In order to attempt this, you'll need the following tools:

• North Point District. Which is unlocked at the start of the game.
  
• Radar Gun. Which is unlocked at 2 duty stars for Melting Pot.

If your PC can handle a High Traffic Density, consider raising it as it will give more vehicles and this grind won't take as long: https://cdn.discordapp.com/attachments/859610623461425162/868148916858806272/unknown.png

1: Head to this area: https://cdn.discordapp.com/attachments/859610623461425162/868140688510943242/unknown.png
Because i was in Chester District, the boundary was placed there for some reason.

2: You'll want to be facing this direction, towards the one way street. https://cdn.discordapp.com/attachments/859610623461425162/868140956308865115/unknown.png

3: Every vehicle that goes into the one way will be going 25-30 mph into a 15 mph.

• Each shift is 20 minutes long and i believe you get 5 extra minutes before overtime docking happens. This is when you continue to do actions when your shift's over (parking, warrants, ect).
  
• Do note that people crossing the sidewalk can stop vehicles. If this happens, they'll speed up to 15 when entering the one way. Vehicles may also slow down to 15 as they get through the crosswalk.
  
• If there are accidents, tow the smoking vehicles and let the non smoking vehicles go. Remember, Parking, call-outs, accidents, and jaywalking litterbugs aren't the focus if you are grinding for this.

4: You should get your achievement. https://cdn.discordapp.com/attachments/859610623461425162/868140820858019840/unknown.png

Twitch Clip i've created showing steps 2 & 3 in action: https://www.twitch.tv/videos/1095634026