I'm going to try to dive in to the multitude of problems this Berkeley proposal will create. For starters, under normal circumstances, a civilian cannot detain someone based on reasonable suspicion. They can only "arrest" on probable cause of an offense committed in their presence. While many on view traffic stops will satisfy probable cause for a violation, there could be big liability issues if the civilian employee was incorrect, or mistaken about the violation occurring. Civilians also have no right to detain people, only to arrest per private person arrest laws. One also has to wonder if they could even lawfully give warnings. Since an stop would only be lawful for an arrest based on probable cause, and in order for that to happen, a citation would have to be issued (better be no mistakes) then I don't see lawful grounds for a detention and release with a warning. They could get around this by changing the law. Certain civilian government, or non-governmental, position have been granted "peace officer powers of arrest" while working. That could be one way. Another way is similar to a law allowing for shop owners, or their representatives, to stop and detain suspected shoplifters in circumstances less than probable cause to make an arrest. So these issues would need those types of law changes.
It is a crime to impersonate a peace officer.
https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=PEN§ionNum=538d But since these would be authorized government employees, with presumably different uniforms not resembling police, this might not be an issue.
Their vehicles would have to be equipped with at least one red light to the front and a siren, per the vehicle code. If the vehicles did not have those things, drivers would not know, nor be required, to yield to them. Since they are not peace officers, the vehicles they used would need a specific approval from the CHP.
http://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=VEH§ionNum=165
Finally, there are no laws requiring someone to stop for a civilian during enforcement situations. 2800 CVC only applies to peace officers.
https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=VEH§ionNum=2800. And same with 2800.1 CVC.
https://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=VEH§ionNum=2800.1
There was a comment in the article by one of their city council persons stating to the effect that civilians employees have successfully issued parking tickets and they liken traffic stops could be done in a similar manner. The problem is, these two things are very different, and operate under entirely different laws. One does not need powers of arrest, a detention, or a red light and siren to enforce parking violations. Parking violations mostly don't involve dealing with people or giving warnings either.
I am sure I am overlooking some additional issues as well. My final thoughts for this post have to do who they might find to fill those positions, and what kind of training they will have. Will they have a pursuit policy? Will they be calling police for help? My thoughts are that training will be minimal. Who would want to take those unarmed enforcement positions? Those who couldn't make it as a police officer? IMO, this has disaster written all over it.
And I also doubt BPD will have a policy prohibiting traffic stops either.