Fully wireless streetcars feasible soon, but not today
Are wireless streetcar technologies ready for DC to build a fully wire-free system? Not yet, but in a few years, they might be.
A panel of streetcar experts from Houston, Portland, and other cities gave a matter-of-fact, balanced overview of the state of streetcar technology last night at a forum sponsored by DC Surface Transit.
Based on the presentations, it appears that if DC wants an affordable streetcar system that isn't at great risk of breakdowns in extreme weather, it can't build streetcar lines today that don't use overhead wires for most of the length. The hybrid approach using batteries across key gaps can protect key viewsheds.
But wires might not last for that long. Battery and supercapacitor energy storage technology is evolving so quickly that in a few years, technologies will allow longer and longer distances without wires, and one day, complete wire-free operation. DC should move ahead with a wire line on H Street, then a battery and wire hybrid system closer to the monumental core, and continue evaluating systems to one day tear the wires down completely.
Overhead wires are overwhelmingly the most common power system for streetcars around the world. Alternative systems break down into three general categories: Ground-level power, on-board storage, and on-board generation.
Ground-level power includes the conduit systems DC used prior to 1962, the Innorail system in Bordeaux, and experimental systems like the magnetic induction system Primove. The conduit system was the result of a wave of experimentation that happened from 1888 to 1895 when Congress banned overhead wires in the L'Enfant City and also anounced its intention to ban horse-drawn streetcars.
People tried cable cars, a "skate" that connected two distantly separated rails, and even pneumatic systems before settling on the conduit, which had a narrow channel in the road where a "shoe" reached down and connected to the live wires. Paris, London, New York, Bordeaux and other smaller cities used some conduit as well, but it was expensive to install and prone to breakdowns and problems with snow and debris getting in the channel.
It's safe to touch an Innorail third rail. Photo from APTA.
However, this is also expensive and has had maintenance problems. It adds about $130,000 to the cost of each vehicle, and track is 300% more expensive. Bordeaux also has a milder climate than DC. Still, a new system in Dubai (which has no snow at all) will use this system.
Other in-ground systems, like Bombardier's Primove which uses magnetic induction similar to electric toothbrush chargers, are still untested and also likely bring large extra costs. Another problem with in-ground systems is that they force the city to buy all tracks and cars from one vendor, keeping prices high.
A more promising possibility is on-board power storage: batteries, ultracapacitors, flywheels, and other more exotic storage methods. This technology is evolving very rapidly and improving at a speedy clip.
Most new streetcars already use some degree of batteries, including DC's, whose batteries allow about 100 feet of wireless movement, enough for moving around in maintenance facilities. Other vehicles are using batteries to store the energy from braking and to even out the load on the electrical systems through wires.
Savannah already has a 1-mile streetcar that can run without wires at all, but they also have overhead wires as a backup and currently are using the overhead wires. Those cars also don't have air conditioning or heat. For a system that has climate control, ½ mile is about the longest we can reasonably expect cars to travel without wires.
Kawasaki claims its experimental Swimo system will be able to go 10 kilometers on a single charge. That's been going through trials in Sapporo City, Japan, but no city is using this for real yet. There have been some reports of overheating, and the batteries need frequent replacement.
There are many different types of power storage technologies, all with different characteristics around capacity, cycle depth (how far it can be charged and discharged), cycle frequency (how often a unit is charged and discharged), voltage, rates of charge and discharge, shelf life, operating temperature and more.
Ragone chart. Image from APTA.
A "Rangone chart" shows how various systems trade off between energy density (how much energy they store for a given weight) and power density (how fast they can put out that energy). Basically, there's a tradeoff between the two, with fuel cells very powerful but slow, and regular capacitors fast but weak. Double-layer capacitors, also known as super- or ultracapacitors, occupy a large middle ground that shows a lot of promise.
It's very possible that within a few years, on-board storage systems might become good enough to run streetcars for long distances without recharging or only recharging at stations. Right now, however, that's not the case. As Scott Kubly pointed out to me after the meeting, battery technology is especially promising because the far larger auto industry is now working hard to create better power storage and regenerative braking, and they have far more R&D muscle than transit companies.
A big advantage of on-board storage systems compared to ground-level power is that there's no infrastructure in the tracks. Therefore, every time a city buys new cars, they can upgrade to better systems without having to replace all the tracks. They can also run multiple vendors' technologies side by side.
Some cities do use streetcars powered in some areas by diesel generators. These take up some room in the vehicle, emit clouds of pollution, and create noise and vibration, just like buses do. Fuel cells show some promise but are also still not commercially viable yet.
The biggest consideration in a power system is risk. The more untried the system, the more likely it is to break down. Houston's Thomas Hickey talked about BART versus PATCO, two transit systems built at the same time just before Metro. Both used state-of-the-art systems with automatic train operation. BART relied on it, while PATCO planned to use human operation for the first few years. As a result, PATCO was running at 75 mph from the start, while BART had to run at 35mph for 2 years while they dealt with problems that cropped up in the technology.
Therefore, Hickey recommended trying to be the second city to adopt a technology instead of the first, and to always have a backup plan. DC, for example, could build an overhead wire system on H Street and try out new cars that have batteries. For some distances, they could try lowering the pantograph and running on battery. If it fails, they can always put the pantograph back up.
Once that works smoothly and reliably, DC could proceed to operating a line on K Street that omits wires in a few areas, like from Farragut to McPherson Square and around Mount Vernon Square. Greg Baldwin of Zimmer Gunsel Frascal showed a design and video they'd made for the Downtown BID (which they promised to send out soon) showing a streetcar running on the K Street Transitway, dropping the wires in those areas.
Once the technology is ready, DC could start buying even more state-of-the-art battery systems that could run entirely without wires, and try operating those on K Street or other segments that have some wires and some gaps. Eventually, DC could switch entirely to wire-free vehicles and tear down most or all of the overhead wires that they had built.
Summary of streetcar power systems. Image from APTA.
After listening to the presentation, I came away convinced that one day, DC will have a great streetcar system and no wires, just like Committee of 100 advocates wish. However, we don't know exactly how long that will be. Maybe it's 2 years, maybe 20. The question is whether we go ahead with a system in the meantime, giving the technology time to develop and providing a "plan B" testbed for new vehicles that's not completely dependent on wireless technology, or wait what could be a long time.
Given the eagerness of H Street and other areas for streetcars, the opportunity to fund it now, and the availability of federal funds from Obama and LaHood's DOT for streetcars and urban mobility now, the smart path would be to build wires on H Street, wires with gaps in sensitive areas, and work hard toward the day when DC can tear out all the wires and run a clean, pleasant, modern transit system that's also wire-free.
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