It took me a while to accept the concept of ‘noise pollution’, that noise can be a difficult to control nuisance which can lower the quality of life for those exposed to it. I try walking down Walnut Street Bridge while listening to music and I find myself unable to hear anything other than tire noise as cars accelerate up to 45 mph for all of a quarter of a mile. That noise is waste; it is energy lost. It is miles per gallon converted into decibels. And it adds up. When a particularly full bus or heavy truck passes, the road deck will vibrate. That too is energy lost; that too is diesel acting as vibration rather than propulsion. Down by the Schuylkill, where the old Post Office building is, with 30th St Station just to the north, many paths and means of transportation overlap. The river no longer carries traffic, but the Schuykill Expressway carries some 75,000 cars a day in each direction. Right next to it is the North East Corridor, the busiest stretch of intercity rail in the country. Above all of this is Chestnut Street and Walnut Street, carrying cars, cabs, buses and bikers and pedestrians.
All of that traffic adds up to a lot of noise and a lot of energy. Kinetic energy is expressed as half of mass multiplied by the square of velocity. Incremental increases of speed yields exponentially more energy (and noise). I am not as interested in the noise as I am about all that power, and if there was any way to tap into it.
Comparing Google traffic information over time shows the fairly obvious phenomenon of rush hour, when roads reach their carrying capacity and everything slows down. The number of cars passing through drops, as does the energy each car carries. The graphic above shows a very rough estimate of both the number and the speed of cars throughout a 24 hour period. Cars represent mass, speed represents velocity (direction, an important part of velocity, is dictated by the one way roads), and somewhere in all of these gross approximations is the idea that the amount of energy represented by cars driving past peaks just before and after morning and afternoon rush hour. I also calculated, much more precisely, the train time table and how many trains arrive from and depart to destinations south. This shows how much energy has been used to accelerate trains out of the city and how much returns in the form of trains braking as they arrive at the station. The negative values refer to more trains having left than arrived over the course of the day at a given time. If/when they fit trains and the overhead power lines with regenerative braking, the energy of arriving trains will no longer transfer to the heat and the squeaking noise of disc brakes but will be converted back into electricity and transferred back into the grid.
In terms of ‘tapping into’ these streams of energy, there is a difference between opportunism and energy drain. Siphoning off energy, in this case speed, is only useful if that energy would otherwise end up heating some break pads. Imagine speed bumps that power kinetic sculpture. Maybe a wind chime to drown out all the tire noise.