100 Miles per Hour and 32 Miles per Gallon
By John Gilkison and Philip Knox
If there was a vehicle you could buy today which would allow you to travel safely at 100 MPH (161 KM/H) on the interstate highway system while still getting 32 MPG would you buy it? It is the working premise of this blog that many Americans would. In fact, buyers would be willing to pay a reasonable $2,000 to $5,000 premium for such high-speed vehicles. Many would be willing to go through the semi-annual inspections, acquiring the special driver’s license, and attend the high-speed driving school needed to get such a specialized driving license.
High-speed fuel efficient vehicles are possible based upon the known laws of physics, known vehicle body construction techniques, and currently available off-the-shelf-technology. The federal government needs to become actively involved in promoting a high-speed interstate highway project, setting the vehicle specifications so the automobile industry can market such high speed but fuel efficient vehicles, and put the infrastructure in place to create the market pull to make the project work.
Our proposal is based on Honda Research & Development Co., LTD data from a Hiroyuki Ozawa paper published in the Japanese Society of Automotive Engineers JSAE Review (1998) 343-349. In this study we extrapolated from data published on a “Conventional 1996 Honda Accord. The baseline assumptions are using the current interstate highway speed of 75 MPH for a starting point. The projections of fuel consumption needed for given aerodynamic shapes are known and based on proven experimental data collected back to the early 1920’s.
A 1996 Honda Accord is a 5 passenger 4 door medium sized sedan with a curb weight of 2,885 lbs. With a projected frontal area of 21.238 square feet it has coefficient of drag of 0.32. The Honda 2.2 liter 4-cylinder engine is rated at 130 B HP at 5,200 RPM and 144 lb-ft of torque at 4,000 RPM. My wife and I owned a 1995 Honda Accord so we know from personal experience it was capable of delivering 32 MPG (while requiring less than 32 brake horsepower unknown to me at that time) to maintain 75 MPH. This fuel consumption rate will be the stated goal for our 100 MPH fuel efficient interstate highway car.
The specification for our 100 MPH car would allow a brake specific fuel consumption of no worse than the 0.448 lbs of fuel per B HP-hour of the 1996 Honda Accord to be adequate. The engine if of the internal combustion type may have no more than two (2) liters of displacement and the vehicle should be able to return 32 miles per gallon of unleaded fuel at a steady speed of 100 MPH. Society of Automotive Engineers Handbook parameters for standard barometric pressure, temperature, and operating conditions apply. While we would leave it to the manufacturers on how to accomplish this, it could be emphasized that most of the fuel economy performance gains should be obtained from aerodynamic body changes alone.
A 100 MPH vehicle like this with a Coefficient of Drag of approximately 0.125, (CD = 0.125) and minor reduction in frontal area, with gear matching would maintain 31.38 B HP necessary to power the car at the increased speed within the engine’s proper map of performance. We would specify that such vehicles would be at a minimum four passenger and possibly five passenger vehicles. High-speed two seat sports cars would not be eligible for the high speed left lane travel on the interstate because of their inherent passenger mileage inefficiency.
In essence we are turning the whole high-speed vehicle concept on its head by stipulating that currently used horsepower requirements for medium sized passenger automobiles (that are sufficient to travel at 75 MPH with a fuel consumption rate of 32 MPG) are adequate to travel at 100 MPH with the same fuel consumption rate.
The key component is improved aerodynamic body forms which will compensate for the increased rolling resistance this higher speed creates. If diesel engines are used instead of gasoline engines, the requirements for MPG performance should be raised to 35 MPG to compensate for the higher BTU content of diesel fuel per unit of volume. Plug In Electric Hybrid Drive or even Battery Electric Drive Vehicles would be capable of the same performance utilizing such body forms with the same power output.
A side benefit of such a project would be that vehicles capable of 32 MPG fuel efficiency at 100 MPH would be capable of far higher fuel efficiency at lower speeds. Our aerodynamic 100 MPH/32 MPG vehicle would be capable of 58 MPG at 75 MPH, 65 MPG at 65 MPH, and 111 MPG at 55 MPH. While the range of the 17 gallon gas tank would be 544 miles at 100 MPH, it would be extended to 994 miles at 75 MPH, 1,119 miles at 65 MPH, and an astonishing 1,889 miles at 55 MPH (until fuel starvation). The top speed of such a vehicle as envisioned here would be an incredible 177 MPH with the stated power plant.
Step One: The government announces the project and the funding for the [High Speed Interstate Highway Travel Act] giving automakers who desire to sell said vehicles three years to produce their vehicle for market. Mazda has already demonstrated the ability to bring totally new vehicles to market within this time frame.
Step Two: Work would begin on the interstate highway system to create a third left lane intended for this high speed travel immediately. The high speed lanes would be created only on rural interstate highways where the current speed is already 75 MPH. Work would proceed from the most southern locations first, especially in the sunbelt, then working north through time towards more northern latitudes.
Step Three: The federal government would institute federal government driver’s license requirements to be in place by the year previous to the start year to allow car owners to meet the requirements for high speed driving school to pass the test. The school would be similar to the training which police departments, security personnel, and the highway patrol currently use.
Step Four: The infrastructure of central control communications to vehicles traveling in the high speed lanes would be put in place. All safety systems should be in place as the high-speed lanes become operational. The government would also guarantee the automakers of specific government fleet purchases of this class of vehicles to insure initial sales.
Step Five: All vehicles would have a built in transponder which would allow the highway patrol to know if the vehicle in the high speed left lane was legally permitted to be there. Any vehicle traveling in these left high speed lanes that was not specifically designed to get the required 32 MPG and incorporating all the required safety equipment would be cited for speeding regardless of their speed. The ticket would be for doing 100 MPH in a 75 MPH zone. An alcohol blood level found for any driver in a high speed lane greater than 0.02 would constitute a DWI by federal law and would be prosecutable by local authorities regardless of state laws in place for that locality.
Travel times between major cities would be reduced by 25%. For example, travel between Salt Lake City, UT and San Francisco, CA (734 miles) would be reduced from roughly 10 hours to 7 hours and 20 minutes exclusive of stops. Tucson, AZ to San Antonio, TX (868 miles) would be reduced from 11 hours and 45 minutes to 8 hours and 41 minutes. These are significant travel time reductions considering they stem solely from only a 25 MPH increase in speed.
While we admit that there are safety concerns we think they all are manageable given the off- the-shelf technology that is available for use in this new high speed vehicle class application. The improved aerodynamics notwithstanding, there is infrared imaging, radar, laser ranging, acoustics, light amplification, automatic computer vehicle control like traction/braking control, and vehicle design elements such as enhanced crumple zones, double wall fire wall construction, multiple air bag deployment locations, double racing style lap belt for passengers, etc. High speed travel would as a matter of course, should not be allowed in inclement weather, high winds, snow, road icing, etc.
We think that the 91 year old appearance of the aerodynamic shape of this new class of vehicles would be instantly overlooked because of the desire the motoring public would have for higher speed travel on our interstate highways. Interestingly enough the interstates were originally designed for higher speeds like 100 MPH. In short this new high speed vehicle class would create a market pull for these exotic automotive body forms, which just the increased fuel efficiency they yield will not do on its own.
Ironically the federal government would be assisting in breaking the “Tyranny of the Paris Dress Maker annual style changes” that the automobile industry has been in the thrall of since 1923. The government would be bringing fuel efficient design into the market place by specifying fuel efficiency for only a given class of vehicles set up to travel at 100 MPH, the power of the market place and the laws of physics would do the rest.
Post Script: Philip Knox of Sanger, Texas provided all the aerodynamic and brake horsepower fuel information for this blog. While I wrote the blog, Phil is in every sense of the word my collaborator on this project. We both feel that for such a project to succeed it must have a working timeline to be mostly completed inside an eight year time frame or less than two successive presidential administrations. Just like Kennedy’s Apollo Moon landing program was.
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