The diesel engine is well known for its ruggedness and economy of operation. Diesel buses became a mainstay in the transit industry during the last century as a result of these characteristics. They have their forte in intercity services and on express routes where their engines can operate at relatively constant speeds, or in suburban services running at lesser frequencies where their noise does not pose a problem. They can be effective tools in reducing the greenhouse gas emissions associated with global warming if enough automobile drivers can be persuaded to leave their cars at home and take the bus.
But...
Diesel exhaust is a complex mixture of some 450 compounds, over 40 of which have been identified as toxic air contaminants.
Diesel buses in Edmonton dump between 560 and 1,000 tonnes of contaminants into our streets every year for transit users and pedestrians to inhale. Ventilation systems in draw these toxins into automobiles and into residential and office buildings.
It would require enough fresh air to cover the entire City of Edmonton 9 km deep to dilute the monthly nitrogen dioxide emissions from the City's diesel buses to a level where the risks posed to health could be considered minimal. This implies fresh air to start with and proper circulation, two factors which are not necessarily present at street level.
Diesel exhaust is 10 to 100 times more toxic than the exhaust from gasoline powered vehicles.
The California Air Resources Board determined that the exhaust from ONE diesel bus has the smog-producing potential of the emissions from 65 automobiles. A 1999 report from Health Canada states that smog (also known as 'ground-level ozone') has been found to cause adverse health effects at levels far lower than previously thought.
The US Environmental Protection Association has concluded that even low levels of diesel exhaust are likely to pose significant risks of lung cancer and respiratory impairment. The nitrogen oxides and particulates in diesel exhaust have been linked to asthma and other chronic respiratory diseases. Asthma and Chronic Obstructive Pulmonary Disease (COPD) are two of the most common lung diseases affecting Canadians. Health Canada estimated that asthma and COPD were responsible for over 1.3 billion dollars in direct costs and over 3 billion dollars in indirect costs in 1993. The number of people affected by asthma and COPD is growing.
According to the Centre for Science and the Environment, the exhaust from just ONE new diesel vehicle has greater carcinogenic potential than the exhaust from over 24 equivalent gasoline-powered vehicles.
Swedish, German and American studies have found that frequent exposure to diesel fumes on the job may result in increased incidence of lung and other cancers. One study estimated diesel exhaust exposure increased lung cancer rates by as much as 63%. In the United States, reports warn of the potential for class action law suits resulting from on-the-job exposure to diesel fumes.
Every year in the United States, diesel exhaust contributes to an estimated 60,000 premature deaths and over 125,000 new cancer cases. Some researches believe these numbers are underestimated. The World Health Organization attributes over 4.6 million annual deaths worldwide to suspended particulate matter, a plentiful constituent of diesel exhaust. Japanese researchers isolated a chemical in diesel exhaust known as 3-nitrobenzathrone. It is one of the most potent carcinogens discovered to date. They concluded there is no safe level of diesel exhaust exposure.
Noise has disturbing effects on the environment and on community life. Diesel buses are known to generate noise that has some 175 to 300 times more 'sound power' than ambient street noise. By contrast, passing electric buses are indiscernible above average ambient street noise levels.
Electric trolleybuses produce no street-level emissions. They can help reduce the adverse health effects of transportation emissions and their associated costs.