In the recently released report entitled, "Emissions Associated with Electric Vehicle Charging: Impact of Electricity Generation Mix, Charging Infrastructure Availability, and Vehicle Type" the US DOE, NREL illustrates the carbon neutral status of renewable fuels. Then goes on to compare the overall emissions of compared vehicles.

While the report is focused on showing the emissions benefits of BEVs and PHEVs from clean and dirty electric grids around North America when compared to a conventional gasoline burning vehicle, they also use data that shows the carbon neutrality of electricity produced by bioCNG (biomethane), the renewable, chemically identical substitute of fossil CNG (fossil methane aka shale gas or generically "natural gas", though technically, it is all natural gas).

According to the DOE's AFDC website, BioCNG can be a carbon gain of as much as -117% depending on the feedstock source. Most BioCNG is at a minimum carbon neutral by definition, when best practices are used meaning the production is a closed system and has no fugitive emissions.

From New US DOE, NREL report inadvertently highlights carbon emissions superiority of BioCNG vs Battery Electric and Plug-in Hybrid Electric Vehicles by Brad Couch

Finished just in time for the World Gas Conference (WGC) in Paris 2015, we are very  pleased to present International Gas Union’s first report on Biogas. The report comes in a time when we have  high attention on climate and emissions but also on how to find sustainable energy solution to reduce poverty in the world. Biogas can contribute positively to the solution for both  these challenges. 

The report has been developed under the leadership and co-ordination by our Swedish  Charter member, The Swedish Gas Association.  The report gives a good description of the production process from waste to biogas and how  this helps to reduce the refuse mountain and securing energy supplies without impact on the  environment, and how Sweden as a world leader, distilling biogas for use in vehicles (...)

The extraction of fossil fuels has to be reduced if we are to meet new environmental and  climate targets and prevent the growing greenhouse effect. In contrast to fossil fuels, biogas  is CO2-neutral and renewable. Biogas is also the cleanest form of fuel on the market, and  has the potential to replace a large part of fossil fuel use in Sweden. The bio-manure formed  after decomposition is a high-value and soil-improving fertiliser. The biogas process lets us  reuse society's organic waste, and makes it a resource. A sustainable circle of nutrients and  energy is thus created between city and countryside, between consumers and production. Sweden has already come far with regard to the use of biogas, and is a world leader within distilling biogas for use in vehicles. Investment in biogas plants has been made over a  number of years, including with government subsidies. New plants and technology are  continuously being developed. Nevertheless, demand for biogas continues to outstrip supply. And demand is now growing in Europe, with no less than 12 European countries beginning  to use biogas as a fuel for vehicles. Biogas is undoubtedly the fuel of the future

http://www.igu.org/sites/default/files/node-page-field_file/IGU%20Biogas%20Report%202015.pdf

In the week in which senior industry leaders came together at ADBA’s second UK Biomethane & Gas Vehicle Conference to discuss the sector’s strong growth and limiting factors, the Mayor of London has appeared before the House of Common’s Environmental Audit Committee over concerns that London continues to breach European laws on air pollution after almost five years. Current expectations are that London is not expected to meet the EU standards on nitrogen dioxide pollution until 2030, which is a matter of great concern to Londoners as research commissioned by the Mayor suggests that the city’s pollution levels cost 4,300 lives each year. Conceding that more can be done, Boris Johnson said, “there are great things we could do with low carbon vehicles, with stimulating the market for low carbon vehicles.” In response, ADBA is emphasising the important role that biomethane can play in improving poor air quality in our towns and cities. During the biomethane conference, was reported the potential benefits of using biomethane as including: 80 – 90% reduction in Nox; 95% reduction in particulate emissions; 20-30% reduction in carbon dioxide levels; 78 pence per litre equivalent costs; and a payback period of 12-24 months. Mr Johnson’s solution, however, rests with electric cars at a time when industry regulator, Ofgem, has reported that spare electricity power production capacity could fall to 2% by 2015; dramatically increasing the risk of blackouts. In addition, according to the Gas Vehicle Alliance, electric cars are still responsible for 75gCO2 eq./km in greenhouse emissions compared to just 5gCO2 eq./km for biomethane. With strong growth in the use of road gas, a more targeted approach towards converting London’s biggest polluters -such as HGVs, vans and buses which contribute around 40% of the UK’s vehicle emissions- could significantly reduce associated environmental and health risks.

http://adbioresources.org/2014/09/12/biomethane-londons-answer-to-saving-thousands-of-lives/