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Well, the more motor traffic capacity you generate, the more congestion you create. I suspect the lack of enforcement, apart from cost, is related to ongoing plans to eventually bring in road user tracking, which would then be used for enforcement. People were much too optimistic about this technology ten years ago and thought it would be in the foreseeable future. However, the technology is not that simple, there are many options as to what exactly to go for, it raises significant surveillance/privacy issues, and now there is the pipedream of automated cars, anyway. Meanwhile, our dependence on far, far too much motorised transportation is still shit and is not being addressed except by the proverbial drops of water on a hot stone.
Other than increasing capacity and monitoring, I haven't really seen that these motorways are all that smart. Even when the speed limits are below the national limit, people routinely ignore them, and cause congestion anyway. I don't see why it wasn't rolled out with more active speed enforcement.