Show U. U S. S Disguises Testing Device o c To rI Spy on Automobile Drivers i I A black rubber tube lube laid across the highway and connected nt at either cither I end with n a simple instrument staked slaked nt at the th side of the road forms torms the basis for analysis of how lieu the motor public behaves In III Its use of the high ways was This special study stud Is being made by b the Uhe federal fed rill bureau of pub public lic lie roads The tube Is inconspicuous and looks much like an expansion joint one one of its good features Must Most motorists will not see sec the Ule tube and will not be aware of making a II rec ord Other devices such ns as check check- checking checkIng checking ing by b observers or by motion notion picture records are less useful be be- because because cause CHuse they are likely to make drivers ers self-conscious self and cause calise them to slow down for fear of a speed trap A record of natural driving dri on a n representative stretch of road is what Is wanted The tubes are arc placed ft rt foot 50 in intervals intervals on the stretch of road rOld under understudy study study study-a o half mile perhaps When an automobile crosses u a tube n a wave or pun puff of all air is forced hito tile the roadside instrument and moves a diaphragm which causes an on elec elec- electrical electrical contact The tubes lubes are arc dis disconnected disconnected connected at the middle of the road so that n a vehicle passing on one side of ot the road does docs not register on the till Instrument on the other side Wires run to n a recording apparatus in which n a strip of paper unrolls under n set of pens Each passing car cur leaves a pair of pen strokes strokes- for fur front and rear wheels Knowing ln the spacing of the tubes and the speed of the moving mavins paper per It is easy to calculate the speed sp ed of any car i The device is particularly useful in iu studying the passing of slow ve ve- vehicles e hicks by faster ones On a n two two- lane 1 highway the 1 ii marked n-marked strip I reveals the Ule faster car clr overtaking the slower then swinging across neross the center und and registering on both lanes then running in lI the Uie left Idt lime lane and finally swinging back to the right Distances and speeds can be calculated exactly exact and by b tabulating tabulating ing many man It is possible to compute for or example how hw long lone n a st stretch should U bo to tomake tomake make male passing safe and easy A single tube with the Ule roadside instruments connected connect d to an nn elec clec electric counter makes n a convenient nt and inexpensive e device for foi fo registering the number of vehicles using a II road |