We've had a couple of engineers as PMs in my Southern EU country (one of them is now the Secretary General of the UN - he started his career as an assistant professor teaching systems theory and telecommunications signals), and I can assure you it's no panacea. Pouring concrete is easy and not by itself synonymous with good governance.

And since you said "any other public policy", I have to say I'd easily trade 50 tunnels and airports for access to Wikipedia.