It's a good idea, but they can't have their cake and eat it too. If it's so good for society that they get taxpayer money, the data should be freely licensed. Conversely, if they expect to monetize the data, then we should charge them a very stiff fee for having the monopoly on postal-van cameras (I find it unlikely the postal service would agree to let multiple companies mount equipment on their vehicles, if they'd even let one).