As you say, ubiquitous self-driving cars will eventually crash the speed trap market. But during the transition there may be some interesting escalations.
Self-driving cars collect MUCH more data on other cars than speed cameras can. That data could be used to flag more (and more minor) infractions for charges. There could be a feedback loop of manufacturers getting subsidies for providing the data and adding more surveillance features for more subsidies. One company's software could make a point of flagging infractions caused by a competitor's bugs or quirks.
And if this happens, there will probably be chaff or shielding countermeasures to keep a self-driving car from noticing your own infractions (perhaps reducing the safety of the self-driving car if it can't 'see' you effectively enough to punish you).
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