Reaction to Francis Reynold’s "True Dualmode Cars vs. PRT and Palleted Dualmode Concepts"

by Andreas Steingroever and Rasmus Krevet of Autoshuttle


We regret that Francis Reynold’s article bears many assumptions proved to be erroneous by our work with Autoshuttle. Let’s start with the basic requirements for alternative transportation concepts. Conventional road transportation is very efficient but two disadvantages become prominent in high-traffic corridors through densely settled regions:

environmental friendliness is poor due to the relatively high energy consumption and noise

specific space consumption is high – needed new broad corridors are problematic to be realised.

An alternative transportation concept is useful only if it is clearly superior at least in these two aspects and feasible only if its financial concept is acceptable.

Before we published Autoshuttle, we made extensive research on energy consumption of different traffic modes as well as specific ratios of traffic capacity versus needed space. The results are:

Individually travelling cars have a high energy consumption, intolerably high at high speed, because of the high air resistance per car. An individual car on a pallet bears an even higher air resistance.

Formation of convoys by uncovered cars results in a small reduction of air resistance per car and thus energy consumption only. The air turbulences are still prominent. This was the result of the Prometheus-convoy-concept of Volkswagen in the 1980’s (E. Fiala, ATZ 90 (1988), 429; W. Dreyer et. al., VDI Berichte 699, 311 (1988)). Convoys of cars on pallets bear an even higher air resistance.

Formation of convoys by cars being transported in streamlined cabins having congruent front and rear parts yields much lower air resistance per cabin and thus energy consumption. This holds for convoys of five cars length on. The large cross-section of such cabins makes shorter convoys or single cabins ineffective.

Fast convoys travelling at constant speed yield the highest traffic capacity.

For example, Autoshuttle-convoys have an average fuel consumption equivalent of 102 mpg per transported car including all additions like empty runs, on-board consumption etc. (Annex A4). If Autoshuttle was designed not with cabins but open pallets, consumption would increase to approximately 30 mpg. If Autoshuttle operated with open pallets without formation of convoys, approximately 10 mpg would result.

If speed was reduced in favour of energy consumption, attractivity and traffic capacity would be lowered. Thus, fast cabin-convoys combined with rendezvous-manoeuvre and non-moving points in order to pass non-wanted intermediate stations at speed are the only choice combining a solution to both above-mentioned problems.

Additionally, we found that Maglev is perfectly suited for a track-guided system with many cabins. It has much lower energy consumption, lower initial costs, wear and tear than any wheel-based or air-cushion system. Noise is negligible at the Autoshuttle cruising speed of 112 mph.

The last paragraphs show that it is not worth installing an alternative transportation concept with individually moving cars or convoys formed from uncovered cars. Improvements upon conventional road traffic are too low.

However, cabin concepts must cope with storage for empty cabins and empty runs in order to compensate for unequal traffic flows. Both concepts are considered in The extremely low energy consumption respects empty runs for strongly unequal traffic flows during rush hours (see Annex 4). The extremely low space consumption respects extensive stations and storage areas (see Annex 7). The extremely high traffic capacity (see Annex 6) is possible with fast moving dense convoys only.

An alternative transportation concept must be feasible financially as well. Annex 10 shows that if at least 28% of the users of a parallel motorway in Germany change to Autoshuttle, the system becomes profitable. Bearing in mind the result of our preliminary survey yielding 96% acceptance of Autoshuttle (Annex 9), the needed changeover-figure of 28% appears achievable. This financial study respects all capital and operational cost, so of course including the cost of buying enough cabins for the highest demands and including the cost of a suitable dispatching system and empty cabin runs. Autoshuttle’s fares are 15% lower than the operational cost of driving on the conventional motorway (Annex 10). The user does not have to buy a special car or some special equipment for his car but saves 15% of the conventional travel cost instead.

So far, we have never read a reliable financial study on concepts based on special dualmode road vehicles. Our preliminary studies show that the public is reluctant to buy such special cars. These concepts would fail due to low acceptance. The infrastructure costs are high but revenues keep low. Autoshuttle is based on the use of conventional road vehicles – the basic feature needed for commercial success.

We do foresee Autoshuttle for high-traffic corridors. We do not see sense in providing a track-guided system for the distribution of traffic to each individual destination. Here the road is the better solution, maybe assisted by navigational systems, distance control devices etc.. Autoshuttle concentrates on an optimised loading and unloading process, so that the central part of a typical journey, i. e. along a high-traffic corridor, can be improved. Because of this, Autoshuttle can begin in a small scale, e. g. 15 miles long at an extremely congested corridor. Systems which need special equipment for the user can’t be started profitable in a small scale. People wouldn’t buy a special car, if for the next years it was useful only on short stretches of track. Even in industrialised countries, most of a car’s mileage is done on low to medium trafficked roads (e. g. in Germany only about 15% of the traffic volume is of the type "high-capacity corridor" (source: 1998-99 vehicle counting results of the German Ministry of Transportation), where a track-guided system is useful. Therefore, it is better to have no appliances for the guided mode on the road vehicles. These appliances would travel around in vain during 85% of the mileage of a car. Instead it is better to provide independent and optimised cabins for the critical 15% of the mileage.

Annex 12 shows the superior availability of Autoshuttle. The superior safety of the rail-embracing MAGLEV-system with continuous speed control of the cabins is evident.

In conclusion, we state that dualmode cars do not achieve their objective in that the interesting features of environmental friendliness and specific space consumption are improved only marginally when these cars travel on a track instead of a road. Travelling on a road, which will remain the major part of the car’s mileage, disadvantages have to be accepted due to the extra appliances. Transporting conventional cars on open pallets is not advantageous either.

Autoshuttle shows prominent improvements in environmental friendliness and specific space consumption. The conceptual disadvantages of the cabins like empty runs, investment costs and storage area are respected in the detailed calculations at the Autoshuttle website. Despite this and due to the conceptual advantages of cabins, Autoshuttle bears clearly superior financial aspects for user and operator, environmental friendliness, traffic capacity, use of space, safety, individuality, reliability and door-to-door average speed.

Our technical and financial studies show exact calculations, which have been confirmed to be realistic by many technical experts and a high-tech financial advisory company. Francis Reynold’s general remarks on assumed principal disadvantages of pallet systems lack this accuracy. Instead, we would be interested in direct comments on our detailed calculations.


Last modified: June 26, 2000