The usual explanation is that they want to tax only in-state travel, so they need the location data.

That seems like something that one ought to be allowed to opt out of in favor of an odometer reading; I do something like 99% of my driving in my home state, and would rather just go with an annual odometer reading and maybe slightly overpay on my road taxes than have a tracking device in my car.

Because the goal is as much to collect the location data as it is the tax.

No I think collecting the data is much more the actual goal and the tax is a flimsy pretext.

Because the next logical step is to allow jurisdictions (cities/counties/whatever) charge more tax on their roads.

Oh boy just wait until the ultra wealthy realize they can lobby to have a $50 per mile road tax going into their community to discourage the poors from using their parks/beaches/public areas.

This is more or less the purpose of toll roads.

A dynamic toll can be used to reduce incentive to drive on the road at certain times. It's not feasible to make a 10 mile wide road due to congestion for 2 hours during the day.

Solution? Increase the cost during those 2 hours such that fewer people choose to use the road during those hours. You can give poor people cash and they can decide if it's worth using that road during the times with higher congestion, but the problem of exceeding a road's capacity along with the inability to build infinite lane roads is separate from income/wealth gaps.

Everyone already has to pay in time and frustration to use the roads when it is congested. Slapping a monetary fee on top gives priority to the wealthy. $10/day is a lot more when you make $12/hr. When you consider the flexibility afforded to well compensated white collar workers it becomes even less fair.

The drywaller has every right to sit in stop and go traffic with the investment banker.

Yes, and that’s a distribution of wealth problem. Making both the drywalled and banker sit in traffic doesn't solve it. The banker will take a helicopter. Or leave the office early.

Congested roads have externalities such as the congestion backing up into side streets, rubber banding the congestion along the rest of the road, and extra use of brakepads/fuel energy to stop and go.

Spending time in congestion also adversely affects lower paid people because the cost of their time spent in congestion is implicit. If it was made explicit via tolls, then employers would have to pay better to get them to their workplace at peak congestion times.

I suspect being able to assign infrastructure money to the correct county public works departments is a thing. And even on the more simple sense, your odometer read would let California tax people for miles they drove outside of California.

Not that I support this initiative at all, but your suggestion misses some key issues.

Just because its convenient doesn't mean I want that. I want less tracking. At least let people opt in to reporting their mileage and paying an annual tax instead of even more tracking.

Assuming the tax rate was flat, regardless of the road, usage could be found as it is now, with road sensors and cameras. If they want to have different rates for different roads, then that could make sense.