Before the appearance of the bicycle and the car, vehicle speeds seldom exceeded 15 km/h. Thus the horizontal curvature of the road was only important in so far as it was necessary to enable long animal-teams hauling carts to negotiate tight bends. On minor roads a 15 m radius was adequate and 25 m was ample for major highways. However, by the turn of the century the self-powered vehicles had raised that minimum to 50 m. This
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led to road curves being frequently no more than kinks between pieces of straight alignment. Sight distance was an irrelevancy at the low operating speeds and, with the coming of the bicycle, was solved more by bell-ringing than by realignment.
Section 3.3.4 described how the older roads had often employed continuous and steep cross-slopes on both straight and curved sections in an often futile attempt to drain water from the road surface. However, banking (i.e. superelevation, Section 19.2.2) on curves was uncalled for at 15 km/h. The car soon changed the situation. Steep cross- slopes had to be removed from the straight lengths of road and superelevation provided at curves to encourage drivers to stay on the correct side of the road as they cornered. The provision of superelevation began in 1908 and met stiff opposition from the owners of horse-drawn vehicles whose lack of centrifugal force when cornering led to them slewing down the banking.
With all vehicles travelling at relatively low speeds and possessing short stopping distances, priority was usually by might rather than by decree. The few measures that were introduced, like the U.K. Red Flag Act discussed in Section 3.5.2, were largely aimed at preventing a few being a nuisance to many. The car changed all this and brought some new traffic disadvantages as well. Consequently, the practice of traffic engineering was born.
Traffic signals were introduced at a pedestrian crossing in London in 1868 and modern-style traffic signals in Cleveland, Ohio in 1914. The first roundabout was built in 1903 in France. Detroit claimed the title ‘Motor City’ in 1909 as the heartland of U.S. motor-vehicle manufacture. It obviously saw this as carrying traffic safety obligations as well and formed a Traffic Division of 13 policemen in that same year to control traffic via hand signals. In 1911 the surrounding Wayne County introduced centreline marking, initially on narrow bridges, and the city introduced pedestrian crossings. In 1915 the Traffic Division produced the first stop sign and in 1918 the first three-colour traffic light.
Route marking began with a 1704 Maryland law requiring trees beside a route to be marked with an elaborate system of notches, letters and/or colours. One South Maryland road has retained its name as ‘Three Notch Road’. More conventional numbering began in Wisconsin in 1918 but major routes were more commonly distinguished by coded bands of colour painted on roadside poles and trees.
One measure of some historical significance concerns driving on one side of the road or the other. During most of transport history such a requirement was irrelevant. Few roads could take wheeled vehicles and those that could were rarely wide enough for two vehicles to pass with ease. One vehicle, under the right-and-might rule, would pull aside for the other. Some Roman bridges did permit two-way traffic, with each bridge having its own priority arrangements. Of course, vehicle speeds on such bridges were so low that drivers did not require any advance knowledge of right of way.
The need for a clear rule grew as wheeled vehicles became more common in the 17th century. On vehicles with a seated driver and one line of horses, the use of the right hand for the reins and the whip led to the driver favouring the right and therefore passing to the left so that he could judge the passing manoeuvre. This was very much the case with the smaller English vehicles. However, with more than one line of horses the driver tended to the left so that his right hand could manage the full set of reins. Giving good centreline sight to the driver then favoured driving on the right. Such larger vehicles were more common in continental Europe. Similarly, those in charge of a string of pack-horses would hold the lead horse by the right hand and thus found right-hand passing easier.
Where firearms were needed, the right to left direction of the barrel across the body also favoured moving to the right. A major impetus for right-hand driving in the U.S.
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came from the design of the Conestoga wagon, made famous as the ‘Prairie schooner’ that led to the winning of the West. The wagon was operated by the driver walking or riding a ‘lazy board’ alongside the vehicle and using his right hand to manage the horses and operate the brake lever. Thus passing required moving to the right to give the driver forward vision.
The first national decree was introduced in Saxony in 1736, requiring travellers to keep to the right when crossing a new bridge over the Elbe, whereas English legislation in 1756 required traffic on London Bridge to keep to the left. The rule became widespread in Britain after an Act of 1835. Right-side driving was encouraged by turnpike regulation in Pennsylvania in 1792, with the first general laws occurring in New York in 1804 and in Canada in 1812. Left-hand driving persisted in the U.S. on the National Pike (Section 3.4.3) until the 1850s.
3.6 SURFACES