Show U. U S. S Disguises Testing Device To Spy on Automobile Drivers a w of A black rubber tube laid across the highway and connected at either end with a simple Instrument staked at the side of ot the road forms the basis for analysis of how the motor public behaves in its use of ot the high ways This special study Is being made by the federal bureau of public pub pub- lic Uc roads The tube is inconspicuous and looks much like an expansion Joint one one ne of its good features Most motorists will wiil not see the tube ane and will not be aware of making makin a rec rec- ord Other devices such as 81 checking check ing b by observers or by motion motion- picture records are less useful because because be be- cause the they are likely to make drivers era ers self conscious and cause them to slow Ilow down for fear of a speed peed trap A. A record of natural driving on a representative stretch of road Is what is wanted The tubes are placed rt et foot 50 Intervals intervals In in- on the stretch of road under understudy study study study-a a half halt mile perhaps When an automobile crosses a tube a wave or puff of air is I. forced into the roadside instrument and moves move a diaphragm which causes an electrical elec dec contact The tubes are disconnected dis connected at the middle of the road so that a vehicle passing on one side of the road does not register on the instrument on the other side Wires run to a recording in which a strip of paper unrolls under a set et of ot pens Each passing car leaves a pair of pen strokes- strokes for tor front and rear wheels wheel Knowing the spacing of ot the tubes and the speed of the moving paper it is easy to calculate the speed peed of any car The device is particularly useful in studying the passing of slow ve ye- hides by faster futer ones On a two- two lane highway the marked n-marked II strip reveals the faster car overtaking the slower then swinging across the center and registering on both lanes then running in the left lane and finally swinging back to the right Distances and speeds can be calculated exactly and b by ing tag many it is possible to compute for example how long a straightaway stretch should be to tomake tomake make passing safe and easy A single Ingle tube with the roadside instruments connected to an elec ii-ic ii counter makes a convenient and inexpensive device for registering the number of vehicles using 4 road |