17.5 Billion Hours a Year

I have done some desk-work and put together a few assumptions to see how self-driving transport adds up. What are the problems with self-driving cars or the idea behind them?

Self-driving car

Without leaving the kitchen table, I was able to identify some conceptual problems with self-driving cars and ways to improve the efficiency of car use.

If a car drives on average 12,000 miles per year and does an average of 60 miles per hour then that means 200 hours of driving per year. (Cars are spent after just 1400 to 2000 hours of use).

The occupancy rate in relation to hours per year is very low. There are 8760 hours in year. Cars are driven for 200 hours a year, typically. For 8560 hours a year a car is unused. Thus there are 43.8 times more hours of use available than are used each year. If you drove all year, you would still consume around 4 or 5 of cars.

So: let’s get more from the car. In Ireland, for example, there are 2 million cars, give/take. The year’s driving in Ireland could be done by about, roughly, 46,000 cars if they drove 100% of the time and people did not care when they arrived or left.

There are two ways of increasing the efficiency.

A) Drive all the cars all the time

B) Match the cars to the number of hours people need to drive per year.

First A: if we use the existing car fleet to its fullest, that is, drive all the cars all the time then Ireland has a driving capacity of 8760 hours a year times 2 million cars or 17,5 billion hours a year. There is not the demand or road capacity to increase usage of the existing cars to 17.5 billion hours a year in Ireland.

Second, B: let’s assume we could reduce car ownership of cars from 2 million to, say, 50,0000 cars by matching the hours driven to the cars available (fewer cars drive all the time, around the clock). That figure is not practical either.

Car use is not evenly distributed around the day. People drive much less between 18:00 and 6.00. They even drive less around the middle of period 10.00 to 14:00. So, for part of the day we seem to need a million of these cars (which are then not needed much of the rest of time). Whichever way you look at it, we can´t increase the efficiency of the existing fleet by making these cars drive more of the time or with more passenger miles.

Looking at the efficiency another way: the occupancy rate. I recall a promoter of self-driving cars saying hotels and planes would be uneconomical if used as little as cars. So, he imagined that the occupancy rate should be improved, that is when a car is in motion it carries more people.

The occupancy rate of a car in motion is 20% if you allow that most cars can carry five people but only usually car one. It is 25% for four seaters, reasoned the same way.

Twice a day traffic volume approaches the maximum and traffic jams occur (between 06:00 and 18:00 hours). Although the usage rate of cars is really low in terms of hours per year, it is at a maximum in terms of network capacity twice a day. There is considerable underuse of the cars themselves but saturation of use in terms of the volume the road network can carry. Putting more people into cars would reduce the volume of traffic.

What is the effect of this kind of efficiency?

The occupancy rate of the Irish car (or indeed any car is 20 or 25%). If it is increased to 75% (three passengers) then it would appear there are too many cars. Initially one might think that one could reduce the number of cars by two thirds but have them running at 75% efficiency (occupancy rate, not hours per year used).

The consequence of this is that dramatically fewer cars are sold. That’s possibly bad for the current model of car sales. Car manufacturers will have to sell something else.

There are peak times when car demand is high and these times often involve a door to door commute for one person which is reversed in the afternoon. Each time another person is added to the journey, the journey is made longer for all but one of those people (or all of them). See my diagram below.

Three people share a car, left side: one possible permutation.

To increase the occupancy rate to 75% will involve the car collecting three people and delivering three people. Very often those three will live and work in six places (three homes and three workplaces). Three of three passengers will have extended journey times to accommodate the other person.

A possible trade-off is that by reducing the number of cars on the road the journey time (not distance) for the two-to four passengers is shorter – this assumes all other cars are self-driving and fully-occupied.

So, if we reduce the number of cars to increase occupancy, fewer will be sold and self-driving cars that carry extra people will involve longer journey distances/times.

But if people can’t or won’t to share a vehicle with others, then self-driving cars will not change the number of cars on the roads.

If we address the efficiency of journey times by centrally-controlled traffic control systems then the “self-driving car” becomes part of a large, invisible bus-like network of planned journeys or, in theory, an ever-changing, dynamic timetabled system. Conceivably, this network will determine if you drive off immediately at 8.27 a.m. or wait in the car to accommodate traffic volume elsewhere on the route.

The self-driving car will also determine how fast one moves, again to regulate flow to avoid stoppages. So, again, even if drivers own one car and it drives them on one single A-to-B-to-A journey then the speed will be regulated. Journey times may not be very much shorter than with cars driven by humans but there will be a marginal improvement. You might spend less time in motion but more time in the car, waiting.

Citroen CX 2.5 GTI Turbo

The other version is a compound of single passenger and multiple passenger journeys as described above which is possibly a sub-optimum solution.

For an undetermined time, there will be human-driven cars on the roads plus bicycles. The autonomous system has not the advantage of the rail network which is effectively a closed system.

From out of this thining I see a few surprises.

One: that the idea of increasing the occupancy rate of cars may not require very many fewer cars as people need them at all around the same time. I imagine that at rush hour, 30% of Ireland’s cars are in motion.

Two: fewer cars are sold but more people ride in them. They will have longer journey times. Even single-passenger cars may find that the optimum journey time is longer so as to make the average journey time across the fleet shorter.

As I said elsewhere, the “self-driving car” is not adding to the attractiveness of private car use. The more effective the system is the more it resembles public transport. I like public transport very much but many people don’t. Should cars become manadatorily self-driving then many people might reason that there is not much point in paying thousands of euros a year for something very like public transport when a much smaller cost gets them 85% of the same mobility.

I can’t say this rough sketch of the issue is much more than problem-spotting but it does show that inside a plausible idea there seem to be some rather serious difficulties for both car makers and car users.

[For this think piece, I have imagined urban and suburban driving. For rural areas, average journey times are more stable as traffic density is very low. Self-driving cars would make very little difference to the overall efficiency of one-person, one-trip driving and increasing occupancy might involve very long and improbable routes for the two/three/four passengers.]

Thanks to Niels Moesgaard-Jörgensen, our correspondent in Sweden, for the conversation that led to this item.

Author: richard herriott

I like anchovies. I dislike post-war town planning.

9 thoughts on “17.5 Billion Hours a Year”

  1. The whole autonomy question simply doesn’t add up for me. In who’s interest does it actually serve? Car companies? Certainly not – if anything, it appears to hasten their demise. In a recent interview, JLR’s Gerry (IGMG and if you look at me sideways I’ll have you) McGovern suggested that in an autonomous future, design will become the key component for manufacturers. But this is fanciful. If as is suggested here, cars become more akin to public transport, all the design in the world won’t alter the fact that people will no longer aspire to own, lease or rent a car. They’ll simply hail something that will (eventually) take them where they want to go and to hell with what it is or what it looks like.

    The Silicon Valley tech companies appear to have most to gain from autonomy, as I suppose do governments – in theory at least. And this is the problem as I see it. It’s all theoretical. (politics alert) It reminds me of the so-called Brexit debate here in the UK: ‘Lets do something radical, possibly damaging, but certainly irreversible. We haven’t really thought all the implications through, because let’s face it, the whole thing is so mind-bendingly complex that would take years and years and we really just want to get on with it. But don’t worry, everything will be fine.’

    There appears to be a blank assumption that autonomy will do all its cheerleaders claim and the public will embrace it, but the public, as we’ve seen of late are fickle and while many view the concept of autonomy positively now, it may well be a different story once it starts to become a reality and the implications become apparent, since as we’ve seen, a sizable (and growing) swathe of the population don’t appear to like the idea of ceding control in any aspect of their lives.

    Another point raised here is the notion of sharing. One of main reasons people own cars is they don’t want to have to share. The car is their space and if they were to share it, they might as well take the bus. So while car sharing would do much to ease congestion, it goes against the nature and preferences of the majority.

    What I’m getting from this is that we’re simply changing one messy, imperfect model for another. One however, which increasingly appears to proscribe the very freedoms that the automobile was invented to espouse. If we calmly and carefully decide as a collective to do this, that’s one thing, but if we are sleepwalking into an irreversible paradigm shift, (as we appear to be be), that’s quite another.

  2. A whole day and just one comment (but what a comment!) – I’m astonished.

    Autonomy is an even bigger matter than the shift to electrification. and it’s creeping in by stealth already. But as Eóin says, who has asked for it? Members of the driving public, the ordinary motorists, even those who don’t like driving and are not much good at it aren’t clamouring for self-driving cars.

    Why are governments supporting the idea, apparently without question? There are rich pickings for conspiracy theorists and libertarians here.

    My own thought is that autonomous control of vehicles could become the Wankel engine of the 2020s, but on a massively larger scale. Billions spent on software, mapping, technology licensing and IP protection, and then it all falls apart in a morass of fatalities, lawsuits, and traffic disruption on an unprecedented scale.

    Then there’s the matter of trust. Vehicle makers continue to lie, cheat, default and simply disappoint. They have yet to perfect the ideas Otto, Diesel and Levassor gave their industry. Should we trust their hands on the wheel and feet on the pedals?

  3. “Cars are spent after just 1400 to 2000 hours of use”.

    Richard – that got me doing a few sums.

    In western Europe, most employees are contracted to do 1800 hours of work per year, less for the bone-idle and workshy French and Germans. So is the human constitution 70-80 times stronger than a car’s? (I’m applying David’s numbers in Psalm 90:10; where’s the progress in 3000 years?)

    At one time I had a 3-4 hour daily commute and a further 3-400 miles of business driving per week. Despite my Stakhanovite efforts, I never managed to “spend” a car, not even the Tipo or K series engined Rover.

    The accepted standard for design life of major passenger car components is 300,000km. (186,000 miles)

    At an average speed of 60km/hour, that gives 5000 hours. I suspect that’s generous – last time I checked the trip computer of my daily driver I’d managed 43.2 km/h average over a few months normal driving – and I avoid short journeys like the plague. My favoured VAG specialist has two Passat B5.5 1.9TDI loan cars which have done 470,000 and 560,000km. I’ve only tried the low mileage one, and it gave me a new respect for these cars.

    The durability of cars is a complex matter, and it varies widely between nations and continents. There are lots of factors; taxation, affordability of new cars, supply and demand, roadworthiness testing regimes, social attitudes – I could go on, but mechanical durability is well down the list.

    1. I note your figures though I don’t think they undermine my point. We have cars that are underused and to use that capacity would choke the roads and to reduce the over-capacity is a bit of a problem for anyone intrested in selling them.

  4. An interesting hypothesis, and three very good responses. I’d have to agree about the low average speed most cars experience. The journey I take most is 21 km in one direction, and that takes place on a two lane country road, a motorway, a harbour bridge crossing and then in full city traffic. Maximum posted speed only 100 km/h, some at 80, 70 and yes 50 for the country road. The best I’ve ever done is 17 minutes, which if observed by a policeman would have been worth a speeding fine ten times over, but Mum was in hospital unexpectedly. Normal is 23 minutes speeding just a bit. Then in winter you have to add time up to ten minutes not counting warm up. In 33 years, I’ve experienced no abnormal mechanical car repairs due to age bar dampers, only body rust and normal servicing plus whatever bits Audi and Subaru underengineered. Zero engine and driveline problems other than Subaru wheel bearings and electrical disasters on Audis. No new car owned less than seven years, one leased and a used Subaru that was eight years old to begin with. I’d say my average speed is well under 40 km/h.

    The problem I see with autonomous vehicles (AVs), is that it merely allows us to continue the wasteful way we design cities. Even here where I live outside a regional centre, itself in the middle of nowhere, this miniature version of business for some reason requires all the skyscrapers and major office buildings including federal and provincial governments to be in the “downtown”. I argued against our new HQ being placed there and lost in 1995. There is no parking, the place first being populated in 1749 and laid out for conditions then! When everyone walked and the train station had to be somewhere, well, having a downtown was fine. But hardly a soul even thinks about why they trudge to work in cars to this small area every day, enduring silly delays at rush hours. They would like AVs to relieve them of the drudgery, but parking would still be an issue even for ride-sharers.

    I see the same pattern everywhere I’ve been. A central core of the city invented for times past, and never updated for the increased mobility trams, trolleys, buses, then cars afforded society. No, the central core land increased in value instead driving taller buildings to compensate, and still no real area put aside for parking, which AVs will not reduce. It all becomes a nightmare as population increases. So what do they do? Put in higher apartment/condo buildings nearer the core for the wealthier to inhabit so they don’t have to drive far, or if they were of a mind to, actually walk up to two miles. People don’t trust buses, in fact some jobs require you don’t travel by them because of lateness arriving at work on a random basis! The rest of the slothful public lives miles away in suburbs or exurbia and endures the commute by car.

    Surely, if we were honest with ourselves, these city business cores would be dismantled and firms dispersed a few miles, making travel by car much easier at rush hours (I don’t see typical work hours changing much – we sleep and we are awake by biologic design).

    So instead of addressing the real problem, the techies think of ways to promote its continuance by inventing AVs, a rather top down method that still requires vast resources better used elsewhere. Car companies afraid of Luddite labels decide they have to be in on the game, so now there must be at least 2o different companies beavering away inventing autonomous systems. A bigger waste of resources is hard to imagine. There are still issues of cost for decent sensors, for example Volvo cannot reliably identify kangaroos as the Swedes use cheap sensors (no Mobileye) and hopefully smarter logic.

    So in the next five years, we will have foisted on us 20 odd Mark 1 beta 0.6 badly coded underdeveloped rushed-to-market autonomous driving programs of no merit whatsoever, touted as “leading edge” and all different with their individual pluses and minuses. It’ll be 1985 Windoze multipled by hundreds of times more coding, and cheap sensors, because they have to be affordable to equip cars. Viewed objectively and not by the business dreamers and futurists predicting a fantastic new dawn because they haven’t got a technical clue, this to me is akin to taking your very first swim by doing Dover to Calais with little to no practice. To me it’s ridiculous to start out this way, promising much and guaranteeing little. Autonomous cars will be useless unless they are really autonomous, so-called level 5, because your average pleb will be like that person who crashed his Tesla into an artic believing Tesla’s Autopilot (ha bloody har) was perfection. We’ll get level two and three to begin with which require constant human monitoring. Why bother, when they can’t even do nav/infotainment systems properly now half the time with their horrendous interfaces? So I agree with Robert that this first phase is unlikely to last due to failures, while all the tech snoots will have go back to their metaphoric drawing boards and spend some real time doing it right. And we haven’t even mentioned hackers having a go at all these connected cars.

    Perhaps about 2045 it’ll all come good. But bad city design will no doubt still be with us.

    1. Thanks for that message. Indeed, there are quite dramatic problems with the coding, regardless if nano-computing can speed it up. Faster errors, then. Even allowing good programming and fast computing, the “drivenger” will be in a form of public transport, and essentially made to wait.
      About cities, the CAIM architects made the same observations and decided that urban functions should be separated and designed for free-flowing traffic. Pretty much ever after most new urban area have been designed on that premise and many contend it hasn’t worked out very well, yours truly among them. My view is the reverse of yours: rebuild suburbia for much higher densities though no high-rise, please.
      Where we do agree is that high-density city centres are a big problem.

    2. Thanks for the response. I think I’ve been misinterpreted or I wasn’t clear. I’m not suggesting that new roads be designed for free-traffic flows above all else. Somehow. That scarcely ever works because the basic problem I identified hasn’t been cured – that of over-concentration of workplaces. No, I’m saying if you redistribute large office areas, the roads without change will handle the required flows due to the lower needs for any given road to accomodate more than the maximum share of cars originally envisioned. It’s better use of existing infrastructure of roads I’m after and a reduction of peak traffic flows. See what i mean?

  5. A rather different vision of the driver-free mobility future from TTAC:


    ” Airplane interiors experience havoc within the first hour of a flight as the worst of us begin defecating into the seats, too lazy and weak to control ourselves.

    Autonomous taxis aren’t likely to endure better treatment. Without a driver present, the urge to have drunken sex will be far too strong — and those odds only increase when you add a second occupant to the equation. With nobody watching, we’ll leave half-consumed hamburgers and cans of sweetened tea on their floors that will roll around and turn the carpet into a sticky magnet for larger pieces of garbage.”

    1. I bought my first car in 1967, used and rusty, precisely to escape the rigours of public transport at rush hours. A three-bus hour and a quarter trip in sweltering smelly heat, or inadequately heated in winter conveyance continually worsened by opening doors releasing heat was a form of mind-numbing torture for me. I tried and failed to sustain that mode of transport. The car did the trip in 25 minutes, had opening windows for summer and a heater for winter. Anyone who could afford it did exactly what I did. The TTAC article (I read the site everyday) is spot on – look at how many people treat rental cars. If there’s nobody around to object such as the owner/taxi operator, yes we can expect people to act like utter dopes. It was ever thus.

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