Highways and Highway Transportation

by George R. Chatburn

The Association urges abolishment of the red for automobile tail lights and the substitution of yellow (white). There are other reasons why this should be done; one of them, a white light will illuminate the number tag much better than a red light. In fact Ohio requires a red light shining out behind and a white light to illuminate the tag. On the other hand by the different colored lights one can distinguish whether one is going toward the front or back of an automobile, a thing of importance, sometimes.

This may be far enough to go at the present time, but later the standardization of other signal and guide lights would be well. The red light on street obstructions should be abolished. Better a bright white light for with good illumination the danger will often disappear.

Road and Street Lighting.

—While road and street lighting are primarily for the purpose of promoting safety, they, as signs and guides, are here treated under the heading of comfort and convenience to the user.

Like other things pertaining to roads, lighting has during the past few years seen wonderful development. Open-arc lights have all but passed out of use. Even in the field of incandescent lighting many improvements have and are still being made. Efforts have been made to cater to the esthetic sense and create beauty by artistic shapes and sizes of lamps and by harmonious groupings. Safety, comfort, and esthetic design cannot always be combined, then one or the other must give way.

Silhouette vision, that is, where the object appears dark against a lighter background, requires a much less illumination intensity than direct or detail vision. In the first case the object is between the observer and the light while in the second case the light is reflected from the object to the observer. Then there are spot lights and flood lights where the light is thrown directly upon the object and as little as possible allowed to disperse into surrounding space. Dean Ferguson[234] has pointed out that safety lighting is secured by any illumination that will reveal clearly the presence and nature of a danger, and also that low illumination intensities used in silhouette effect may serve for safety at a greatly reduced expense. Much of street lighting is of the silhouette type, depending on the relative positions of the observer, the illuminant, and the object to be seen. As we approach a post or sand pile on the street it appears first as a black object in silhouette, as we come nearer the reflected light becomes more intense and the object is seen in detail. There seems to be a sort of twilight zone between these two conditions where the visibility is least. The silhouette vision appears to be best when the intensity of the reflected light is least, and vice versa for the detail or direct vision. The indeterminate place between the two where visibility is least is, of course, where the light behind is equal in intensity to the reflected light in front. One object of the illuminating engineer is so to arrange the lights as to avoid as far as possible points of low visibility. This he does by the size and spacing of the light units, their height of suspension and the shape and setting of the reflectors. These same elements enter into the avoidance of glare.

In city and street lighting it is nearly always desirable to illuminate the buildings as well as the road surface, so that the type of lamp used is entirely different from that desirable on country roads where only the surface of the roadway needs to be lighted. Ornamental lights of the luminous arc and the incandescent types are used. The former where a large amount of intense light is wanted, and the latter where smaller units will answer the purpose.

The latest road lighting is, perhaps, that developed for the “Ideal Section” mentioned heretofore.[235] Here it was important to concentrate the light on the roadway instead of diffusing it upward and over the adjoining fields, to have a flexibility of arrangement that would keep the light in line with the surface of the roadway, and that the cost should be reasonable. The scheme developed contemplates placing the lighting units on adjustable brackets 35 feet above the surface of the road, spaced 250 feet, staggered. They can be set for varying grades, for curves, or for the lighting of a portion of the roadside if thought necessary. The unit consists of a nest of three reflectors, one within another, and with an opening in each one side of the lamp. These collect and reflect the light to the surface as shown in the figure. The detailed article should be consulted by those who are further interested.

City Traffic.

—Projectors suspended above a traffic officer illuminates him and his semaphore much as spot lights are used in theaters and flood lights to illuminate statuary and buildings. Many of the busy cities are installing color lenses in the towers (crow’s-nests) to regulate the traffic. The colors which are used both day and night are standardized as follows: Red, to indicate “Stop”; amber, to indicate “Change of traffic”; and green, to indicate “Go.”