Im not pretending to be an expert in city planning but lowering the default limit seems like a good place to start.

People still driving crazy? Advocate for a camera(both replies i got said it was the only way it’s enforced and I agree, and lets not bring a cop with a gun into every speeding violation), or for traffic calming devices(speed bumps, narrowing streets with bollards, etc) . If you make it harder to speed on side streets people are going to go back to the thoroughfares as it should be and enforcing those lower limits elsewhere becomes less of an issue.

I’m just spitballing.