Monday, March 7, 2016

Capacity Case Study

Huch wood would a woodchuck chuck?  -or-  What is the real potential of a driverless system?

Lets start the devil we know. The present "system" is fairly well studied and, for all its diversity, exhibits fairly consistant behaviors across all its forms.  Different roads, weather conditions, and vehicles notwithstanding there is a common factor-- the driver. Drivers can be counted on to take a roadway of almost any design and reduce its capacity.   Give the driver a potholed, too narrow, and winding roadway and there will be more horns than progress. Create a broad, well lit multi-lane freeway and every commuter in the region will converge on it and create a parking lot. 

The driver, not the road, creates a fairly firm bottom line. The average capacity for a lane of traffic at highway speeds is about 1,200 vehicles per hour. Above this number and slowdowns and stoppages become inevitable.  At lower speeds the number increases marginally to a max of 1500 vehicles at 45 mph, but who wants to drive 45?  The bottom line is that it is not a large number (about one car every three seconds) and that it is inescapable, largely because it is rooted in the average driving abilities of a large and heterogenous population.

A driverless system, on the other hand, is all about the design of the road and the quality of the vehicles.   Its true capacity is intimately involved in the limits of technologies we haven't even fully explored yet. Theoretically this limit might be cars moving nose-to-tail down a single narrow lane at 150 mph (35,000 vehicles per hour, give or take). The practical limit is certainly lower, but by how much is above all an engineering question.

Case Study

Trying to determine the capacity of a driverless system therefore depends on creating a plausible picture of what technical capacities might be developed in the not too far distant future (our theoretical woodchuck). The case study that follows describes a mature technology, but not the theoretical limit of what can be achieved under controlled conditions. It imagines that two of Seattle’s most heavily utilized east-west arterials are converted to allow limited utilization be driverless vehicles.  It reserves the center lane for intermittent  (one minute out of five) use by automated traffic.

       The Pulse
Every five minutes or so a "pulse" of automated vehicles would pass down this center lane (westbound on 45th, eastbound on 50th).  Special signaling will alert traffic to vacate the center lane (and complete left turns) well in advance of automated traffic. Traffic at intersections along the route would be stopped in all directions and in a sequence allowing uninterrupted passage of vehicles at a steady speed of @ 35 mph along a route stretching from the UW to Ballard neighborhood in the west. The lane would be reserved for automated traffic for 45 seconds (including a 10 second warning period) every five minutes. Vehicles would travel in groups of three tightly spaced vehicles with three vehicle lengths between groups. Aggregation and disaggregation of vehicle groups would take place opportunistically as there would be no physical barrier between traditional and automated lanes. The lanes themselves, especially at intersections, would be heavily invested with sensors and the capacity to communicate directly with vehicles.


● 45 second passing times with 10 second warning period
● Automated traffic on 5 minute intervals
● 3 vehicle in each platoon, minimal spacing between vehicles (@16”)
● Average Speed 35 mph
● following distance between vehicle groups-- 3 vehicle lengths (@55')
● total platoon length = 3 vehicles (each 18') with following distance = 110ft

● Distance covered at 35 mph (@51 feet per second) = ½ platoon/sec = 1.5 vehicles/sec
● Total Number of vehicles in transit during available transit period at 80% efficiency = 45sec x
1.5 vehicles/sec x .8 = @54 vehicle capacity per transit period
● Total hourly capacity of Lane = 12 transit periods x 54 vehicles= 648 per hour 
● 35 mph Automated Lane 24 hr capacity = 15,500 (one way)
● Actual 45th street traffic (one way)=11,000 (max @ 900/hour)

It’s a startling result. A single lane of automated one-way traffic on an arterial such as
45th street, operating for less than one minute intervals every five minutes, could nearly double the one-way capacity of that arterial. A full time automated system would have about five times the capacity.

Extending the model to an interstate with its much higher speeds yields even more impressive results, especially if we keep following distances similar to the original model.

● 55 mph Automated lane hourly load capacity = 6,400
● Typical Freeway lane, hourly load capacity= @1,200
● 55 mph Automated lane 24 hr capacity (uninterrupted)= 153,000
● Typical freeway one-way 24 hr traffic (I-5 in downtown Seattle) = 150,000

Wit uninterrupted service a single automated lane (at 80% capacity) can carry the
equivalent of five lanes of traffic, essentially the entire freeway. 


The potential capacity of a driverless system is what usually fires the excitement of
someone who wrestles with the glaring inefficiencies of the modern car based transportation
system. Much of the time this excitement leads people to look at designing fully engineered
infrastructure, things like PRT’s. While it's fun to imagine the creation of a world tailored to
our transportation needs, history suggests a different path of change. The widespread use
of driverless cars would suggest a fundamental shift in our society and culture, and changes
that big must be driven by more than an engineered ideal. That is not to say that such an ideal
will not someday be reached. The reliability and efficiency of many systems, such as high
speed rail or the aviation industry in general, could hardly have been contemplated by even
the most enthusiastic visionaries of the 19th century. But the process of change is inevitably

From my office I overlook the ship canal bridge, an important component of I-5 as it passes through Seattle. Over 50 years old, the bridge carries vehicles whose basic design is older still. A driver from 1930 could more quickly learn to operate a modern car than he or she could learn to use a cellphone. The sheer scale of this structure, and the massive transportation system of which it is a small part, seems utterly resistant to significant modification of any kind. This is the story of the last half century. Will the next 50 years to be that much different?

Possibly. Changes on this scale do happen. History give us some idea of the dynamics that drive dramatic and rapid changes. It gives us examples of the forces that impede progress for long periods of time, and then drive it forward at speed when change finally does take place. That sounds like a big enough subject for another blog post eh?

45th Street at Latona, looking west.

Saturday, January 23, 2016

Resiliency - Sustainable Transportation and Driverless Vehicles

Sustainability is usually associated with manageable problems - how to make our everyday activities less of a burden on the environment, and on each other.

But there are other problems. Big ones. Each time we watch a city (or region) respond to an uncommon but inevitable events like the East Coast's snowmageddon we wonder about tomorrow and, here in the Northwest,  the Big One.

What to expect? Well, the script is usually pretty much the same;
  1. Encourage people to prepare before the event takes place. This often involves sheltering in place as road net will inevitably jam as large numbers of people attempt to use it.
  2. Shut down the system as the event begins (the events of #1 may have already taken care of this)
  3. Wait
  4. Use emergency vehicles to get to those in desperate need.
  5. Bring in the heavy equipment to clear the road of the vehicles left behind during phase one.

On a side note; The above process also describes pretty well what happens when it snows in Seattle.

Like a well oiled machine

So the existing system sets a pretty low bar for effectiveness, but it does have some advantages
  • simplicity: each vehicle is dependent only on gas and a driver to be mobile
  • resiliency: the roads are wide and tough and there are a lot of them (about 20% of most urban landscapes are paved), even sidewalks will do in a pinch.
  • flexibility: just about any sized vehicle can use any road

What would driverless cars add to the mix? A a substantial number of autonomous (or auto-capable) cars on a road that is largely unchanged from todays infrastructure. The second is a fully autonomous system with an infrastructure largely optimized for smaller, more numerous vehicles and embedding a intelligent element in the road itself.

The first option would likely respond to natural disaster in the same way as the present system with a few limited exceptions. Driverless vehicles would be able (to the extent the roads haven't already been jammed) to move about during the event and develop a fuller, real time picture of road conditions etc. 
This would help during the rescue phase and even allow some non-drivers to escape if conditions allow. During the rescue phase some people could be moved in driverless vehicles freeing up manpower for other tasks. In the aftermath, depending on the efficiency of driverless technology, mobility might be restored more quickly by allowing only driverless vehicles into the area thereby avoiding bottlenecks etc. Otherwise, not much change from the present system....bring in the helicopters.

The second option would likely look much different. Most important would be the potential for a well designed system to move large numbers of people very quickly. Ideally this would mean more numerous small evacuations at critical points rather than general evacuations over large areas. If the system were well designed and had an extensive network it would be possible to route resources around almost any disruption ( a bit like the internet).

Of course, if it is not well designed it runs the risk of a total system failure, possibly at the disastrous moment when thousands are on the move and far from shelter. Bring in the helicopters.

On balance it appears to provide at least the potential for improving our response to natural disasters. At present the bar is set pretty low, too low, and new tools should be welcomed.

Wednesday, November 26, 2014


Driverless vehicles will return theWashington State Ferry System to its historical importance as a critical regional transportation network. Halving trip times, doubling or tripling the capacity of the existing system, all without significant changes to boats or docks.

Except that ferry facilities will take up less than 20% of the real estate they presently require.

All of which means that the Washington State Ferry system is an ideal example of the enormous disruption driverless vehicles are set unleash on regional transportation infrastructures.

Each region has its own set of unique transportation challenges, but few are as daunting as those facing the managers of Seattle/Tacoma's regional transportation network. Most serious are the numerous choke-points created by hills, canals, lakes, and, finally, by Puget Sound itself.  Moving north to south is difficult enough on the region's two (highly congested) primary freeways. But moving east to west, especially during rush hour in the Seattle urban area, is almost impossible.


These large inland bodies of water, the results of a great glacial excavation project of previous millennia, were once the primary regional transportation network. While this inland marine waterway has made Seattle/Tacoma a primary ports for trade with Asia, it also constitutes an effective limit on Western Washington regional development. 

All this in spite of the fact that The Washington State Ferry system is the largest in the US (3rd worldwide), and moves almost a million cars every year. But for all that size it serves relatively small communities on the Western side of the sound, and supports little of the economic activity between them. It seems counterintuitive that driverless cars should have any significant effect on the function of a marine highway but in this case, like many others, drivers vehicles have an outsized potential making existing infrastructure operate with an entirely unprecedented dynamism.

To understand why this is so it's first necessary to understand how the existing infrastructure operates. The ferries are fast (typical transit time is not much more than 30 minutes) and large (up to 2500 passengers and 200 cars. Overall system capacity is impressive with 22 boats carrying up to 30,000 passengers every day.  Loading times for foot passengers are quite short and anyone arriving at the terminal 10 minutes before departure he would be assured of a spot on board. But any use of transit at either end adds a significant level of uncertainty. A driver, however, would have to budget at least half an hour more at the front end ( if all goes smoothly), 20 minutes more at the backend (for unloading), and significantly longer during rush hours, holidays, and game days. 

Attending Thanksgiving celebrations on the other side of Puget Sound (with family on Bainbridge Island) will include a nearly three hour return journey (2 hours in the car line, boarding, boat ride, disembarkation, ride home) to cover the distance of little more than 15 miles. My brother-in-laws daily commute is more typical - 10 minutes bicycle ride the front end, 30 minutes on the boat, and another 10 minutes bike ride on the Seattle side - a bit more than the national average but not by much.

Not that driverless vehicles will not make the boats go faster.  But the typical ferry route involves more time at the terminal than underway. And the terminals themselves represent almost as significant an economic investment than the ferries they serve. It is an examination of the potential to utilize driverless vehicles in the terminal-ferry interface is that gives us insight into the transformative potential of this new technology.


Loading walk on passengers is easy - an 8 foot wide gangway gets literally hundreds on board in minutes.  Cars load much more slowly however. When all goes well  the two lanes that feed the open ended ferry will allow it typical ferry to load 200 cars in under 20 minutes (@ 18/min). this rate is largely influenced by the fact that the process must be done at a speed which accommodates drivers of all skill and experience levels. The mix of vehicles is heterogeneous, and there is very little opportunity to organize them during the loading process. Unloading is faster (subject to traffic congestion at the destination), but not significantly so. 

Loading autonomous vehicles would be different in at least three significant ways; 

-The process would be more highly organized with vehicles moving in a highly predictable matter including higher speed and smaller spacing between vehicles. The final load configuration would be more uniform and significantly more efficient. Even without other advantages this would result in at least 25% time savings at the terminal.

-Vehicle loading and unloading could be synchronized. There are (at least) two lanes available and loading and unloading would be simultaneous. Time-saving here could be assumed to be significant as well, perhaps as much as another 25%.

-Passengers loaded directly onto the ferry without use of intervening modes. During the boarding/unloading process vehicles could board the ferry, discharge passengers, and leave the ferry, without significantly affecting turnaround times.

The halving of turnaround times at the terminal would result in at least a 25% reduction in trip times and increase of the number of trips at the ferry could take on a given day by about 25% to 35%. Most importantly the overall system capacity would see corresponding increases. Other potential improvements to ferry system infrastructure deriving from the development of autonomous vehicles include;
Reduced vehicle size and weight associated with driverless cars increase ferry loading.
Just in time arrival of vehicles to the ferry reduce the need for large holding areas.
Greater reliability leads to increased commercial use of ferries

The most significant effect in the long run, however, would derive from the effect of driverless based system on the passenger experience. The average car and transit user would see their overal commute time of well over an hour ( 30 min pre-board, 30 min trip,15 min off-load) decrease by at least 50%. Greatly increased reliability and shorter trips will attract greater numbers of users to the system, reduce the costs per user (or lower existing tax supported subsidies) and lead to an increase in regional economic activity. In short, the marine highway transformed into a Freeway, turning one of the major constraints on regional growth into a catalyst for sustainable development. 

Looking into the future often suggests a return to historical patterns. Before the advent of the automobile and an efficient highway system it was the Puget Sound's "Mosquito Fleet" of steamships that tied the growing towns of the region together. It should not be surprising then that this unique inland waterway will continue to play a significant, even expanded role during this next phase of development. Although it's certainly too early to begin working out the details of how to harness driverless technologies, the time is coming when a preliminary study should be done. System managers might be surprised at what they find. 

Tuesday, October 21, 2014

Urban Transportation; The Shape of Things to Come. Part 2

The streetcar, in addition to its visible charm, was an engine of significant change in urban transportation. Over the space of a few years it enabled a substantial geographic expansion of most American cities and continues to provide the backbone for numerous European municipal transport systems. All this from the simple replacement of horsepower with electricity.  The basic form which electric trolleys built upon was network of horse drawn people movers called omni-buses, and the transition to electric power took less than 5 years in most places.

My family and I recently spent some time riding trolley cars around San Francisco.  I was surprised that what I assumed  a tourist attraction actually a functions as an important part of the Bay Area Municipal transit system. And the smile on my daughters face speaks volumes about the fun it is to ride.
Sustainable Smile!

It got me thinking again about the range of forms public and private transport developed over the past hundred years, and just which of them a driverless world will adopt. In an earlier post I took a look at that broad category of human powered vehicles described as "work bikes" and what attributes they might lend to autonomous vehicles.  Here the focus is on one of the most popular forms mass transit of an earlier age - the streetcar.

 Reliable, non-polluting and solid, both vehicles and track provided a sense of permanence largely missing in a rapidly changing world. Their narrow gauge rails create a footprint that is substantially  narrower than an automobile lane and allow for a long, slim vehicle that is somehow more visually appealing than a bus. And the sound! Cinematic.

But back to my daughter's smile. The cable car in SF is unique in the access it provides and the proximity between rider and traffic . It's too exposed for long trips or harsh weather, but one could imagine a scaled down version operating pretty well in the safe road environment driverless traffic would provide. In any case it's another example of the wide range of  forms driverless vehicles might borrow from, largely because there's reason to expect a greater flexibility in design without the structural requirements inherent in today's vehicles.

The romantic in me hopes that the cable car, having survived the age of automobiles, will flourish in an driverless age.

Thursday, September 25, 2014

Sustainability and the Promise of Driverless Cars

Bottom line. Sustainability is why I'm interested in driverless cars.

And It's why we should all be interested.

We  are, after all, facing existential challenges .  Central to them all is the fact that 5 billion people (give or take) are shortly to join us in the developed world. While a wonderful thing in general, with countless fringe benefits and unseen potentials, it is almost certainly unsustainable with the transportation tools at hand.

And as much as I'd like to sleep at the wheel, or no longer have to look for parking, I wouldn't care about driverless cars if they didn't have the potential to tackle real-world problems.  If this technology doesn't increase our ability to deal with the very real challenges facing us today then I have no  interest in it at all.

Can driverless vehicles, and the driverless system they enable, make a difference? Not just an incremental one, not just a marginal improvement,  but change fundamentally the way we move ourselves, and our things, across the face of the earth?

Here's why I think they can.

To a greater extent than trains, or horses, perhaps more than every form of transportation since walking, every aspect of modern life is accessible to the automobile. Because of this a fundamental change in this one piece of technology has the potential to change society significantly and at every level. and what more fundamental change could be made than to replace the guidance, communication, and control system with the most powerful modern technology, the computer?

One of the things that astonishes me about the conversation centered on driverless cars is how limited is in scope. Especially as this appears to be a potentially significant change to a system which is integral to almost every human endeavor.  The title of this blog was chosen to reflect the narrow scope of the conversation surrounding a technological change in an earlier era, one that saw the internal combustion engine as merely the replacement of one method of propulsion with another, somewhat less reliable one. This is the effect that the replacement of horses with the internal combustion engine had. And hardly is the ink dry on the change this minor adjustment has wrought than another change is upon us.

It is, however, a question that will likely be in the minds of those individuals that attempt to adapt this tool to deal with the very real problems we will face in the coming years. Those that focus exclusively on the technological, legal, and social challenges should not lose sight of the larger goal: a sustainable, perhaps even sustaining, transportation system.

Tuesday, July 22, 2014

The Cost of Driving

The true cost and impact of our modern transportation system is hidden in plain sight, obscured by its sheer size and central role in our daily lives. So entangling is the relationship between society and its means of transport that we often lose sight of the distinction between them. Looking around at our environment, especially if we live in the city, there is little that we can point to that is not largely defined by the needs of the automotive systems. 

The human cost alone of our automobile based system is truly shocking. Worldwide the roads consume lives at the same rate –roughly one million every year -as did the concentration camps of World War II. The wounded number tens of millions more. In addition there are the large numbers of people debilitated by air pollution and associated impacts of the internal combustion engine.  And yet these costs, as vast as they are, are only the tip of the iceberg in terms of the human resources committed to the system. Each one of us is required - on a daily basis - to operate the vehicles that support the infrastructure. Simply put, there is no other single economic activity that requires so much human labor to accomplish.

Environmental impacts are at least as troubling, especially the challenge CO2 emissions may pose for humanity in general, and for developing countries in particular. The entire ecosystem of the planet is put under pressure by the enormous weight of carbon emissions. Wildlife habitat is degraded in direct proportion to the enormous size of our transportation infrastructure. 

One quarter of the developed world’s urban landscape, a third of its energy resources, and countless human lifetimes are spent keeping the system in motion. It is a system so pervasive that it forms a backdrop for most of the dilemmas of the modern word. From the spiraling inflation of urban housing prices to the increasingly fractured urban and suburban landscapes, the car is implicated in much of what is troubling about contemporary American society. Additionally , the enormous demand for fossil fuels is at the root of many today's most challenging geo-political dilemmas. By any measure the financial costs associated our transportation system exceed those of almost any other national endeavor such as health care, defense, or education.

Establishing the true cost of the present system is more than an exercise in accounting. The cost, when fully recognized, creates urgency in our search for solutions and alternatives. If we avoid examining these impacts it is largely because they appear to be the price of living in a modern world dependent on the availability of a flexible and reliable  personal transportation network. 

As viable alternatives develop these costs should be more closely assessed. Both as a reminder of the problems we are trying to solve, and to help avoid repetitions of older patterns. 

Sunday, September 1, 2013

Driving the Future

The First Soccer Mom

Putting children in a car alone and sending them to a destination will be the ultimate test of our confidence in driverless technology, and parents are not known to be first adopters. But mobility is an ever more essential component of child rearing and puts ever greater demands on parents, especially mothers.

Technology will never bring an end to gender issues, but it certainly can add to the confusion. Driving kids around may not approach hand-washing clothes for sheer drudgery (even men will do the driving when asked),  but it is still a job that falls primarily to women. And we shouldn't underestimate the effect this task has on gender equality, and the difficulty it creates for a significant number of parents to hold full time positions or advance a careers.

Even before driverless systems become ubiquitous, safer streets may result in a renaissance of neighborhood children at play. Even a moderately efficient system would result in fewer cars cutting through neighborhoods, and semi-autonomous safety features would diminish pedestrian accidents.

It's  fairly easy to see how such a system would have to function, with driverless vehicles returning kids to their parents if trusted parties are not verifiably at their destination. Safety would have to be absolute, perhaps with child occupied vehicles given privileged right of way and extended safety buffers.

Of course, no reason the parents can't still ride along......

Tuesday, April 2, 2013

The Next Great Turn of the Wheel

Change is coming.  Over the next 25 years driverless vehicles will begin to transform the way we live, work, and organize our urbanizing world. It derives from the revolutionary nature of new tools available to us,  and may provide us with a unique opportunity to re-balance the relationship between nature and technology.

A Revolution, again. The transition to driverless vehicles will have recognizable similarities with past transitions in the ways we move ourselves, and our things, across the surface of the earth. Disruptive, comprehensive, and inexorable it is a process of change that began with walking and will continue to have profound and far-reaching effects.

The combination of pre-existing technologies with more recent innovations are often at the heart of important changes in transportation. In this case one of the most productive technological lineages in human history, the wheel, is being combined with the emerging power of the computer. Not since the replacement of muscle power with mechanical sources has there been such a fundamental shift. For the first time in history the wheel is being provided with an independent guidance system, with a capacity for reliability and efficiency that far exceeds the human capacities.

Hop in, what could go wrong?
This blog will explore some of the processes underlying this change, keep an eye on emerging events, and  discuss possible implications.  This subject will only get increasing attention as the technology develops. But there is a lot more to it than meets the eye, and I hope that by understanding the change and where it comes from we can take advantage of the opportunities ahead of us. As well as avoid some of the pain that inevitably derive from this disruptive transformation.