Last week a marijuana legalization initiative officially qualified for the ballot in Oregon. Voters will also consider legalization measures in Alaska and (probably) the District of Columbia this fall, so by the end of the year three more jurisdictions could join Colorado and Washington in allowing recreational use of cannabis. The differences among the five measures illustrate the advantages of federalism, which allows policy experiments that will help chart the course to the end of marijuana prohibition in America.

Oregon

The Oregon initiative, known as the Control, Regulation, and Taxation of Marijuana and Industrial Hemp Act, combines elements of Colorado's Amendment 64 and Washington's I-502. Like both of those initiatives, it would allow adults 21 and older to purchase and possess up to an ounce of marijuana at a time. Like Amendment 64, it allows nonprofit transfers of up to an ounce. That provision protects people from arrest for sharing pot, which otherwise can be treated as criminal distribution, even if it's limited to passing a joint.

The Oregon measure's decriminalization of marijuana use does not apply to consumption in any "public place," defined as "a place to which the general public has access." By comparison, Colorado prohibits "consumption that is conducted openly and publicly," while Washington forbids consumption "in view of the general public," both of which seem to cover less ground. Like Colorado (and unlike Washington), Oregon's initiative allows home cultivation, but with stricter limits: up to four plants and eight ounces of usable marijuana per household, compared to six plants and whatever amount they produce per adult in Colorado.

The Oregon initiative takes a different approach to taxation than Colorado or Washington, both of which imposed levies based on a percentage of wholesale and retail prices. Oregon's initiative instead would impose taxes on cannabusinesses based on weight: $35 per ounce of buds and $10 per ounce of leaves, plus $5 per immature plant.

One distinct advantage of the Oregon initiative is that it would not change the standard for driving under the influence of intoxicants (DUII, a.k.a. DUID). Under current law, convicting someone of DUII requires showing that he was "affected to a noticeable degree" by marijuana or another controlled substance, based on the "totality of the circumstances." By contrast, Washington's current rule, established by I-502, says any driver whose blood contains five or more nanograms of THC per milliliter is automatically guilty of DUID, a standard that in effect prohibits driving by many daily consumers, including patients who use marijuana as a medicine, even when they are not actually impaired. Amendment 64 did not directly change Colorado's DUID law, but after it passed the state legislature approved a law that created a "rebuttable presumption"of DUID at five nanograms, which in "practice may have the same impact as Washington's law. Oregon's initiative instead instructs the state Liquor Control Commission, which as in Washington would be charged with regulating the newly legal cannabis industry, to study "the influence of marijuana on the ability of a person to drive a vehicle" and advise the legislature on whether changing Oregon's DUII rule is appropriate.

A previous Oregon legalization initiative failed in 2012, when 53 percent of voters said no to Measure 80. A recent Survey USA poll put support for marijuana legalization in Oregon at 51 percent, with 41 percent opposed and 8 percent undecided.

Alaska

Alaska has taken a unique approach to marijuana since 1975, when the Alaska Supreme Court decided that the state constitution's privacy clause allows people to possess small amounts of cannabis at home for personal use without fear of arrest or punishment. But that ruling raised an obvious question: Where are people supposed to get the pot they are allowed to use?

Measure 2, which was originally set to appear on the primary ballot next month but was switched to the November ballot for technical legal reasons, answers that question with a system similar to Colorado's. It would allow adults 21 or older to possess up to an ounce of marijuana at a time, grow up to six plants at home, and transfer up to an ounce at a time to other adults "without remuneration." It authorizes state-licensed growers, cannabis product manufacturers, and retailers, to be regulated by Alaska's Alcoholic Beverage Control Board or a separate agency created by the state legislature.

Alaska's tax would be $50 per ounce, collected from growers. From the government's perspective, the advantage of that approach, which is similar to the way alcohol is taxed (by volume), is that proceeds from a given quantity of marijuana remain the same as prices drop, which is what will happen as the market develops unless something goes terribly wrong. The disadvantage, from a social engineer's perspective, is that a tax based on weight does not take potency into account (unlike alcohol taxes, which fall more heavily on liquor than on beer). In fact, a weight tax might encourage higher potency, especially as it becomes a larger and larger component of the retail price. If production costs fall as expected, Alaska's weight tax could amount to a rate of 100 percent or more within a few years, giving consumers an even bigger incentive to buy the strongest pot they can find.

Measure 2 prohibits marijuana consumption "in public," making it "a violation punishable by a fine of up to $100." The initiative does not define "in public," but that language probably will prevent people from legally consuming marijuana in any setting other than their homes. As in Colorado, the effort to keep cannabis consumption hidden will make enjoying the newly legal product especially problematic for visitors.

Like Oregon's initiative, Alaska's does not change the state's DUID rules. Under current law, blood test results can be used as evidence that someone was driving "while under the influence of" marijuana, but they are not necessarily conclusive. Alaska does not have a "per se" standard like Washington's, which makes drivers automatically guilty of DUID when the amount of THC in their blood exceeds a specified level.

A March poll commissioned by the Alaska House Majority Caucus found that 52 percent of voters favored Measure 2, a few points lower than the support found in a survey by Public Policy Polling the previous month.

District of Columbia

The District of Columbia's marijuana initiative—which has not officially qualified for the ballot yet but probably will soon, since the campaign submitted more than twice the required number of signatures earlier this month—is the least ambitious of this year's three legalization measures, since it does not allow commercial production and sale. Instead Initiative 71 would legalize home cultivation of up to six plants by adults 21 or older, along with possession of up to two ounces and transfer of up to an ounce at a time "without remuneration." Residents who are not horticulturally inclined and do not have friends who are would be out of luck.

Last March a survey by Public Policy Polling found that Initiative 71 was supported by 49 percent of D.C. residents, with 33 percent opposed and 18 percent undecided. By contrast, a 2013 survey by the same organization found that 63 percent of D.C. voters either "strongly" or "somewhat" supported allowing commercial distribution as well as possession and consumption.

Legalizing the marijuana business would require action by the D.C. Council, which probably will not be ready to take that step anytime soon, although it did decriminalize possession of up to an ounce this year, making it a violation punishable by a $25 fine rather than a misdemeanor that can result in arrest and jail time. Even if local legislators were inclined to favor full legalization, they could be overridden by Congress, which has veto authority over D.C. laws. Congress could also block implementation of Initiative 71 if it passes, as it did for years with the medical marijuana initiative that D.C. voters approved in 1998.

Even the decriminalization of possession in D.C. was a step too far for some members of Congress. The House version of an appropriations bill making its way through Congress includes an amendment introduced by Rep. Andy Harris(R-Md.) that bars D.C. from spending money "to enact or carry out any law, rule, or regulation to legalize or otherwise reduce penalties associated with the possession, use, or distribution" of any controlled substance, including marijuana. The impact of the Harris amendment on the new penalty for possession, which took effect last week, is uncertain, since it is not clear in what sense not arresting and prosecuting people for marijuana possession results in an additional expenditure of public funds. But if the amendment is part of the appropriations bill approved by both houses (which looks unlikely, since that would require the assent of Senate Democrats), it could effectively nullify Initiative 71. In fact, the Yes on 71 campaign worries that Harris's rider "could prevent the District of Columbia Board of Elections from using its funds to print the ballots that include Initiative #71."

The White House opposes the Harris amendment, and its rationale is heartening:

The Administration strongly opposes the language in the bill preventing the District from using its own local funds to carry out locally passed marijuana policies, which…undermines the principles of States' rights and of District home rule. Furthermore, the language poses legal challenges to the Metropolitan Police Department's enforcement of all marijuana laws currently in force in the District.

Strictly speaking, "states' rights" do not apply to the District of Columbia. Still, it's encouraging to hear the administration explicitly invoke federalism (as opposed to, say, Justice Department priorities) in the context of marijuana reform. The local autonomy preserved by the Constitution creates leeway for states to give pot peace a chance, and the experience of those that do will guide others in the coming years. In 2016 more states are expected to consider legalization, most likely including California, Arizona, Nevada, Montana, Maine, and Massachusetts.

"Colorado is not going to be the top dog for much longer," says Kayvan Khalatbari, co-owner of Denver Relief, one of the state's best-known dispensaries. "By 2016 we're going to have up to a dozen other states in this country that are legalizing cannabis. I think it's only a matter of time before Colorado really gets overlooked."

This article originally appeared at Forbes.