You'd likely lose a lot of money trying to do that, you're vastly underestimating the cost of maintaining the data network for that kind of installation alone, even before looking at the cost of physical installation.
It absolutely is a bargain. I don't have the money or time to risk but I strongly recommend that you start a company, build a website and advertise your service to the world. I'm assuming you'll also deal with any regulatory and data protection issues, get permission from local authorities etc... . You've found an astonishing gap in the market, it seems.
Within the UK, 4G sim cards and data are cheap.
Android phone with tether capabilities, Raspberry Pi with solar and a webcam.
Or even better to save all that faff, root a phone, run the drivers plate OCR software using the phones camera, stick to a gantry and send results via text message. You wouldn't even need live updates, pull the latest data at midnight each day.
I suspect the computing and communication parts of a project like this are by far the easiest bits.
Weatherproofing the camera and solar panels, getting permission to get them installed, actually installing them (working at heights over busy roads) and then maintaining them would be pretty expensive. You might also have to pay rent to whoever owns gantries, and what about locations where there aren't any existing gantries?
What about insurance in case you camera falls off the gantry onto a car and kills someone?
Edit: What about roads that don't have network coverage (not that uncommon in the Scottish Highlands)
You wouldn't get permission. Just walk with a phone+solar panel in a weatherproof box. Either use magnets or zip ties to tie to the the pedestrian rail of a bridge overlooking a freeway. Done.
I would likely order some chinaphone motherboards only - for example[1] - without the screen+case+accessories you save ~50% on the retail price. They're then not valuable enough to be worth stealing either.
If it's a small road with no bridges, tie to a lamp post instead.
You need to be able to install 3 per hour to make the finances work out - 10 mins driving, and 10 mins installing, and repeat.
If the city catches you, it's only a littering penalty. They likely wouldn't care.
Anything placed in a location which has easy accessed to pedestrians is going to get stolen and vandalised - particularly once people realise what they are.
How much power do you need to be continuously running video/snapshots, OCR software, and comms? How expensive a solar panel is needed to generate that power, will it work overnight and through the winter, and will it also be theft-resistant? What's the cost of petrol for driving 4+ hours per day? How will you get coverage in parts of the country that aren't near your home/office?
Love the style, but wouldn't those boxes be conspicuous? It only takes a few observant people to notice a couple before they spot the pattern and see them everywhere. Then it seems like the game would be up.
if the city catches you and finds you installing multiple cameras on their infrastructure for private surveillance youre pr0jably going to get charged with all sorte of business violations that will cost you thousandw ler camera plus the citys cost to inspect their infrastruxture.
You'll either have to do this guerrilla style, in which case solar panels will be far too obvious. Or you'll have to apply for all relevant permits, in which case you'll never get them.
Permits? We're not talking a solar farm to power a small device. There are a lot of trail cams that have solar built in, are very small, camouflaged, and motion activated with 20MP cameras for under $200.
We're talking about filming major roads here. "Motion activated" effectively means running 24/7. No way a built in solar panel in a camouflaged trail camera will manage that. Also it doesn't matter how small the device is, if you legally want to attach a camera to any sort of infrastructure overlooking a road, then yes you need permits you almost certainly will not get. You could possibly attach it to a pole on private land next to the road, but even then you'd need the permission of the land owner.