Running late and vastly over budget, a mammoth rail project stands as a monument to what critics say is Germany's glaring failure to tackle long-standing infrastructure woes.

"Stuttgart 21" is envisaged as a major, futuristic rail hub in the southwestern city, a fitting gateway to a region home to the headquarters of corporate heavyweights such as Bosch and Mercedes-Benz.

But 15 years after work began, the project — which involves replacing the current station with a major underground site — is not yet complete.