Regulating something before it even exists is as tricky as it is ill-advised. But that’s exactly what California state Sen. Nancy Skinner, D-Berkeley, wants to do with the nascent self-driving car industry.

Skinner has introduced S.B. 802, legislation that would require any fully or almost fully autonomous vehicles to be certified as “zero emissions”—that is, equipped with fully electric powertrains or hydrogen-fuel cells—to be eligible for registration on California roads.

Of course, fully self-driving cars aren’t yet available on the market. But under Skinner’s bill, any such cars that might someday exist—those categorized as Level 4 or Level 5 autonomous vehicles, using the definitions set out by the Society of Automotive Engineers—would be banned from California if they produce any emissions at all. In other words, she is seeking to ban an entire class of technology before it comes into existence.

Moreover, if Skinner’s bill makes it into law, it could serve to delay deployment of highly automated vehicles throughout the country. California’s unique position as the nation’s largest car market gives it the leverage to shape national trends. As has been seen with tailpipe emissions, whatever California chooses to do will certainly have effects on the national market.

Trickier still, Skinner’s approach probably wouldn’t be preempted by federal vehicle regulation. While the federal government preempts basically all safety-related state vehicle rules, states long have been able to control how they register vehicles to drive on their roads. Were S.B. 802 to become law, there would be no immediate solution from Washington to remedy the problems it would cause.

The central problem is that S.B. 802 would drive up the cost of self-driving vehicles, though it’s hard to project by exactly how much. Based on the projected impact of President Barack Obama’s fuel-economy mandates, which sought simply to make gas-powered vehicles more efficient, it certainly would be expected to run into the thousands of dollars per-vehicle. A wholesale shift to alternative propulsion would no doubt prove even more costly.

By increasing the cost of new vehicles and the new technologies associated with them, this legislation would slow self-driving technology’s pace of adoption. It also would ensure that self-driving vehicles are virtually inaccessible to low-income buyers, thus serving to delay what might very well be the largest safety gains contemplated in the modern transportation era. The human cost of that delay could be staggering, as more than 40,000 people were killed last year on the nation’s roads.

The great irony of these sorts of effects is that they each cut against the very goals Skinner wants to achieve: a cleaner environment; accessibility to marginalized communities; and—though curiously not mentioned in the intent language of S.B. 802—improved safety on California’s roadways.

The stakes associated with controlling vehicle emissions are high. Thankfully, a proliferation of non-gas-powered vehicles already is well underway. But it’s still going to be decades before we see an entire non-gas fleet. If policymakers want to accelerate the day that fleet arrives, they should focus on supply-side incentives to adopt alternative powertrains.

(This post was updated by author with stylistic changes.)