http://letsgola.wordpress.com/2014/07/28/congestion-pricing-questions/
July 28, 2014
Congestion pricing for freeway capacity
is a hot topic. The basic implementation of price-managed lanes known as
high-occupancy toll (HOT) lanes has been rolled out in many cities,
including the new lanes on the Capitol Beltway in Virginia and the
retrofit of existing HOV lanes on the 110 and the 10. These lanes
operate on a simple principle: when traffic increases in the lane,
prices (tolls) are increased to decrease the number of people using the
lane and prevent congestion.
Beyond that, though, a wide range of people have called for congestion pricing on all lanes
of freeways. This ranges from libertarians who favor user fees, like
Randal O’Toole, to urbanists that want to decrease the amount of driving
by increasing costs, to cities and states that see potential revenues.
Theoretically, it is easy to extend the
concept of HOT lanes to the entire freeway. However, it seems to me that
to do so, you have to make a major simplifying assumption about your
freeway network – that there are no capacity mismatches. What does that
mean? It’s probably easiest to show by way of a few examples. Note that
traffic jams on freeways do not necessarily indicate there’s a problem
on the road at that location; rather, they are often acting as a queue
of cars, pointing towards a downstream bottleneck. There are also
questions for long distance trips.
The Off-Ramp Strangler: The 10 at Cloverfield
On weekday mornings, the 10 westbound into Santa Monica backs up starting at the Cloverfield/26th off-ramp. There’s a lot of employment in the area around the future Olympic/26th
Expo Line station, and the local streets can’t handle the traffic
volumes at peak times. The off-ramp acts as storage for cars waiting to
distribute themselves on the local street network, and when the off-ramp
gets full, cars start queuing up on the mainline of the freeway.
If you’re managing an HOT lane, it’s
pretty easy to keep that lane flowing at a reasonable speed. You’d just
charge a higher toll for the lane up to Cloverfield, and then a lower
toll beyond that. The general purpose lanes act as a spillway, soaking
up whatever traffic comes out of the HOT lane.
What would happen in practice if the
whole freeway was tolled? Some people will try to change their travel
patterns by leaving earlier or later, which is the real intent of
congestion pricing. However, some people will just hop out onto the free
local street network. If you charge an arm and a leg to get from Bundy
to Cloverfield, maybe I decide to get off at National, Overland, or
Bundy. That moves the queue of cars trying to get to office parks in
Santa Monica off of the freeway and onto the arterial grid.
Disastrous Lane Drop: The 5 at Norwalk Narrows
Everyone in LA has probably experienced
this at some point: you’re cruising north on the 5 in Orange County,
enjoying some of the world’s finest freeway engineering, and then boom!
You pass the 91 and you slam (figuratively, we hope) into gridlock on
the three-lane section of the 5 through Santa Fe Springs and Norwalk.
This is one of the last unreconstructed 1950s-era freeways in LA. It’s
being widened as we speak, but it’s a great example of a capacity
mismatch between adjacent sections of a freeway mainline.
If you’ve got a managed HOT lane here
(and the Orange County section is clearly designed for that
possibility), you can keep it flowing by charging a punitive toll
through the Norwalk Narrows. If the entire freeway is tolled, you’d have
to charge very high tolls to keep things moving on the three-lane
section – so high, that you might not be able to charge anything on the
five-lane section to the south. That results in a very cheap section
leading into a very expensive section.
Again, the incentive is going to be for
people to use the cheap section of the freeway, and then bail out onto
the free local arterial grid.
Alternatives with Issues: The 405 vs North-South Arterials
This one isn’t quite so much about a
freeway capacity mismatch as it is about the amount of existing
congestion on local arterials.
Northbound congestion on the 405 has
several causes. For one, the prolonged steep grade approaching Sepulveda
Pass degrades vehicle performance, resulting in some vehicles slowing
down. At the top of the pass, you have an intense weaving section
leading up to the busiest interchange in the country, the 405 and the
101. Further upstream, you simply have a lot of traffic from Westside
employment centers entering the freeway between the 10 and Wilshire to
head home to the Valley.
Contrary to popular conceptions of LA,
the north-south arterials on the Westside are significantly
underpowered. Sepulveda is the only true through arterial between
Lincoln and Robertson; the rest – Bundy-Centinella, Sawtelle,
Barrington-McLaughlin, Westwood-Overland, Beverly-Beverwil-Castle
Heights – are Frankenroads, incomplete, cobbled together from various
parts, and not even two lanes in each direction. This contributes to a
major lack of north-south mobility on the Westside.
If the 405 were tolled to maintain higher
speeds, some traffic would shift to this free ragtag network of
north-south arterials. Again, this might be an undesired side effect of
tolling all freeway capacity.
Long-Distance Trips
Existing HOT lanes, like the express
lanes on the 110 and the 10, are managed dynamically: prices are
adjusted to respond to real-time traffic conditions. If the lane starts
to get congested, prices are increased to reduce the number of drivers
that decide to enter. Pricing information is conveyed to drivers using
variable message signs. If you’re already in the lane, the price you saw
when you entered is honored for your destination.
This works well for a managed HOT lane in
isolation; no one knows what the toll will be when they enter the
freeway, so the general purpose lanes just soak up whatever traffic
doesn’t want to use the HOT lane. With a network of HOT lanes, this will
still work pretty well. The number of destinations you can reasonably
indicate on a VMS sign is limited, but you’d always have the option to
leave when you reach the next tolling section. Let’s say you’re in the
HOT lane on the 10 east and you hop on the 5 south to go visit the
mouse, and you don’t like the prices. No problem, you just take the free
lanes.
If the entire freeway is dynamically
tolled, this starts to fall apart. What do I do if I get on a freeway
and I’m not willing to pay the going price? For short trips, you could
check before you leave, but for long trips, it would be an issue. If you
get on the 101 in Woodland Hills and you’re going to Anaheim, what
happens if you get on the 5 and the toll is more than you’re willing to
pay? Do you take arterials? Do you just get off and park somewhere,
waiting for prices to go down?
Private Parts
Now, you may have been chomping at the
bit as you read this post, thinking that there are technological
solutions to these problems: use congestion pricing on the arterials as
well as the freeways, and quote people a price for their entire trip
before they start it.
Those ideas are certainly theoretically possible. However, they may prove politically impossible, for some very good reasons.
Tolling arterial capacity, using existing
electronic tolling methods, would prove unreasonably costly. It would
more or less require turning every traffic light into a tolling
location. It would require trying to communicate toll rates on a block
by block basis. Both of these would be impractical. You could do it
without any roadside equipment by requiring every vehicle to be equipped
with GPS, and having the vehicle’s on-board equipment report the GPS
data to a central facility for calculation of tolls.
Getting a price quote for a trip before
you take it is something we’re all familiar with for things like flying,
ferries, tours, and so on. In the case of flying, the details of your
travel are reported to the government in advance. However, flying is
something most people do rarely. Requiring advance requests for auto
travel fees would bring that level of oversight into people’s everyday
lives.
To be blunt, I don’t think many people
would be comfortable with having to tell the government where they’re
going before they leave, and I don’t think many people want their
movements being tracked by GPS. If you don’t like the NSA recording your
phone calls and reading your emails, you should be worried about the
prospect of having the government follow your whereabouts. While this
would obviously still leave walking, biking, and transit as options for
anonymous travel, it would be an imposition on people’s right to freedom
of movement.
Conclusion
This isn’t to say we should give up on
the idea of tolling highway capacity. I would be curious to see research
on detailed modeling of a real road network (freeways and arterials)
under these scenarios. For example, what would happen on the Westside if
the 405 and the 10 were dynamically tolled but the arterials were still
free? Regarding privacy, would people be more comfortable if the
advance price was obtained through a third-party intermediary (such a
car-sharing service) that could make the reservation with the system in
the corporation’s name?
In the meantime, a more realistic option
than real-time dynamic pricing might be managing freeway capacity the
way that street parking is managed in downtown LA. In that model,
utilization of street parking is monitored, and then prices at different
times of day are adjusted up or down to try to optimize utilization.
For freeways, a schedule of prices could be published and updated every
month, so that users would be able to determine prices before they
leave. For example, say that in August 2014 it costs $0.25 to go from
La Cienega to Robertson on the 10 on weekdays at 12:30pm, and the level
of congestion is still too high. The rate for September would be
increased to $0.30 or $0.35.
In the case of capacity mismatches, it
might be desirable to deliberately underprice freeway capacity so that
the amount of traffic diverted to arterials isn’t too large. Many people
would rather have a queue of cars on the freeway, leaving arterials a
little less congested and available for things like local trips and
emergency vehicles.
Congestion pricing has great potential to
improve mobility in urban regions. But the devil’s in the details, and
we don’t have them worked out just yet.
