After Colorado jumped on board California's Zero Emissions ship in January, automakers apparently weren't happy.

According to a Reuters report, the Alliance of Automobile Manufacturers, a lobbying group for the auto industry, met with Colorado Governor Jared Polis last month to lobby him to adopt a voluntary EV program instead. Reuters cited a letter it had seen from the Auto Alliance that said automakers would agree to sell all plug-in models that are available in other states in Colorado, would make efforts to promote electric cars in the state, and help buyers take advantage of Colorado's generous $5,000 state tax credit for EVs. (It begins dropping next year.)

Auto Alliance members include General Motors, and Ford, which have each separately said they are converted to an electric-car future, and GM CEO Mary Barra has said on several occasions that the nation's largest automaker plans to transition toward selling nothing but electric cars in the future.

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So far, almost half of all electric cars in the US are sold in California, and it is one of the only states where buyers can choose among all the models that automakers offer.

California recently reported that 8 percent of the cars sold there in 2018 had plugs. The Golden State passed its mandate requiring all new-car makers to sell an increasing number of zero emissions vehicles in 1990. It has since modified the program several times and now requires automakers to sell significant numbers of plug-in (or hydrogen fuel-cell) vehicles there.

The ZEV program is part of California's emissions program, which allows the state to set tighter emissions standards than the rest of the country under the Clean Air Act (because the state's emissions program predated the federal law.)

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As of now, other states have the option to adopt California's emissions law, with or without the zero emissions vehicle mandate, or to follow only federal standards. The EPA's recent plan to freeze federal fuel economy standards would also attack California's current right to set its own emissions standards and work to invalidate its ZEV program. (Colorado has signed on to a lawsuit against the EPA along with 18 other states.)

Today, Connecticut, Maine, Maryland, Massachusetts, New Jersey, New York, Oregon, Rhode Island, and Vermont follow California's ZEV program, Colorado is in line to adopt it, and Washington state looks likely. New Mexico also signed on to the ZEV program in 1993, but later dropped it. In January, New Mexico Governor Michelle Lujon Grisham renewed plans for that state to rejoin California's LEV emissions and ZEV programs as part of a broader effort to cut carbon pollution from the state by 45 percent by 2030.

EV buyers in others states, such as those in the Northeast, often complain that many of the most compelling new plug-in models sold in California are not available everywhere.

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Part of the challenge for automakers is logistics. Cars are big and heavy items to ship. Asian automakers especially, tend to ship their cars to West Coast ports, and incur additional expenses to send them elsewhere in the country. 

Automakers have banded together with East Coast states to market electric cars in states there that have adopted EV mandates. Even then, though, they can ship cars in bulk to a region smaller than California geographically, but denser in population. Selling new plug-in models in models in the middle of the country however, reachable only by rail or truck, in areas without a critical mass of EV buyers, is a bigger challenge. 

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EV advocates are concerned that, even with promises of every model being available, a voluntary program in Colorado could lead to very few electric cars being shipped to Colorado, and possibly only to a small handful of dealers, compared with a mandate.

Arizona does not have a mandate, but has also been a relative hotbed of electric-car activity dating back to the 1990s, when several automakers sold EVs only there and in California. Combined with New Mexico and Colorado, the trio could develop critical mass as a third EV intensive corridor for automakers and boost electric-vehicle availability to the region. Without that, a voluntary program in Colorado would likely result in fewer EV sales there.