This is our third blog on the Maxi Taxi concept, for earlier blogs on Maxi Taxi go to:

Containerizing People Transportation (Maxi Taxi 1)

What Needs to be Standardized? (Maxi Taxi 2)


The Maxi Taxi concept has chosen five feet as the working standardization width for the system, which would result in road lane widths of about 6 feet. This is a nice return to more traditional road widths, noting that the narrowest roman roads were 5 ½ feet wide (and double lanes were about 13 ½ feet wide).

It is possible that the arbitrary width of five feet is not the exact optimal width, but chances are it is pretty close for quite a number of reasons.


Five feet is a pretty normal width for passenger cars, even though we can choose to design and built passenger cars with widths between less than 2 feet (when thinking in terms of motorcycles) up to 8 feet and possibly a little more. Today cars are generally wider than five feet, for quite a number of reasons, many of which are esthetic. While it is fun to design attractive cars, the Maxi Taxi concept aims for maximum utility and efficiency for transportation although, hopefully, the end result will have some level of attractiveness. 


When considering efficiencies, it pays to make the Maxi Taxis as narrow as possible. The primary reason is that rolling transportation fuel consumption is driven by air drag and mechanical friction considerations. Mechanical friction is not terribly size dependent, but air drag is. Air drag is driven by the system speed, the drag coefficient of the system and the frontal area of the system. As such, reducing air drag by minimizing width (and height) helps the entire system efficiency.


Unfortunately humans are rather large (Let’s face it, why do we have to be this large? Just making people smaller results in tremendous efficiencies.), but based on largest human sizes, in theory, the system would only need to be two feet wide (the width of a motorcycle, and, to make if even more slippery, we could make it only two feet high). That is a rather tight box. Still it is worth considering standardized passenger transportation systems that are only two feet wide. We could snake the system into many places where previously there was no access. As a matter of fact we would be able to run the system right into homes. The question is: Is there a benefit for that? And the answer is maybe, but if we need such a system we could transfer from a wider system to a narrower system. (Maxi taxi to Segway?)


However, for the type of transportation we are talking about, with operating ranges of, let’s say, 2 to 400 miles at 20 to 70 miles per hour, sitting in a two feet wide box would be less than attractive. How small should we go next, and that is where five feet becomes interesting.


Consider the following:


1.    When subtracting optimized wall thicknesses, five feet will allow two humans to sit next to each other comfortably and three humans tightly for a short run.

2.    Most cargo pallets are less than 42 inches on their short side, which would allow loading of those pallets between the wheels of a Maxi Taxi and, as will be seen later, this will be an additional interesting benefit of Maxi Taxi

3.    Modern road widths are in the 11-12 foot range, dividing road widths by two will allow two convoys to move on a single conventional lane if automated driving is used.

4.    New roads will only have to be five feet wide, but can be designed to be 11 feet wide where the extra lane normally functions as parking space unless a wide load by special permit needs to be transported on a particular road segment.

5.    The five feet overall width requires rather thin car wall thicknesses if one tries to fit three humans across, but setting this tight standard will be an incentive for innovative engineering of the Maxi Taxis over time.

6.    Automated driving tends to result in reduced side impacts and this in turn will probably reduce car side wall thicknesses. In other words, while initially 5 feet may not be the most attractive width for Maxi Taxis, over time, it could very well become more optimal.

7.    There is already a wide selection of five foot wide cars available to the consumer.


Image credit Connor Schembor


Furthermore, the rather narrow five foot width introduces a metaphysical restriction that could have very significant efficiency consequences. For example, a five feet width restriction, at first glance, may be a death knell to the RV industry. However, instead, it would result in a much more efficient, vibrant and effective RV industry. This may seem counterintuitive, but will be discussed later. (For a very different take on this see the Solar Conestoga) Anyway the world's coolest RV, the VW microbus, was only 5 foot 7 inches wide.


In continueing to exercise the question of optimal width our highschool intern Connor Schembor has done some more work in this regard, and his work appears to support 5 feet as optimal. This is his discussion of the subject.


Connor also did some review with regard to estimating the increase in passenger carrying capacities that can be achieved. 


Most of the above considerations indicate that if the Maxi Taxi width of five feet is to be accepted as optimal, it would have to take into account the advent of automated driving.


The next Maxi Taxi blog will further discuss automated driving.




Photocredit: Terry Johnson


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