This site’s top image of a tunnel for automobiles may seem to contradict a portrayal of sustainability, but perhaps it is more how imaginatively one interprets the picture’s possibilities.  Who is to say that the green colored tunnel is not actually the hollow stalk of a plant and the automobile within is not a miniature model run on alternative energy or even photosynthesis for that matter.

A tunnel is defined by Webster’s Ninth New Collegiate Dictionary as being ‘a covered passageway; specifically: a horizontal passageway through or under an obstruction’.  Tunnels are built to get from one point to another in the shortest distance possible through mountains ranges, underneath rivers or other impasses.  Factors such as initial environmental impact, geography, engineering, demolition, construction, labor and embedded manufacturing and transport costs all need to be considered.  Inserting a structure into a mountain after blasting may not be as feasible as winding a road around the mountain through its adjacent valleys.  Tunnels under rivers may also not be economically justified as building a bridge that spans from bank to bank.  A large city such as New York incorporates both tunnels such as the Holland, Lincoln and Penn Station railway access as well as bridges such as the George Washington, Brooklyn and Verrazano which are chosen through engineering criteria and urban fabric entry and exit point availability, despite having perhaps less of today’s increasing environmental conscientiousness.

Tunnels also pose another factor of fresh air ventilation and disposal of vehicle exhaust to consider.  Energy must be provided to power the enormous fans that are necessary to blow out the toxic fumes emitted from these vehicles. Although bridges and open highways are not enclosed, utilized fossil fuel exhaust is still not lessened as it disperses into the open air.  This however raises the possibility that tunnel exhaust can be captured, directed through filters, and be re-utilized as renewed energy without further contamination of the atmosphere.  Once all automobiles are powered by cleaner sources of energy without hazardous emissions, ventilation requirements can focus on the provision of fresh air for passengers for the duration of being transported underground.  Ultimately, oxygen could be harnessed from the heavily forested ‘green roof’ of the mountain top above or be extracted from the hydraulic turbulence induced by sluice gated dams and the river‘s tidal currents moving swiftly overhead.