What does the State of California think about the use of Hydrogen as a fuel for vehicles.
http://www.hydrogenhighway.ca.gov/hysafety/hysafety.htm
Hydrogen is an excellent vehicle fuel for many reasons. The U.S. Department of Energy compares hydrogen very favorably to other fuels. Hydrogen is not toxic, poisonous or corrosive. As a result of hydrogen's benign nature, it doesn't harm the environment or public health. If hydrogen were to leak it would disperse into the air almost immediately because it is so light. Contrast that with the effects of oil and gasoline spills, and it's easy to see why hydrogen offers such an exciting future!

California Environmental Protection Agency - Air Resources Board lists hydrogen as a viable alternative fuel for use in motor vehicles as well motor driven equipment.
http://www.arb.ca.gov/msprog/zevprog/factsheets/altfuels_fs.pdf
Alternate Fuel Vehicles
An Alternate Fuel Vehicle (AFV) is a vehicle that can operate on a fuel other than gasoline or petroleum based diesel, such as biologically produced diesel (bio diesel) electricity, ethanol, hydrogen, methanol, natural gas, or propane. Alt Fuel vehicles range in function and size from small passenger cars to large 18-wheeler trucks or transit buses. Off-road products such as forklifts, and agricultural and construction equipment are also available with alt fuel systems.Environmental Benefits AFV’s produce fewer emissions than those powered by gasoline or diesel fuel. Emission reductions of up to 80 percent for pollutants such as carbon monoxide, carbon dioxide, non-methane organic gas, oxides of nitrogen, or particulate matter can be achieved. The amount of emission reductions varies by alt fuel type and pollutant.

California Environmental Engineering (CEE)
"CEE feels that the result of this test verifies that this technology is a viable source for reducing emissions and fuel consumption on large diesel engines."

Governor Schwarzenegger announced on April 20, 2004 his vision for the California Hydrogen Highway Network and signed an Executive Order outlining that vision. The following is part of the preamble for the Executive Order. Or you can click on the following link and read Executive Order S-7-04 in its entirety. Executive Order S-7-04

EXECUTIVE ORDER S-7-04
By the
Governor of the State of California

WHEREAS, hydrogen, a non-carbon energy carrier which can be made from clean renewable energy, is ideally suited to address global, regional and local energy and environmental challenges; and

WHEREAS, the State of California is a world leader in renewable energy production, efficiency and conservation, clean air and emission controls, environmental goals and planning, as well as creating, promoting and commercializing new technologies and industries; and

WHEREAS, hydrogen-powered vehicles and infrastructure can lead to energy independence; offer zero or near-zero smog-forming emissions; reduce health problems due to motor vehicle-related air pollution; reduce water pollution from oil and gasoline leaks; lower global warming pollution; improve fuel economy; quieter and smoother operation; as well as provide economic and workforce benefits to help California meet current and future energy needs; and...

In 2003, President Bush announced a program called the Hydrogen Fuel Initiative (HFI) during his State of the Union Address. This initiative, supported by legislation in the Energy Policy Act of 2005 (EPACT 2005) and the Advanced Energy Initiative of 2006, aims to develop hydrogen, fuel cell and infrastructure technologies to make fuel-cell vehicles practical and cost-effective by 2020. The United States has dedicated more than one billion dollars to fuel cell research and development so far.

U.S. Department of Transportation
Do THEY know about hydrogen on demand? You be the judge of that -- here's what they say in their extensive and official publication "Guidelines For The Use Of Hydrogen Fuel In Commercial Trucks, Final Report", November 2007:
"Onboard electrolyzers are used with hydrogen injection systems for diesel engines. In this case, only a small amount of hydrogen and oxygen are produced to supplement, not replace, the diesel fuel used in the engine. The electricity to operate the electrolyzer is typically supplied by the engine's alternator or 12/24-VDC electrical system."

NASA [National Aeronautics and Space Administration, Washington, D.C.]
In their Technical Note Report E-9105 from May 1977, NASA says:
"Adding hydrogen to gasoline significantly increased flame speed and allows for a leaner air-fuel ratio. All emissions levels decreased at these leaner conditions. ...significantly increased flame speed and allows for a leaner air/fuel ratio. All emissions levels decreased at these leaner conditions."

The National Aeronautics and Space Administration (NASA) is a primary user of hydrogen as an energy fuel; it has used hydrogen for years in the space program. Liquid hydrogen fuel lifts the space shuttle into orbit. Hydrogen batteries—called fuel cells—power the shuttle’s electrical systems. The only by-product is pure water, which the crew uses as drinking water.
http://www.eia.doe.gov/kids/energyfacts/sources/IntermediateHydrogen.html

The American Hydrogen Association Test Lab
"Emissions test results indicate that a decrease of toxic emissions". Zero emissions were observed on CO (carbon oxide).

The Society of Automotive Engineers
If you were under the impression that American automotive engineers (Detroit) are unaware of the benefits of hydrogen-on-demand, here's a wake-up pile of evidence; just a few of the many references from their official publications of the last 35 years!!! Proof that they KNOW all about it but say noting to the publWWWc:

Adding hydrogen to gasoline causes significant efficiency improvements due to the extension of the lean operating limit. [Feb.74]
Adding hydrogen showed a potential for very low pollutant emissions with increased energy efficiency. [Feb.81]
HHO produces improvements in engine efficiency and emissions, due to accelerated combustion. [Feb.96]
Hydrogen can reduce exhaust emissions and increase efficiency. A large reduction in nitrogen oxide emissions can be achieved without a catalytic converter due to very lean operation under certain conditions. [June.2000]
Hydrogen increases the flame speed at all gasoline air/fuel ratios, so engine operation at very lean mixtures is possible. [July.02]
Hydrogen extended the lean limit of engine operation, resulting in greater efficiency and reduced emissions, both hydrocarbons and nitrogen oxides. [Mar.03]
Hydrogen reduced knock due to accelerated fuel burn and shortened combustion period. [June.04]
Hydrogen produces lower emissions due to increased flame speed and resultant accelerated fuel burn. [Apr.05]

Sources listed here are not comprehensive.
Sources: Energy Information Administration, The Impact of Increased Use of Hydrogen on Petroleum Consumption and Carbon Dioxide Emissions, August 2008.
Energy Information Administration, Alternatives to Traditional Transportation Fuels 2006, May 2008.
The National Energy Education Development Project, Intermediate Energy Infobook, 2005.
Energy Policy Act of 2005 (EPACT 2005) and the Advanced Energy Initiative of 2006
http://www.hydrogenhighway.ca.gov/hysafety/hysafety.htm