I enjoyed Danny Krebs' article "Personal Transportation in the 21st Century and Beyond" in the October issue of Physics and Society, as a nice review of the status of various alternative fuels for cars and trucks for the next decade or two. However, I was a little disappointed that the article didn't fulfill the promise of the title and outline some of the potential longer-term changes in personal transportation that could make a much more significant difference to the problem.

For example, many people now find much less thrill in driving themselves around than did those of earlier generations; to many it's a waste of time they could spend with their electronic gadgets. This has had a number of effects, particularly on transit ridership – see for example this study from just this year: http://www.apta.com/resources/statistics/Documents/Ridership/2011-q2-ridership-APTA.pdf that showed huge jumps in some cities (like Austin) that have been adding transit services, and generally a steady increase across the US. Can we expect “personal transportation” to decline in favor of public transportation in the 21st century? That would likely require both service increases and land-use changes (suburbs becoming more urban or at least town-centered) over the long term. It would have been nice to see some thoughts on the impact of such changes in Krebs' piece.

Then there are the self-driving cars, which Google has been experimenting with among others: http://www.nytimes.com/2010/10/10/science/10google.html. If people no longer care to drive themselves, which seems increasingly likely for the decades beyond 2020, that opens up a number of opportunities in improving the efficiency of “personal vehicles”, which can then merge into spontaneous groups (cars can be much closer if human reaction times are eliminated) with efficiency approaching that of high-ridership buses or trains.

Electric vehicles also open up another opportunity - to move the fuel off the vehicle altogether. Electric trains pull their power from the tracks they pass over; at least one group in Japan has been experimenting with powering personal vehicles directly from the road in a similar fashion: http://www.smartplanet.com/blog/transportation/electric-roadways-would-allow-plug-in-cars-to-charge-on-the-go/963. The convenience and simplicity of this approach seem highly advantageous - but capital costing and payment mechanisms may make it hard to implement.

I hope Physics and Society will encourage more unconventional ideas of this sort in future articles on transportation solutions.

Arthur Smith (APS Life Member)
Selden, NY

Danny Krebs responds:

I agree with your comments. I was probably guilty of not thinking “out of the box” in the sense that I did not consider the possibility of attracting substantially more ridership to public transportation, or the potential for changing the nature of the highway system itself. My interest in this area grew out of a desire to look at the private automobile from a physics perspective along the lines of questions such as: How much horsepower does it take to cruise at highway speeds?[about 20 HP, assuming 70 mph, 30 mpg, and a 20% efficient engine]. How much peak horsepower is required to accelerate a 3000 pound vehicle zero to60 in 10 seconds? [about 132 HP]. What is gasoline, anyway? [mostly aromatic hydrocarbons]. How real are biofuel solutions? [not very, at this point]. Could methane hydrate deposits be exploited? [probably not]. I had to modify the paper quite a bit when I presented it to the local Torch Club.

In my defense, evolutionary changes are generally cheaper and more readily implemented than revolutionary ones. I am not sure if petroleum dependence a 50 year problem or a 5 year problem, but I am pretty sure that we better start working on solutions.

Danny J. Krebs

These contributions have not been peer-refereed. They represent solely the view(s) of the author(s) and not necessarily the view of APS.