Public transit agencies continue to choose clean diesel and diesel-electric hybrid buses over other alternatives

New orders of clean diesel and diesel-electric hybrid buses by transit agencies in major communities like San Francisco, Chicago, Detroit and New York during the past year are a strong indication that clean diesel technology is still the all-around best choice for public transportation, according to Allen Schaeffer, the executive director of the Diesel Technology Forum.

“These new, clean diesel powered buses offer the most modern and advanced technology to transit fleets in a much more cost-efficient manner than other fuel sources,” Schaeffer said. “It’s because of the safety, reliability and efficiency now coupled with new environmental performance that makes diesel the predominant power source for public transit, as well as school and intercity bus services nationwide.”

Schaeffer said recent 2014 and 2015 clean diesel bus orders include:

• San Francisco Municipal Transportation Agency: Mayor Edwin M. Lee has announced a contract that includes a firm order for 61 diesel-electric hybrid 60-foot buses and options for up to an additional 363 diesel-electric hybrid 40-foot and 60-foot buses.
• Chicago Transit Authority: CTA has begun introducing 300 new clean diesel 40-foot buses with an option to order an additional 150 diesel buses.
• Detroit Department of Transportation: Mayor Mike Duggan last week unveiled the first of 80 new clean diesel buses in addition to two diesel-electric hybrid buses.
• Southeastern Pennsylvania Transportation Authority: SEPTA has begun introducing 70 new 60-foot diesel-electric hybrid buses in the Philadelphia area with another 115 buses to be delivered in 2015. 
• New Jersey Transit: The board of NJ Transit has voted to spend up to $35.2 million on a fleet of 37 buses with hybrid diesel-electric engines.
• New York City Metropolitan Transportation Authority:New York City announced last summer that it would remove a quarter of its 1,677 hybrids from the city's roads and replace them with clean diesel models. 

New, clean diesel buses haver educed NOx and PM By 98 percent

“The new, clean diesel bus technology of today is the result of an interconnected system of clean fuels, advanced engine design and exhaust or after-treatment technologies working together to reduce emissions to near-zero levels,” Schaeffer said. “New, clean diesel buses have reduced both NOx and particulate matter emissions by 98 percent compared to 1988 buses.

“Fuel savings, as well as hybrid and biofuel capabilities, ensure that clean diesel will be a key part of a sustainable transportation future. The result is that we expect clean diesel to be the technology of choice for the U.S. public transportation fleet for decades and decades to come.”

Clean diesel is comparable to CNG in emissions

Schaeffer noted that an analysis by the Clean Air Task Force compared 2012 CNG bus emissions and 2012 clean diesel buses to model year 2000 diesel bus emissions.

“The results show that new clean diesel technology is very comparable to CNG in emissions,” Schaeffer said. 

2012 clean diesel bus-2012 CNG bus emissions comparison to model year 2000 diesel bus

(Source: Clean Air Task Force - “Clean Diesel versus CNG Buses: Cost, Air Quality, & Climate Impacts”)

Diesel power systems have been undergoing revolutionary technological advancements that have already achieved dramatic reductions in emissions for urban buses and highway engines. Advances in emissions-control systems and ultra-low sulfur diesel fuel (ULSD) are helping clean diesel engines achieve emissions performance equivalent to compressed natural gas (CNG) and other alternatives.

In addition, new technologies are being used to upgrade older diesel engines, which can reduce key pollutants from existing bus fleets by up to 90 percent. Also, a growing number of transit districts are incorporating the use of renewable biodiesel fuels into their diesel bus fleets, further improving their environmental and climate sensibilities.

Diesel buses account for more than 75 percent of the U.S. public transit fleet

Schaeffer noted that the American Public Transportation Association’s (APTA) most recent 2013 data of owned and leased transit fleets showed the share of fuels and engines in the majority of the U.S. public transit bus fleet consisted of:

• 77.71% Diesel Buses
• 19.90% CNG
• 0.96% LNG
• 0.20% Hydrogen
• 0.11% Electric
• 0.10% Gasoline and Electric
• 0.08% Propane

Of the diesel buses currently in the U.S. fleet, Schaeffer said APTA’s data showed that 81 percent were conventional diesels, 12 percent were diesel-electric, and 7 percent operated on biodiesel.