As movement across country entails traversing rough ground, the tracks of a roadless vehicle must permit of the absorption of obstacles. This absorption is attained by springing the tracks. In an unsprung machine, obstacles are either crushed into the ground or the vehicle has to lift itself over them. In both cases the result is injury to the machine, and loss of power and discomfort.
It stands to reason that the vehicle must be durable, simple and easy to maintain; also that the ton-mile cost must be low. As regards this latter requirement, experimental machines have so far proved that this is a possibility. A one-ton roadless Guy Lorry recently travelled from London to Aldershot, and its ton mileage was fifty-two to the gallon. It has also been worked out that the cost per ton-mile of the Sentinel tractor, “including overhead charges, depreciation, interest on capital and all running charges, and allowing for a 20-tons net load for a reasonable number of working days in the year,” will be slightly under twopence per ton-mile.
SENTINEL TRACTOR
[Face p. [80]
In the future, the types of roadless vehicles are likely to be great as the surface of the ground differs in various countries; also fuels of all kinds are likely to be burnt, such as petrol, oil and coal, and in tropical countries, where these fuels are scarce or expensive, producer gas is almost certain to become the main motive power.
The most remarkable achievement as yet carried out by roadless vehicles is undoubtedly the crossing of the Sahara from Touggourt to Timbuctoo, during the winter of 1922–1923, by Citroën motorcars fitted with half tracks invented by Monsieur Kegresse. The distance travelled was three thousand six hundred kilometres, and the time taken was twenty days, that is on an average one hundred and twelve miles a day. All machines returned safely, and the total journey there and back was over seven thousand kilometres.
The nature of the country crossed was by no means uniform, for it was sandy, rocky, mountainous and, in the neighbourhood of the river Niger, covered with tropical vegetation. To build a railway from Touggourt to Timbuctoo would cost, at the lowest reckoning, a thousand millions of francs—possibly much more; this alone accentuates the importance of the achievement and its interest to us, for the Empire contains thousands of square miles of roadless country.
I fully realize that, though the roadless vehicle can replace the motor-car, it cannot replace the railway, if the railway is an efficient one. This is, however, not the problem. The problem is, first to bridge the gap between the producer and the railway, and secondly to create in undeveloped countries sufficient wealth to enable more railways to be built. Co-operation with existing railways, this is what must be aimed at.
CROSSLEY-KEGRESSE CAR
[Face p. [82]