There is a robust, national conversation about police and justice reform. And by decriminalizing marijuana, Philadelphia is getting a glimpse of what that entails.

Last October, Philly became America's largest city to make marijuana possession a civil, rather than a criminal, violation. The result has been a dramatic reduction in arrests.

Take a look at this chart tracking adults arrested for weed from January to March in 2013, 2014 and 2015. They are down more than 70 percent.

For decades, Philly police put anyone caught with anything from a roach up to 30 grams into handcuffs and a holding cell. The city's new decrim policy gives officers the option of issuing a Code Violation Notice: $25 for possession and $100 for smoking in public. The result has meant fewer interactions between cannabis consumers and police.

It's also saving tens of thousands of hours of police time -- and a big chunk of tax dollars. The RAND Corporation this year released a that calculated a single custodial arrest costs $1,266.

Using the RAND numbers, Philly may have already saved more than $1 million under the new policy from January to March this year compared to 2013. RAND estimated that the cost of issuing citations is a mere $20.

The quick decline can be more clearly seen in this next chart showing arrests, month by month, in 2014.

The shift in policy has allowed police to spend more time on other crimes. Cocaine and heroin possession arrests are combined in the same code in the Pennsylvania Uniform Crime Reporting System. The next chart shows that while marijuana arrests have decreased there has been an uptick in arrests for harder drugs.

Jim Kenney, who sponsored the bill while on City Council, has made the decrim effort a big part of his mayoral campaign. That makes a lot of sense. While other candidates talk about possibilities, Kenney has actually done something quite tangible to change the relationship between the community and police on the streets.

But we are not all the way there yet. One of the most compelling reasons that City Council took on pot decriminalization was the disturbing racial disparity specifically in marijuana arrests. Unfortunately, that has not changed.

The next chart shows arrests of black and white residents January to March in 2015 for marijuana. Black residents are still 7 times more likely to be arrested for weed than white residents.

Some are quick to say that this disparity exists because police are heavily patrolling in neighborhoods of color. But that would mean other arrests, especially for other drugs, would have the same disparity. But that is not the case.

The chart below shows that more white people got arrested for cocaine and heroin in Philly so far this year.

Again there is no statistical or procedural reason that can explain the continued brunt of marijuana enforcement on black residents. It highlights part of a bigger problem with urban policing, one that will take more than legalizing marijuana to solve.

Philly420 will have the numbers on the total civil violations issued for marijuana next week.

Chris Goldstein is associate editor of Freedom Leaf magazine and co-chair of PhillyNorml. Contact him at chris@freedomisgreen.com.