Until a few years ago, states didn't have the right to raise their own speed limits.

On a recent episode of All Things Legal, Craig Ashton and Ed Schade discussed an upcoming change in Pennsylvania law that will raise the maximum speed limit to 70 miles per hour on some roads in the state. As the All Things Legal team often does, they then expanded on this conversation to look at how the relationship between state and federal law has evolved in recent years—as demonstrated through the federal speed limits and minimum drinking age—with the passage of marijuana legalization initiatives indicating the states’ declining respect for the Constitution’s Supremacy Clause.

For many years, states willingly surrendered the ability to set their own speed limits.

Craig Ashton started off by pointing out that until relatively recently, not a single state in the country had a speed limit higher than 55 miles per hour. This was because the U.S. Congress—in response to the oil shortages of 1973—enacted the National Maximum Speed Law in 1974, which established a nationwide maximum speed limit of 55 miles per hour. While the law was extremely unpopular with both state governments and the residents of those states, the law remained intact until 1987, when the limit was raised to 65 mph on rural non-interstate roads. In 1995, Congress completely abolished the law, allowing states to resume full authority over their roadway laws.

But if the law was so unpopular, why did it manage to remain in place for more than 20 years? Well, money. Any state that ignored the law would likely have their federal transportation funds eliminated. And a few years later, the federal government got the opportunity to prove that it wasn’t bluffing when it came to coercing recalcitrant states to comply with federal law.

In 1984, Congress passed the National Minimum Drinking Age Act of 1984. While it may sound like a hard and fast law that established a nationwide minimum drinking age, its actual effect was much more subtle. What it did was penalize states that allowed people under 21 years of age to purchase and possess alcohol. Any state that flouted the law would have its yearly federal road funding from the Highway Trust Fund reduced by 10 percent. Considering that some states receive billions in road funding from the federal government, a reduction of even 10% would have a devastating effect on their overall budgets. So, while nearly 80% of states had allowed 18 or 19 year olds to purchase as least some types of alcohol in the years before the passage of the NMDAA of 1984, all 50 states quickly got in line, with South Dakota and Wyoming being the last to come into full compliance in 1988.

So, just as money ultimately got states to comply with the national minimum age for buying alcohol, money got the states to lower their speed limits. However, many did their best to defy the law to some degree. For instance, many western states imposed “energy wasting” fines that were issued to drivers who broke the 55 mph speed limit, but didn’t break the state speed limits that had existed before the law went into effect. In fact, in many cases these cut-rate tickets didn’t even result in points on driving records or increased car insurance rates.

As time passed, states starting becoming more brazen in expressing their views on the law. In a 1986 LA Times article, the director of the South Dakota Highway Patrol was quoted as saying, “Why must I have a trooper stationed on an interstate, at 10 in the morning, worried about a guy driving 60 m.p.h. on a system designed to be traveled at 70?” In the same year, Nevada’s state government actually got gutsy enough to raise their speed limit to 70 mph—with the caveat that the limit would be lowered back down to 55 if the Federal Highway Administration got riled up enough to do something about it. As it turned out, the legislative toe in the water turned out to be a wise choice, as the FHA immediately cut all highway funding to the state, triggering the state law’s invalidation clause and automatically lowering the limit back down to 55 mph.

But, as already noted, time and changing views finally led to the elimination of the federal speed limit in 1995, and many states immediately raised their speed limits. And states have continued to alter their speed limits in the years since, with the most recent being Pennsylvania.

Why are states defying the federal government and legalizing marijuana, if they gave up so easily on other issues?

The above raises an interesting question: If the federal government was so successful in keeping states in check when it came to speed limits and drinking ages, why have so many states been legalizing marijuana with little to no federal fallout? Currently, 23 states (and the District of Columbia) have legalized marijuana possession and consumption to some degree or another. And this isn’t just a recent fad: five of those states passed their legalization measures in the 1990s, meaning that the laws have managed to stay on the books through three different presidential administrations. How have these states managed to get away with legalizing a drug that the federal government considers to be as dangerous as heroin and cocaine, and more dangerous than morphine and oxycodone?

The answer is, of course, money. Thus far, the federal government has not acted to cut off any federal funding to pro-pot states. Why this is the case has been the subject of much debate for years now, but in any case, it hasn’t happened yet. And success stories such as Colorado—where the state collected $70 million in marijuana tax revenue in the last fiscal year, dwarfing alcohol revenue of $42 million—make it clear to many states that marijuana legalization is a choice with major financial incentives and few downsides.

This is likely to continue being the case as long as the federal government keeps their pocketbook open, because other options are limited. Due to a constitutional concept known as the anti-commandeering principle, the federal government can’t simply force states to enforce federal laws. This is why the feds instead chose to wield financial incentives to encourage states to play along with the national speed limit and drinking ages. The other option would be for the feds to use DEA agents to enforce federal drug laws in pro-marijuana states, as they have in conducting raids on medical marijuana dispensaries in California and elsewhere. But this would require an extensive expansion in funding. Instead, the Obama Administration has moved to cut DEA funding in recent years, and Congress has acted to tie the department’s hands when it came to enforcing marijuana laws.

So it shouldn’t be surprising that the states are getting more comfortable about stretching—and breaking—the bounds of federal law. As long as the money keeps flowing from the federal government, states will be happy to cash in on the marijuana market. In the near future, states may set their own drug laws as comfortably as they now set their speed limits, even if factions of the federal government continue to voice their displeasure.