I saw a question on social media about "how did our worst idea become our only idea?" in response to car traffic.
Surprisingly,
I know the answer to this, both practically and theoretically. Get
comfortable and see what you think of my traffic manifesto:
Network
theory says that the value of a network grows as a function of the
nodes connected, generally on the order of a square law (the factor is
argued, but not the general statement). This is known as Metcalfe's
Law. We already collectively knew this for millennia, which is why
paths, streets, and roads have grown to connect everything related to
humans, and you hear stuff like "all roads lead to Rome" and such. The
dawn of the telephone age formalized Metcalfe's Law, and the Internet
has provided another data point, and recently Amazon and AirBnB have yet
again. With any "iteration with preferential selection" situation, you
end up with winner-take-all patterns, as more users add push for
destinations to connect, and more destinations push more users to
connect, and more connections expand the network.
As for human
transport, not much differed if all were on foot, or some were on horses
(note that everything that people complained about cars was once said
about horses and carriages, which too often ran over poor kids with
little repercussion). A carriage could go too fast for existing
traffic, but get to more places conveniently, so all would naturally
gravitate to horses if they could. But horses are expensive, so a
secondary feedback loop prevented a horse-traffic takeover.
In
the 1800's, railroads arose for the same reason. A steam train is fast
compared to a horse, and much cheaper for an individual trip/load, so
rail took over for longer-distant connectivity, and with later
electrification streetcars came along also for local travel. Trains and
trams have complex and expensive infrastructure, so it's hard to have
rail as a door-to-door solution, hence ToD and DoT became valid
concepts. Rail did not really compete with streets, other than to
create dangerous at-grade crossing - the networks connect and overlap,
but do not directly compete. Rail did compete with roads between towns,
but generally rural right-of-way land was pretty cheap so dual networks
evolved.
After 1875, a bunch of interesting things happened.
Electrification brought along sewing machines and washing machines for
the home, and completely changed the central power model of factories.
That's and interesting story....but also at the same time came the
bicycle. Most people today do not know that bicycles quietly took over
the world after the Penny Farthing (and its coining of the term "took a
header") gave way to the "safety bicycle". Cycling manufacture around
the world exploded, and paved streets, which were already common in big
European cities, grew in expanse. Bikes were cheap compared to a
horse, and cleaner, and became popular with men going to newly
distributed craft jobs driven by machine electrification and with women
with new spare time due to sewing/washing machines.
This is
where we see "iteration with preferential selection" playing its game --
for every trip, a person could decide what conveyance to use, and for
each purchase, whether to buy a horse, a bike, a new pair of shoes,
etc. Most people did not buy railcars (though some did), and many could
not buy horses (though some did, and complained a LOT about cyclists
taking "their" streets), but they could buy a bike. With each new bike,
another person could easily reach more distant destinations, and with
each new cyclist there was value to have housing and shops a little
further out. At the same time, electric trams/streetcars were invented,
and these too used street space in cities, but were relatively
few in number so the time-space occupancy was small and speeds were
limited to manage risk acceptably. Theory would say that soon enough,
cycling and streetcars should take over, and cities would also expand.
And they did.
So,
in essence, bicycles and streetcars could leverage the same network to
better advantage than previous transmission protocols, and yet coexist,
so the network adapted to match. Nobody notices the history of cycling
now, as bicycles are small and fit pretty well into a world with lots
of people, some horses, and a few carriages. I'm sure they had parking
issues, but this doesn't much show up in the "hard assets" we see as
streets have evolved. Streetcars are still remembered, given the
"streetcar suburb" housing layouts and continued existence of derelict
rails peeking through here and there.
Then along came cars. Cars
offered the same value that horses enjoyed, and the same issues, only
more-so. When there were only a few, they were owned by the wealthy,
and the same issues were handled the same way: "don't get in my way!".
Since as we've seen the network connectivity value is driven by network
size, and that is determined by speed (given a static density), going
fast was desirable. Early on, we had a few fast cars trying to go more
places, and cars competed with bicycles and horses and then streetcars,
but the secondary limit of price was still in place. Note that cars
also competed with rail, where connectivity existed between towns.
As
car prices dropped, the iteration and preferential selection mechanism
did its thing, and as we know that for any trip one can choose whether
to walk, bike, ride, or drive, and often the car was (and is) the
fastest solution from A to B, so it gets picked.
But over time,
as car volumes increased, the network itself had to grow, and the
combination of demand for road space and parking plus the growing hazard
to other traffic types first impact street usage, and then the roads,
and finally the city layouts themselves. As with bikes and streetcars,
higher speeds enable cities to grow at the edges, but the desire for
connectivity is insatiable (Metcalfe's Law is even bigger than linear,
remember!), so speeds must tend to go up as well. Unfortunately, the
demand for speed and space presses back on the structure of cities,
which responded by becoming less dense (since costs are lower at the
edges) and more car-centric, as increasingly each trip choice would
favor the car. Where streetcar suburbs tend to be dense and close-in,
car suburbs tend to be sprawling and thus further out.
What
limits car traffic? We have seen that this is actually known, with the
Downs-Thomson Paradox -- it grows until another mode of connectivity is
faster. This is precisely what the "iteration with preferential
selection" networking model would say -- if another mode works better,
it'll get picked. But now we know that cars, bikes, and peds (and rail)
do not really share the same network without friction. Cars took over
streets completely, so to use another mode a new network has to be
built, and this requires explicit decisions that are NOT part of the
daily iterative selection and preference process.
There is
absolutely nothing new about this, as transit planners have been saying
for a long time that headway frequency is critical, and yet the
destination coverage is critical too. The square law of network theory
says that transit will be pulled toward covering more destinations, but
the preferential selection per trip says that transit will only be used
when it is the fastest choice.
This also means that on-street buses, as in Tulsa, will never successfully compete with cars.
It is theoretically and practically impossible....the only point
favoring on-street buses is cost, and even that requires public
support. The only people who will use such buses are people who do not
have cars, and that makes sense as a choice for them ONLY IF the cost is
lower, AND their destinations are reachable by bus, AND the time is not
too long. For others, a bus might make sense if a lethargic bus
connection is a small inconvenience on the end of a faster trip using
another mode. So, if you have a fast train into town and then a slow
bus, you might still see the combination as better than a slow drive
with parking hassles and expense.
So, what does this say:
- Alternative
choices about transit architecture can NEVER be made by auto interests,
including drivers themselves. Once you have paid for a car, the
incremental cost per trip is small, and it will self-justify the auto --
it's a stable and durable state.
- On-street
options, like ordinary buses, will not be acceptable trip options UNLESS
they are prioritized over other traffic. Buses are impacted by the
same delays as cars, yet with fewer destinations available and more
stops to slow them. BRT will only attract drivers if given dedicated
lanes and priority.
- Parking is part of the problem
in that convenient, free parking favors cars in multiple ways. If
parking costs more, autos are less affordable as a per-trip option. If
parking is hard to find, it adds to the effective trip time, and impacts
the trip choice trade-off IF other options are available.
- If
all traffic is by car and bus, car traffic will tend to increase until
the travel cost (time and money) exceeds the trip value, unless there is
a point where another mode makes sense. In some cities without transit
this happens when walking is faster than traffic-jammed streets, yet
even for this situation cars hold an edge by making walking physically
hazardous, noxious, and long due to sprawl. Without options besides cars, the network will favor cars and
nothing else, not even human life in general. You'll be able to go
anywhere in theory, but most trips won't be worth the time and hassle,
and crashes and pollution will continue to be major issues for humanity.
- Thus,
separate network infrastructure is critical to enable reasonable
choices along with decent living. With convenient options for transit
and cycling, or even walking, cities can be denser and more connected,
AND car travel will work better too. Oddball trip connections can still
be made by car, while most routine trips can more easily and
effectively be done using another mode. Metcalfe's Law and the
Downs-Thomson Paradox will work together to expand useful connectivity,
while our explicit choices about transit network investments will reign
in the most undesirable aspects of each option.