I agree you can't, but on critical bridges? Seems an oversight to me.
They can find the money for low emission charging cameras though.
Most CCTV is never used "to prevent" a problem but help sort it out later, and very little CCTV is ever monitored by humans in anything like real time, it's there to provide information and evidence when needed, or things like traffic flow where you don't need to be able to make out different humans, or even cars clearly but just see if the traffic is moving.
For example the "ring of steel" that was the original London CCTV network didn't stop many terrorist attacks on it's own, it flagged up known suspicious vehicles (IIRC it used one of the earliest ANPR systems), and helped the police track down the terrorists after attacks...
So you don't need to have cameras completely covering "critical infrastructure"* where the public have unlimited access as it's pointless, you do have them for example at the entrance and exit because that is useful and practical (you can see who got on, and who didn't get off) and if they can cover parts of the actual span at times that's good.
It's a balance of cost, practicality and usefulness. There is little point fitting a dozen+ cameras** extra cameras on a bridge just to be able to make sure you've got no blind spots
The low emission charge cameras are there to solve an ongoing problem that is really cheap to run, it's entirely automated with barely any human involvement except in appeals and to replace the ones damaged by brain donors. Sure you can potentially check the footage later to track cars, but that's no different to most other cameras.
*I would argue the average bridge is important, but not critical, unlike say a nuclear power plant or the only bridge in and out of somewhere.
**You'd need to be putting them both sides of every lamppost, possibly two sets (high cameras have blind spots below them), or fitting new poles, and what level of redundancy is necessary, are you ok with losing footage in light fog, medium fog, or heavy fog? (or replace fog with rain or snow).