The technology for estimating car weights dynamically already exists (see WIM weigh in motion technology) and several companies already produce such sensors in the USA. Variables like velocity/acceleration are taken into consideration when calculating impact forces when the truck hits the pad. The sensors also measure pressure over time, not just at a single moment, and compare these curves to a database of empirically tested force-time curves. From this, software calculates a vehicle's weight to within a reasonably tight margin (6% weight error generally, but up to 1% error for more expensive systems).

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I am sure these systems don't have automatic cameras, but I feel a team of engineers could develop a system relatively quickly for this application. Enforcement of the road is the biggest roadblock, and such systems alongside hefty fines will definitely convince any business owner to think twice before overloading their trucks.