft. There are 15,000 airports in the US. Any but the largest aircraft can fly to any of these airports. If I build another airport, I have added 15,000 potential connections to the network. If I build another rail terminal and branch line, at significantly greater cost than an airstrip, I have added only one additional connection to the network.

Roads and trucks are somewhere between rail and aircraft. The road network largely already exists everywhere, and there aren’t any strict gauge restrictions, mandatory union labor requirements, obscure signaling standards, or weird 19th century incompatible ownership structures. Damage or obstruction isn’t a showstopper, as trucks have two dimensions of freedom of movement, and can drive around an obstacle. In Los Angeles during the age of streetcars, a fire anywhere in the city would result in water hoses crossing the street from hydrant to firetruck, and then the network ground to a halt because steel wheels can’t cross a hose or surmount a temporary hump!

Building a metro system in an existing dense city is also great (if we can avoid cost disease) but for most of the cities in the US, the suburbs are already not walkable enough to enable non-vehicle transport to a neighborhood station. The suburbs of LA will never be able to depend on a Manhattan or Vienna-style underground railway.

Buses have higher passenger density but also have their own drawbacks, although I have seen them work quite well in cities with thousands of deregulated routes. Uber got close to copying that in the US, but then we had a respiratory pandemic…

How to fix it?

I’ve spilled a lot of ink complaining. My intention here was to describe the complexity of the problem. Cars got most of my attention, but they’re also the major challenge in cities today. There are no easy fixes. But I can’t just complain and not offer any solutions!

The most cost-effective approach to reducing traffic congestion for people who live in large cities is to take our big, nebulous suburban tracts and add condensing nucleuses to them. Densify walkable urban cores, and exclude cars from them. With the right policy, even a city as pathological as LA (which I love none the less!) could turn into a much more livable city in as little as a decade.

LA 2030 would, on an area basis, look much the same as it does today. But in addition it would have hundreds of incipient renaissance Florences scattered across the basin. Many of these cores are already there, such as Pasadena old town, or Anaheim, or downtown LA. These were walkable cities before the post WW2 urban sprawl. Many of them already shut down some lanes of traffic to provide space for outdoor dining during COVID. Don’t stop there! Keep going!

We already excluded cars from Santa Monica Mall. It worked well. Why not do it again?

Ideally, in each of these urban cores perhaps only a mile wide, tens of thousands of people could live and work and play locally, living in modern low and midrise apartments. Not much benefit to buildings taller than about six floors. Roads still exist for buses, bikes, truck movement (ideally at night), emergency vehicles, and accessibility, but instead of 6 lanes of deafening traffic and onstreet parking, and a five foot strip for foot traffic, two lanes of sinuous road for motor vehicles and the rest for everyone else who lives there. Trees. Outdoor dining. Children playing without risking their lives.

How to reduce congestion? Why do people leave their houses? Work. School. Medical. Shopping. Play. There is no reason that 95% of the tasks people do outside their house can’t be within three city blocks. Then there is simply no reason to scuttle down into some cavernous, poorly ventilated underground garage, motor some gargantuan car out onto the traffic choked roads, and spend hours of your life every day merely to get to some other expensive garage to go into some otherwise indistinguishable piece of real estate.

It’s not hypothetical. Hundreds of cities worldwide, even in 2022, still operate by this playbook.

In between these urban cores, the suburbs are still there. People who like them can live there. If they want to come to the nearby town they can take a train or a bus or cycle (ideally on an actual bicycle road) or drive and park nearby, then walk in. No-one has to sacrifice the American Dream!

57 thoughts on “Traffic Congestion and City Design

  1. Long term the solution will be Musk’s self driving cars
    These will
    Make cycling easier and safer – E-Bikes also help
    Remove todays ownership model – you will simply call for a car
    Because they are safer and not “personal” a “car” will be able to shrink it less than 1/10th the weight of a modern car
    Self driving city cars that are much smaller and self driving will also be able to drive much much closer together and faster


      1. I’m cautiously optimistic about self-driving cars. They should be able to improve throughput somewhat, by having less unpredictable braking and lane-changing, and they should be able to reduce the amount of space used for parking.


  2. The key idea that excites me about Boring Company tunnels (or really any new-construction physically-isolated limited-access private roadway) is the potential to require all vehicles on it to be part of a unified networked control system. In particular, your estimate of 1000 vehicles per lane seems about 10x lower than should be easily achievable and safe for a protected lane of cooperating cars. 10k vehicles/hr would give ~300ms for each car to notice if the one in front starts slowing down, which would be difficult for AI based self driving, but is no problem for a simple control system or cooperative networking. The physical limit is closer to 20k/hr, and increases with speed.
    If you divide your boring company estimates for LA by 10, they start looking a lot more reasonable.


      1. That doesn’t seem correct if you are building a network of tunnels where the entire traffic isn’t expected to enter/exit at one end. I agree that the ingress/egress capacity needs to scale with the throughput of the system, but the ideal solution seems to be doing that by adding more small entrance points closer to the origin/destination of the trip, rather than by making each entrance/exit larger. That’s the key difference from something like a subway system, which also needs ingress/egress capability to scale with ridership but is forced to use a few very large stations because each additional station implies a slower journey for _every_ train.

        To come back to the comparison to the current LA road system, I read your initial claim as being something like “carrying 10x more traffic than LAs roads currently do requires 10x more tunnels than we currently have roads”. I dispute this on the grounds that there are currently lots of roads that never exceed 1/10th capacity (i.e. anything serving <100 houses) and so don't need to be changed, and the relatively-arterial roads where that's not true mostly get replaced with high-speed single protected lanes that can handle vastly more throughput, not with large numbers of low-speed lanes. The interface between those systems happens where the demand is <=1 full low-speed lane, not where it's 1 full high-speed lane.


      2. Assuming surface street capacity of 1000cars/hr, 100 houses could all decide to leave in the same 10min window and shouldn’t max out the throughput limit. If you’re thinking of congestion because the line of cars is backed up all the way from some larger artery, then that’s a separate problem. If you’re thinking of substantially larger roads being “local” (5-10k houses), then the entire point is that as we try to increase transit usage and decrease congestion, we can do so by moving the definition of “local road” closer and closer to your final destination, rather than by trying to make those local roads higher and higher capacity. For something like Boring Company tunnels, this moves towards having multiple tunnel entrances in a single “neighborhood”, but that still should require many fewer miles of tunnels than the miles of roads needed above ground.


  3. Ah, Casey, you are thought-provoking, as usual. A couple of observations:

    1. My city (Oklahoma City) is not terribly congested, but it is quite large in area (in fact back around 1970 or so it was the largest city by area in the US). People I’ve worked with from other places have comemented on how our well our expressways are laid out to efficienctly get from place to place. We lost a lot of downtown to the urban renewal plan from hell, but over the past couple of decades have concentrated on rehabiliting it for business, entertainment, and residences. A great deal of the space is in refurbished old buildings. As part of the plan we committed to a streetcar for downtown / midtown and nearby. The idea is for people to park anywhere near the streetcar line and the use the streetcar to get around within downtown. Many young families have moved into the area, and before Covid the place was humming.

    I love trains also. In 2004 I needed to travel from Tulsa to Washington DC, and decided to give Amtrak a try. Had to take the bus to Kansas City, then Amtrak to Chicago to connect with the train to DC. It was a lot of fun, even though the weather and having to give way to freight trains made the DC train about 8 hours late. I think most people here in the wide open spaces are just not patient enough to wait for public transportation – they want to be able to jump in their car and go at any time of the day or night. The 12 minute intervals between the streetcars downtown are no problem though, and it’s interesting to see how many new businesses and restaurants have grown up around the streetcar route, somewhat like towns growing up along the rivers in our past.

    2. There is a lot of attention to EVTOL Urban Mobility these days. Two modes seem to be evolving: EVTOL terminals and point to point. One of the latter mode vehicles under development seems promising: Kitty Hawk Areo’s Heaviside. The prototype is a single place fixed wing aircraft with props that can rotate to provide vertical operation. The fixed wing makes it more efficient than something like the octocopter; it operates with a remote pilot, and can also fly autonomously. The FAA and related industry are actively working on the technology and rules to ensure the separation necessary for safe operation.

    Liked by 1 person

    1. I’ve heard good things about Oklahoma City, and I would like to visit. But the population is pretty tiny by city standards. Even relatively large cities such as Columbus Ohio or Austin Texas have less catastrophic traffic than LA!

      EVTOL is cool but it won’t solve congestion at scale. The vehicles are still very noisy and disruptive, expensive to build and operate, fundamentally limited in range and cargo, and so on. I see them, at best, falling into a segment like motorcycles. Sporty but niche.


  4. “ Not much benefit to buildings taller than about six floors.” – what is the tradeoff that makes more floors not worthwhile?

    Thoughts on whether Amazon (reducing the need for physical stores) and Zoom (reducing the need for physical office space) will change some of these equations? I realise the former has costs of its own (so many delivery vans!) and the latter only applies to a small slice of the workforce.


    1. Delivery vans are much more efficient than everyone doing their weekly shop.

      6 floors. Supertall residential towers lack street access, while elevators consume footprint. There are also very few successful communities built around very tall residential buildings. The net person density doesn’t improve much beyond 6 floors.

      Liked by 1 person

      1. The community point is an interesting one. Very small blocks can be self-managed, which presumably forces some interaction that builds community (as well as there simply being fewer people to meet before you know everyone).


      2. I do my weekly shopping by walking with a collapsible cart. Not everyone can haul their week’s worth of groceries up the stairs as easily as I can, though. Elevators would help with that.


  5. I would expect most of the gains from density to come from fairly modest increases, just as going from 20 mpg to 30 saves more fuel than going from 30 mpg to 40. So six floors versus taller isn’t a big deal. However, I’ve lived in a 14-story building and a bunch of five-story or less, and fourteen seemed like a better height than six. Going up three or four flights of stairs is enough, when you’re carrying groceries or furniture, and the elevators didn’t seem as though they took up that much space compared to the apartments, nor were the elevators themselves congested.


  6. My thought process with Boring Co. is that, as the production of tunnels becomes privately available and cheap, the issue we have regarding competition between different transportation systems lightens up. If it costs X/mile to tunnel, the most profitable options (high throughput) will be used. I expect in 50 years this will be how a lot of US cities get their subway systems.

    I do also like the concept they provide in one of the videos, an autonomous mini-bus. That intra-city transport/throughput seems a nice balance between throughput and granularity, where lower demand routes can easily be addressed. In fact, with some sort of standardized app where citizens schedule their plans for transport, I bet it could be further optimized.


  7. Why is nobody discussing the possibility of just encouraging companies to adopt flex time policies that distribute the traffic throughout the day, rather than in two big lumps? I’m fortunate in that my employer doesn’t care exactly when I arrive or leave, so long as I get the job done, and am present for a core period to be available for meetings, and I find that even a five minute shift in when I do my commute hugely impacts the amount of traffic I encounter.

    It seems to me enough is being spent on the roads that the incentives here could be pretty significant, and still be more cost effective than building more roads.

    Liked by 1 person

  8. I think eVTOLs is the radical solution. Since they only need infrastructure at the nodes of the network, they can bypass congestion by spreading out in 3D-space when going between nodes.

    Very unlikely for existing cities though since the congestion, and especially noise, would be too great at the nodes. But it looks feasible at lower population densities where you could still get an equivalent door to door travel time due to their higher speed.


    1. I mentioned Kitty Hawk’s Heaviside EVtol in my earlier comment. They have done a lot of analysis of what a practical urban EVtol would look like:
      * During flight testing their prototype has demonstrated range of 100 miles and speeds of up to 180 mph, with one quarter of available electric charge remaining in its batteries for safety reserves. It requires less than half of the energy used by a conventional electric car per mile.
      * Because it is fixed wing it creates less than half the noise of a helicopter – 35db at 1,500 feet.
      * It can operate autonomously, although initial plans are to use a remote pilot.
      * It will operate point-to-point rather than requiring an EVtol terminal

      The link below is Kitty Hawk’s vision of how their EVtol might be used in lieu of Lyft or Uber.


      1. I saw that comment now, I wrote my comment earlier but didn’t get around to actually posting it until later.

        I also like the Heaviside since I only think a single seater really makes sense if you want true door to door transportation. From the videos I’ve seen it seems kind of noisy compared to the Joby S4 though – but I guess there’s a large potential for improvement since it’s so much lighter than the S4.

        Thanks for the link to the post, I’ve missed those latest updates from Kitty Hawk.


      2. The only info I could find on the Heaviside’s noise up close was an article in “Transport Up” from 2019 stating the maximum sound from Heaviside was 85 db. Assuming this is from a distance of one meter, that gives around 71 db at 5 meters and 65db at 10 meters. For 103 db at one meter the sound at 5 meters would be around 91db, and at 10 meters would be around 83db.

        Since the Heaviside is going to anounce its pending takeoff to the surranding area, and then spin its props as an additional reminder, I would expect 8-10 meters to be a reasonable distance for any passerby to maintain. On taking off the Heaviside would transition out of hover and be on its way almost immediately. Just speculating here:
        The Heavisides configuration might allow some kind of noise-cancelling tech to be used on take-off and landing.


      3. You are most welcome. As a pilot I believe electric General Aviation aircraft can’t get here soon enough. The latest engine out crash in the media was the recent Cessna 172 Haulover bridge crash – one fatality and two serious burn victims. The A/C took off from Florida’s North Perry airport, the same airport that saw a Beechcraft Bonanza’s engine fail immediatly after takeoff, the resulting crash killing the two occupants of the Bonanza and a child on the ground. Apparently the Bonanza’s engine was way overdue for maintenance, but this is the kind of situation where I see the simplicity and fault-tolerance possible with electric A/C saving irresponsible people from themselves – as well as innocent folks on the ground. I expect the battery R&D underway for drones and EVtols will benefit electric vehicles of all kinds.


      4. Asking all the pilots: won’t wake turbulence / helicopter downwash severely limit flying car/motorbike density? Wouldn’t having to avoid other vehicles’ wake correspond, as far as throughput is concerned, to all vehicles having to move in the same horizontal plane (or a series of planes spaced with a remarkably wide vertical separation)?


      5. (I hope this ends up in the right place since there doesn’t seem to be a reply button on messages if they’re too deeply nested.)

        Basil Marte:

        I’m not a pilot, but I think downwash would be a limited problem for such small aircraft since the square-cube law gives them low disc loadings.

        It should also only be a potential issue during take-off and landing since downwash is drastically reduced at higher speeds. So it might limit traffic density somewhat at the nodes, but I doubt that it would be a problem in the airspace in between.


      6. As Heaviside is a fixed wing aircraft with props/motors that rotate for vertical or horizontal thrust, the only downwash is going to be in the first 10-15 seconds of flight as the vehicle lifts off.


      7. First, I am confused by the hierarchy in the comment posting, but think I have figured it out.

        In reply to Basil Marte, as a pilot and one who did engineering work for a few decades, wake turbulence is based largely on the size of the aircraft and is tied into the wing loading, pounds(mass)/kilos per square of wing area. A large aircraft, say a Boeing 747, produces a great deal of wake turbulence which comes from the wingtip vortices. It is sufficiently powerful enough to cause problems for a moderate sized aircraft and cause very bad flight conditions for light aircraft. Air traffic is separated by a few miles from large aircraft to remove most problems from wake turbulence. As to downwash, that is a factor of thrust from the rotors. It is similar to propwash from propeller driven aircraft. The more air moved by a rotor/propeller, the greater the downwash. It does dissipate fairly rapidly, though.

        For a small commuter type of VTOL aircraft, the problems of wake turbulence and downwash would be minimal, with just the necessity of a small cleared area to prevent problems.


    2. I think a combination of Casey’s “Condensing Nuclei” and air taxis operating per Kitty Hawk’s vision would go a long way to mitigating the problem. I see each Nuclei being unique in its design and ambiance rather than built with a cookie-cutter approach.

      Modular nuclear reactors – perhaps LFTR or similar – could power a Nucleus and surrounding area, thus distributing the electric grid.


  9. What are the assumptions that go into thinking that the ultimate level of induced demand is 30x current driving levels?
    In particular, what speed of travel is assumed to be possible?
    A quick google suggests that Americans drive just under an hour a day [1] and I find it hard to believe that people would desire more than a couple of hours of travel a day even if they could go anywhere so it seems that this must rely on very high speeds, that exceed even traffic free roads.


    1. You look at how many extra journeys are taken when additional capacity is provided (eg with a new train line or freeway). This provides a measure of latent demand as a function of traveler value of time.


      1. Extrapolating that far from small-signal behavior sounds very wooly to my ears.

        If this traffic would come from increasing commute distance by a factor of 30, how fast are they going? If it would come from people taking 30x as many trips, what about the time it takes to decide to go somewhere, walk to your car, walk from your car, and do something at the destination? There’s an Amdahl’s law sort of problem here.


    2. I’m also finding this extrapolation hard to believe. Granted, I haven’t run models as part of my work, but 30x latent demand is an extraordinary number, and we know what extraordinary claims require.
      In the Chicago area that I’m more familiar with, one expressway moves 275,000 cars/day. Not much at night, so let’s call it about 75,000 for the morning commute. We’ve got at least a dozen expressways (counting beltway and connectors). It’s easy to say >700,000 cars travel on the expressways every morning. But LA only moves 200,000?
      Assuming that’s 20% long-haul truck traffic and 80% residents, that gives 560,000 residents, likely daily commuters.
      The city of Chicago has 3 million people, plus 5 million in suburbs, but most suburbanites don’t work in the city, so at the very most that’s 4 million that would potentially use the expressways, even if they were wide open. (Also remember that <1/2 the population has a job, factoring in the retired, children, stay-at-home parents, unemployed for other reasons. You're not going to go on the expressway to go to the local grocery store.)

      That would give a latent demand of 7x, and I'm using some really generous numbers there. Something around 3x would be believable.


  10. Fundamentally agree we that walkable little communities are nice, but…

    > All the freeways in LA over the four hour morning peak move perhaps 200,000 people, or ~1% of the overall population of the city.

    This is low. As a sanity check: There are 4.5 million workers who commute in LA County alone, and 80% of them drive alone to work (10% carpool). Most of those trips have freeway segments.

    Liked by 1 person

  11. I looked at the boring tunnels and thought “omg, perfect bike tracks”. No head wind, no rain, no cars. They’re ~4m wide and the studies seem to say that equals about 8000 people per hour. The last mile is sorted, as everyone has a bike. There’s no delays transitioning from the feeder transport to the tunnel transport and back.

    And it gets around the usual “you can’t take my road, I paid for it with my car registration” Bullshit.

    Liked by 1 person

  12. “There is no reason that 95% of the tasks people do outside their house can’t be within three city blocks.”

    Shopping, play, school, and possibly some forms of medical, yes, but not work. My understanding is that the whole point why cities exist in the first place is that people (and companies) want to move to the labor markets that are the most liquid, deep, and overall have the most specialization as a consequence (though different cities can specialize in different niches to some extent). Spiky density makes the most sense if the spikes coincide with nodes of the transportation network.

    “steel wheels can’t cross a hose or surmount a temporary hump”

    Sure they can:
    Related technology in use today is the “flying switch”, which I know is used by at least BKV (Budapest, Hungary) to create a temporary terminus wherever necessary due to track closures lasting several days. A switch and three adapter ramps are laid over the existing trackwork, plus a single wire is strung between the existing overhead lines.


    1. “but not work”

      Why does work have to continue to be zoned far away from housing? When almost everyone’s labor was needed in agriculture in order to just provide enough calories for survival, people had to be spread out. When most people’s labor was needed in manufacturing in order to provide a modest level of consumer goods, and controls on pollution and noise were rudimentary at best, it made sense to have jobs clustered in places that people wouldn’t want to live because of the jobs that were already there. But now? Most people’s work is done in stores, restaurants, and offices. Those can and should be allowed to be interspersed with housing.


      1. I agree that zoning laws are too rigid but there is natural incentive for people to congregate in the same space, they simply become more productive.
        Should you be allowed to live there if you wanted? IMO absolutely, but you probably won’t want that. Commercial real state is way more expensive than residential and even if there are no factories it will be louder and possibly more dangerous. Where would you feel more comfortable letting your kids outside: a residential suburb or a dense commercial/residential neighborhood with people from all over the city?


  13. Some comments on this post.

    1. Over 10 years ago, I read of a simulation done of self-driving vehicles on controlled access roadways (i.e. freeways). One point that stuck with me was that when the saturation of self-driving vehicles reached about 10% the traffic movement radically improved.

    2. I have problems with comparison of transportation in Europe to that in the U.S. I lived in Germany (West Germany at the time) from 1977 to 1980 and traveled there frequently in the early 1980s courtesy of the U.S. Air Force. While there, I traveled throughout Europe. I used public transportation there even when I had a car available. The population density and travel distance are considerably condensed as compared to most of the U.S., with exceptions for a few geographically small areas in the U.S., which makes the comparison unbalanced. One thing I noted was that many people in Europe lived fairly close to their place of employment. Another observation is that in Europe, mixed use of property (residential, retail and business) is culturally more accepted than in the majority of the U.S.

    3. Point 2 informs this comment, in the U.S. I do not believe that one will find in many urban areas that 95% of things done outside the home will be within 3 blocks because of it is just not there. And only in some older urban areas will you find small pockets of that. Resistance to change will be great because it is not in the modern American culture. In suburban areas, 3 mile might be a more realistic figure.

    4. I don’t see Electric Aircraft as a viable answer to transportation issues. The current and foreseeable power density of batteries makes Electric Aircraft non-viable. In general, though, I don’t see electric vehicles as a panacea because the U.S.’s electric generation and distribution system is far from capable of supporting a robust electrified transportation system. Perhaps a hybrid aircraft with a very efficient electrical generation capability.

    Liked by 1 person

  14. I love your work.

    Your work here is irrefutable, except through anecdote, and my point is everybody’s story is different.

    We live in a large suburb of Huntsville Alabama. My 16 year old daughter works in an icecream store 6 miles away. She comes home often at 10 or 11pm. She borrows mama’s car to get there and back. None of the options mentioned in your article are available or, if they are, they are not feasible.

    This is anecdotal, but everyone’s need is the same in a different way.

    It would be nice to have more bike paths, and these exist here for recreation, but noone would use them to get to work. There is no chance whatsoever of public transport. The cost of Uber would rule out working in an icecream store. And so on.

    Cars are sometimes a toy of the rich, or a product of “car culture”, but in flyover country they are the essential enabler of the poor and working poor. The current four/five dollar gas is a disaster for them. The ubiquity of cars may change eventually, but perhaps I’m being too pessimistic when I say it won’t change soon, nor must it.

    I wish you success on getting your ideas implemented in LA, but I hope we are able to keep the system we have in Huntsville Alabama.


    1. I have been to Huntsville c. 2005 and I take your point. That is why I began with cars are awesome. The problem is too much of a good thing destroys our lives and public spaces. Noone is going to take your car, though there is no guarantee gas will remain artificially cheap forever.

      Liked by 1 person

  15. The best solution would be ET3 or Skytran transport, witch are both autonomous vehicle on a dedicated track.
    One lane could carry 10800 up to 1300 000 car equivalent per hour (assuming speed of 54 to 6500km/h) and 5m long car equivalent.

    Small Entrance and exit will have to be build along the lanes to cope with trafic.


    1. The technology needed to support urban air mobility is already being developed. Beyond-line-of-site operations have been successfully demonstrated. VTOLs are already flying that can be remotely piloted or fly autonomously. Sophisticated path deconfliction equipment for drones and VTOLs is already available for sale. The FAA, with industry partners, is currently defining the infrastructure and regulations that will be required for large-scale use of the urban airspace. In busy airspace there will probably be defined paths, similar to standard terminal arrival procedures and departure procedures, that traffic must adhere to.

      Of course, UAM will only handle a portion of the movement of goods and people, but it will offer rapid travel from point A to point B for those who put a value on their time. On Casey’s point about building height, I believe that if one wants to live in such a dense environment as Los Angeles, tall buildings make sense. And with UAM there can be several landing pads at various points up and down the building.


  16. >And since our culture expects roads and parking to be both limitless, available, and free, we can’t rely on market mechanisms to correctly price and trade the cost.

    Why not change that? Why not let private enterprises build roads in places they judge there is demand, the same way they can build parking lots? Payment could be done automatically.

    >Buses have higher passenger density but also have their own drawbacks, although I have seen them work quite well in cities with thousands of deregulated routes. Uber got close to copying that in the US

    That is very interesting. One problem with a bus/train oriented top down planning is that public transport can be very unpleasant. Sometimes it’s full and sometimes it’s full of loud and rude people, specially in large cities. Deregulated routes would respond better to those problems instead of people having to wait 4 years and hoping the next politicians will do the right thing.

    >How to reduce congestion? Why do people leave their houses? Work. School. Medical. Shopping. Play. There is no reason that 95% of the tasks people do outside their house can’t be within three city blocks.

    One problem is that lots of those things would be of lower quality. If you had a school for every 9 blocks area it probably wouldn’t be an exceptional school. Same with doctors, malls and work. Living in mixed commercial/residential neighborhoods can also be unpleasant, it can be loud, dirty and violent.

    That’s not to say I agree with the current model. It’s very top down and people don’t have the choice to build a walkable neighborhood if they want.


    1. pt 1 – governments already build roads in places they believe there is demand. I’ve looked at the studies made when improvements in roads around me were announced. They don’t just build roads willy-nilly. Private enterprise would likely choose locations based on local wealth, with high-speed lanes for the ultra-wealthy.
      pt 2 – Sounds like you want deregulated bus routes to segregate the “civilized” wealthy people from the unwashed masses. Not sure this would help the overall economy or give upward mobility. Lifting everybody up gives the maximum benefit to the economy.
      pt 3 – Small doesn’t mean bad. I went to a small school, and there are definite advantages (and some disadvantages, especially in the pre-internet days). Small parks within reach are better than a park you rarely get to. More mom-and-pop stores instead of big box stores means modestly higher prices, but lots of places make that work.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s