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Buses and coaches are the backbone of public transportation in Latin American cities. Their specific energy demand and pollutant emissions per person transported are much lower than for private vehicles (provided they are utilized to a sufficient degree). This comparison is valid only when a private vehicle is an (economic or other) alternative for a significant percentage of the people choosing transport mode. However, in absolute terms they still contribute significantly to the air pollution problem. Because they tend to be used in the most densely populated urban corridors, their impact on public health can be disproportionate to their numbers. Therefore a transition to cleaner bus systems, in addition to other, non-technological measures, could have a positive impact on local air quality and public health and could also contribute to global climate protection.
It is important to know that newer engine technology only will work as expected if matching fuel quality is used.
All of the approaches listed in this section have different characteristics in terms of energy efficiency, life cycle and tailpipe emissions (see table below). Most have the potential for being better suited than conventional diesel buses with regard to their regional and/or global environmental effects but only if implemented carefully. It is important to note that there are several non-technical factors that affect the environmental impact from public transport buses. The organization of the public transport system, types of structure of ownership for buses, bus line commissions, design of line network, management of bus operations, renewal of the bus fleet and driver education will all affect environmental performance.
Which technology in combination with which fuel type will achieve the greatest overall, or the most desirable specific environmental improvements compared to the use of conventional diesel buses, can only be determined by means of a thorough analysis which takes all the relevant local conditions into consideration. Important factors in this context include:
- The structure of the existing public transportation system
- The availability and prices of conventional and alternative fuels
- Cost implications for the transition to alternative bus propulsion systems.
The choice of which technological option to use, or whether an entirely policy-based approach might be the most cost-effective option, depends on the specific situation. The Info Pool is intended to provide information relevant for such decisions, but it cannot provide the answers.
There are many different arguments for and against the various bus systems described, in comparison to conventional diesel systems, which are brought forward by different experts and stakeholders. In many cases the published opinions and assessments are non-uniform and even contradictory.
The table below provides a first impression of the most important characteristics, in terms of advantages and disadvantages, of the various bus systems in comparison to conventional diesel buses. Buses and fuels are here treated as a single system.
NOTE: This table is not claimed to be exhaustive, as it is not possible to reflect all existing expert opinions - this is intended to be a tentative summary of the general findings consolidated in the individual bus and fuel pages of the Info Pool.
Clean Buses Tabular Overview
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System type
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Main Advantages
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Main Disadvantages
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Advanced diesel bus and low sulfur diesel
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Lower emissions of NOx, PM, CO and HC
- Makes it possible to introduce retrofit systems (with the use of ULSD)
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- Higher capital costs
- Higher fuel costs
- Modification to fueling infrastructure may be required
-Advanced engine technology
– Improved (more expensive) service organizations
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CNG bus and CNG fuel
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- Potential for lower of NOx, PM and CO
- Lower fuel costs
- Uses inherently sulfur-free fuel
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- Higher capital costs
- Less developed fueling infrastructure· Less experience with operation and maintenance
- Lower driving range
- Higher HC emissions (mostly methane)
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LPG bus and LPG fuel
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- Potential for lower of NOx, PM and CO
- Lower fuel costs
- Uses inherently sulfur-free fuel
- Longer engine life
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- Higher capital costs
- Less developed fueling infrastructure·
- Less experience with operation and maintenance
- Lower driving range
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Ethanol bus and ethanol fuel
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- Lower emissions of PM and NOx
- Uses inherently sulfur-free fuel
- Renewable fuel may leads to lower greenhouse gas emissions and independence from oil imports
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- Requires higher volumes of fuel
- Lower technical reliability
- Less experience with operation and maintenance
- Higher capital costs
- Potential problems with fueling infrastructure
- Fuel costs unreliable, dependent on agriculture
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Electric bus
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- Lower life cycle emissions of PM, NOx, CO, HC and greenhouse gases
- Zero tailpipe emissions
- Potential to utilize renewable energy and reduce greenhouse gases
- Higher energy efficiency in stop-start driving
- Recover kinetic energy via regenerative braking
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- Much higher capital costs
- Lower driving range
- Long battery recharge time
- Increased vehicle mass
- Potential problems with emissions from electricity production
- Less experience with operation and maintenance
- Potentially Higher life-cycle SOx emissions
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Hybrid bus
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- Potentially lower fuel consumption and emissions
- Potential to run in local zero emission mode
- Recover kinetic energy via regenerative braking
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- Higher to much higher capital costs
- Increased weight might offsets some or all of the fuel consumption reduction if not engine is downsized.
- Two different systems may necessitate additional maintenance requirements
- Less experience with operation and maintenance
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Fuel cell bus and hydrogen
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- High energy efficiency and potential to use renewable energy can lead to lower life cycle pollutant and greenhouse gas emissions
- Zero emissions at point of use
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- Very high capital and operating costs
- Undeveloped fueling infrastructure· Still in early R&D phase
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Biodiesel
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- Renewable fuel leads to lower greenhouse gas emissions and independence from oil imports
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-Higher fuel production costs, dependent on agriculture
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Again, it is not intended to be exhaustive, but at best to provide a starting point for individual cost assessments. These must be carried out in the light of all factors relevant to the specific situation. Some further information on cost considerations is provided in the individual buses and fuels sections. But for an in-depth analysis, it is essential to consult the literature provided there.
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Category
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Bus Cost
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Other Costs
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Second hand bus in developing countries (or conversions from diesel trucks), seating 25-40
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10-40
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New diesel bus produced by indigenous bus companies in developing countries
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30-75
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New diesel bus produced in developing countries by international bus companies that meets Euro II
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100-150
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Some retraining costs and possibly higher spare parts costs
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Standard OECD Euro II diesel bus*
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180-350
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Diesel with advanced emissions controls
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5-10 more than comparable diesel bus
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CNG, LPG buses
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25-50 more than comparable diesel bus (less in developing countries)
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Fuel infrastructure costs could be up to several million US$ per city
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Hybrid electric buses (on a limited production basis)
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100-150 more than comparable diesel bus (less in DCs)
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Significant costs for retraining, maintenance and spare parts
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Fuel-cell buses (on a limited production basis)
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1 000 (1 million US$) more than comparable diesel buses, even in LDCs at this time
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With up to US$ 5 million per city for refueling infrastructure and other support system costs**
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Source: IEA data (1)* Note that this range of prices includes transit buses in both Europe and North America. Buses in Europe are generally less expensive than in North America, with the prices in Europe for non-articulated buses generally below US$ 275 000.
** Author's note: the cost difference between diesel fuel and hydrogen fuel should also be considered in this context.
New buses sold in Europe today (2003) must comply at least with Euro III regulation. New buses sold in the USA must comply at least with EPA 98 regulation. Vehicles fulfilling these regulations are the most commonly offered on the market. Other developed countries (except Japan) in most cases relate their regulations to either Europe or USA, in some cases with a number of years time lag. Local emission requirements in some city centers can be even more severe than the national requirements for the rest of the respective country. In the developing countries the situation is very different. Some countries have no effective emission requirements nor/or no enforcement.
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The Info Pool also provides expert statements on the comparison between CNG buses and advanced diesel buses, which are arguably the most relevant options under current technological as well as market conditions.
Two articles written by experts on this subject are available within the Info Pool:
"Breathing Clean - Considering the Switch to Natural Gas Buses", by Masami Kojima, The World Bank
"CNG Buses - an Assessment", by Rudolf Petersen, Wuppertal Institute, Germany
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