International Energy Agency (IEA) this month will release a new study, "Bus Systems for the Future," recommending a more rational approach to urban transport and emissions reduction. Clean-diesel gets a high rating.

Rather than pushing high-cost, knee-jerk schemes such as compressed natural gas (CNG) buses or high-cost Metro subways as the supposedly "green" universal solution to urban transport problems, IEA's exhaustive study instead finds that cities should take a more cost-effective "technology ladder" approach to solving clean urban transport problems.

The study (see: www.iea.org, due to be available mid-August) takes note of the side-by-side cost comparisons done by big transit agencies with lots of real-world experience, such as Los Angeles, New York and Paris. These agencies all find that clean-diesel is far more cost-effective than CNG.

However, the report notes that transits such as Sacramento claimed CNG operating costs can be as good or better than diesel. (Note: This was a false comparison, as Sacramento compared 18-year-old, out-of warranty diesel buses to brand-new CNG buses).

Major cities -- especially those in emerging economies" -- usually can't afford high-cost schemes such as alternative fuels or Metro systems, the IEA study recognizes. One exception could be Dhaka, Bangladesh, which has abundant natural gas reserves, a shortage of oil, and a still-primitive public bus system that potentially could be converted (at least partially) at relatively low cost to CNG, the study suggests.

(Note that the study didn't mention that Bangladesh, like India, might find that importing ultra-low sulfur diesel (ULSD) might be even more cost-effective. That's because of the huge costs of CNG refueling infrastructure, special CNG vehicles, and the inherently poor range of CNG. Natural gas, a low-energy-density fuel, typically can be more profitably suited to "clean" electricity generation, industrial uses, cooking fuel, and, in Bangladesh's case, potential export earnings.)

Well-planned "bus rapid transit" (BRT) systems such as those in Bogota (Colombia), Curitiba (Brazil) and a few other major cities show that many people can enjoy much better transport, reasonable cost, better efficiency, less traffic congestion, and lower emissions, the study shows. Dedicated BRT lanes and reliable, speedy, frequent bus service are critical to making BRT successful, the report shows.

The IEA study recounts the transit experience of many of the world's major cities in recent decades, along with the related urban sprawl, congestion and pollution problems. It also features a series of major-city case studies showing various alternatives, costs and cost-effectiveness.

Using side-by-side cost comparisons of various alternatives proposed to solve these problems, the study shows that most major cities would get far better results per dollar spent by investing first in lower-cost technologies, then consider higher-cost systems, in a logical progression.

The ladder rungs:

#1 Basic bus maintenance: Cities with old, poorly-maintained, black-smoke-belching buses and chaotic, unpredictable service must take strong measures. Government-administered bus route licenses could be imposed, then revoked for poor service and high emissions. Administered fare schemes could reward rather than penalize bus operators investing in cleaner engines and fuels. Or, "premium" buses could compete with "regular" transit by offering faster service and new, cleaner technology at a competitive price (as is now starting to occur in Dhaka). Lower-sulfur diesel fuel (less than 1,000 ppm sulfur) and oxidation catalysts "could be added to many existing buses to reduce CO [carbon monoxide] and HC [hydrocarbon) emissions, and to a lesser extent, PM [particulate matter] emissions," the study says.

#2 Cleaner Buses: Switching-up to Euro-1 or Euro-2 emissions level buses "built in the countries that will use them may be a lower-cost alternative and help develop the vehicle manufacturing industries in each country," the study notes.

#3 Cleaner Diesel Fuels: "Ultra-low sulfur diesel, or even blends of standard diesel with 10% water [emulsions], can reduce bus emissions substantially," it notes. "Combined with advanced emissions control systems that require low-sulfur fuels, these systems can result in diesel buses with emissions comparable to most alternative fuels and relatively low vehicle cost."

Citing a study by India's Tata Energy Research Institute (TERI), the report notes that clean-diesel buses using ULSD would be considerably cheaper to run than the CNG buses being mandated by India's Supreme Court. Aside from the incredible inconvenience of waiting 8, 10 or 12 hours in refueling queues at CNG stations in Delhi is the higher cost of CNG buses themselves. The TERI study shows that a ULSD bus -- even with ULSD fuel imported from Singapore, and not counting the higher incremental cost of CNG buses -- would cost only U.S. 6 cents/mile to operate versus 9 cents/mile for CNG.

#4 Alternative fuels: CNG, LP-Gas and DME (dimethyl ether) work best in buses "that are designed to run on these fuels rather than converted from diesel," the study notes. "The viability of different fuels in different cities would depend in part on fuel availability and fuel supply infrastructure. Installation of refueling infrastructure can be difficult and costly."

#5 Hybrid-electric: While just as "clean" as alternative fuels, diesel-electric hybrid costs "may be out of reach for many cities for years to come," although New York City is buying hundreds of such buses as part of its ultra-clean-diesel transit bus fleet, the study notes.

#6 Fuel cells: "This is still a big step," the study notes, as the costs of such buses are much higher than all the alternatives. What's more, no hydrogen refueling infrastructure exists. While the study at one point repeats a claim that CNG supposedly can be a "bridge" to hydrogen, it fails to note that a massive switch to hydrogen not only would cost billions (even trillions) of dollars, it also burns the CNG bridge by stranding already very costly investment in existing CNG vehicles and CNG refueling infrastructure.

In contrast, liquid-fuels reforming for hydrogen (such as diesel or gasoline reforming) is completely transparent to the existing fuels infrastructure with no stranded investment in any vehicles, stations, pipelines, terminals or refineries, as refiners point out. This ultimately could save consumers -- and entire economies -- trillions of precious investment dollars, while avoiding all-at-once switchovers to potentially problematic, high-cost hydrogen fuel cells.

Other report highlights:

* Bus emissions on a per-passenger-kilometer basis are usually lower than the car emissions replaced by bus transport. "Even 'dirty' buses emit far less pollution and [CO.sub.2] emissions per passenger-kilometer than most other types of vehicles," the study notes. "If [a bus] is reasonably full it can displace anywhere from five to 50 other motorized vehicles, including often very dirty [two-stroke] two-wheelers as well as cars. In some developing cities the primary displacement is of high-emission motorcycles and scooters."

* Some cities unfortunately may be so "spread out" that BRT won't have a very high impact, or won't be optimal. Los Angeles might be the world's best example of a low-density city built for cars. Trying to retrofit BRT looks exceptionally difficult there.

* Smart urban planning tied to BRT development (Curitiba being the outstanding example) could be an excellent model for "developing" cities. Puffing the dedicated BRT lanes in the middle of the highway (as with Bogota's new and very successful "TransMilenio" system) with elevated walkways and ramps for connecting passengers also avoids the "right-turn problem" for all other vehicles crossing dedicated BRT lanes at intersections. Intersection flyovers/underpasses for BRT can solve left-turns.

* Boosting the average number of passengers per bus can pay for clean technology. If faster, cleaner, convenient "BRT" service is offered as an alternative to traffic jams and stress, then more people will choose the bus, thus paying for the incremental costs of cleaner technology. Articulated buses carrying over 100 people are very popular in efficient, customer-friendly, high-frequency transit systems such as Bogota's TransMilenio, the study shows. Bonus: Such BRT systems can be built for a tiny fraction of the cost of Metro subways, CNG or grade-level "light rail."

Notably, Bogota's "TransMilenio" buses (Euro-2 emissions limits, with oxidation catalysts) run on diesel fuel of up to l,000-ppm sulfur. Depending upon future availability of ULSD fuel in Colombia, TransMilenio might eventually convert its system to ultra-low sulfur diesel (ULSD) combined with diesel particulate filters (DPFs) and Euro-3 technology, a TransMilenio spokesman told us.

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