Where Have Your Highway Taxes Gone?

litlle bike rider

and Why Are the Roads so Crowded?


I wondered this one day, as I was planting trees along a suburban side road, watching traffic that ran and ran and never seemed to stop.  Why is a little side road so busy?   And why does the traffic seem so omnipresent when the population has not really increased that much?  I decided that maybe if I looked up the statistics from the US Census Bureau and the US Department of Transportation, comparing changes that have occurred in my lifetime, it might explain why my perception of traffic frenzy is so much larger than the increase of neighbors.


  What I found was a simple problem in math: one event multiplies another: if two people buy 3 apples, someone has sold 2 x 3 = 6 apples.  
 
In my lifetime, the population of the US has almost doubled.  Now if we multiply that by the fact that each of us on average is driving almost 3 times as much, we get the increase in total miles driven displayed by the Light Blue line in the Highway Use graph.  

OK, you are not surprised. But what about the Red line?

If we consider another concept learned in high school, Newton's Laws of Motion,  we discover a hint at why what seems like extra highway dollars are getting ground away to nothing.

In the table below, compare a 
1949Ford with a 2000 Ford Exhibition.  Notice the difference in weight.   The popular newer Ford is 1.28 times heavier.  Since Newton's second law states that force is directly proportional to mass, then the newer vehicle has to be causing 1.28 times as much force on the road.  But that is still not the entire story.  Study the table some more.
graph of pop. vs hwy. use

Vehicle Comparisons and the Energy and Forces they Imply


height
(inches)
width 
(inches)
length  
(inches)
ground clearance
(inches)
weight in Lb. Sq. m. frontal area horse power
1949Ford 63.1 72.8 196.8 7.5 3800 2.61 95
1948 Tucker 60 79 219 7.5 4235 2.68 166
2003 Civic 56.7 67.5 174.6 6 2449 2.21 115
2003 Exhibition 78.4 78.7 205.80 8 4850 3.57 232
               

HxWxL cu ft lb. per cu ft gas mileage HP needed to go
30 mph.
HP needed to go 40 mph HP needed to go 50 mph HP needed to go 70 mph
1949 Ford 523.17 7.26 N/R 5.85 13.25 25 68.07
1948 Tucker 600.73 7.05 18-19 5 11.1 21.1 56.3
2003 Civic 386.71 6.33 32-38 4 8.9 17.1 46.1
2003 Exhibition 734.84 6.60 14-18 7.95 18.05 34.52 92.99

The energy required to move a vehicle is a contest of wind resistance and power.  The resistance due to wind increases with the cube of the speed, and therefore is the major sapper of energy above a relatively low speed.  (Think how fast you can pedal that stationary bike.)  But, when you go faster you get somewhere quicker too (if you don't run out of gas), and so the energy consumed to push air out of the way for a set distance increases "only" with the square of the speed.  That 1949 Ford, as boxy as it was,  pushed around less air than the new Exhibition.

I have used a program called 
PowerCalc (® Machinehead Solutions) to compare the required horsepower to go various speeds for the vehicles listed above.  Now, remember those laws of Newton.  If the engine has to put out more power to move the vehicle faster, the force has to be absorbed by the highway.  And what does that imply?  The answer I get says that the extra resistance of the bigger vehicle and faster speed has to cause exactly that much more wear and tear on the road surface.  Here is the equation of wear and tear on the road:  multiply population x increased driving x bigger vehicle x bigger horsepower x higher speeds =  terrible traffic and potholes that could absorb the defense budget.  Simple Math.  

That red line is not really steep enough, especially when you consider the huge increases in truck traffic, the fact that trucks have gotten bigger, the huge increases in the horsepower for modern trucks, better brakes, tires and transmissions.  All that results in more power to the road,  more wear and tear, and more repair needed to keep the streets maintained.
start of trip

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end trip

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Now here is the kicker:

Look at the comparison of horsepower between the Honda at 50 mph and the Exhibition at 70 mph.  Or do as I did and use the PowerCalc (® Machinehead Solutions) to compare similar changes in size and speed and calculate how much energy it takes to go a set distance.  The energy needed to move the Exhibition 15 miles at 70 mph is at least THREE TIMES the energy used to move the Honda 15 miles at 50 mph (and 100 times the energy a bicycle rider consumes.)  If the people of the United States drove smaller cars, and drove at a slower speed, we could easily save more than half the energy the autos are consuming.  Think: the point is to move people, not scrap metal.  Conservation is not just cuddly sweaters, it is real energy and real resources saved right now.

All these small choices (in so many areas) multiply and multiply.  The implications of those choices will affect people world wide, will use resources, and will affect the world around us.  This is called a geometric growth curve and the certainty implied is that very soon there is no longer enough space and resource for the continued growth.

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