Show Highway Traffic Trade Is i Counted Exactly bythe by bythe byI I the Robot Watchman I Provides Basis for Cor All Safety Regulations ington A roadways roadway's Washes Washington A i I traffic pattern which varies I with the day of the week the hour of the day and the day dayi i of the month is the dictator of all safety and traffic regu- regu 1 I lation lotion policies as well as the selector of all new highway undertakings I Robot infra infra red light beam watchmen are one of the new I mechanisms by which highway engineers engineers en i now keep a hour 24 watch I on roads where changes are needed red Infrared beams directed across the highway onto photoelectric cells cell now keep watch and are able to count as high as vehicles an hour Operation of the device costs a year compared with I for a continuous manual counter check I The photoelectric photo counter is seldom seldom sel dom noticed by even the most observing observing ob serving motorists It consists of ot two short posts with cross arms one on either side of ot the road The post supporting the light source is equipped with two ordinary automobile automobile auto auto- automobile mobile headlight bulbs whose light is rendered invisible by filters This eliminates any confusion which might result in night traffic Parallel Parallel Paral Paral- lel leI beams projected across the road and nd spaced 30 inches apart provide provide pro pro- provide vide a current path to the photo tubes on the opposite post Count Is II Almost Perfect Whenever the two light beams are Intercepted simultaneously the interruption in is recorded by the counting count count- ing mechanism in the receiving box At the end of each hour the printing panting apparatus stamps the day of the week the time and the cumulative traffic total It If the current should fall fail the time of the failure is recorded recorded recorded re re- re- re corded as well as the number of ot vehicles counted up to the break break- down Errors in h the count never exceed 5 S per cent of ot actual traffic volumes and are usually held to with within 1 or 2 per cent of ot accuracy There are however s several veral unavoidable sources of error such as when two cars passing the counter in opposite opposite site directions Intercept the light beams at the same time Only one vehicle is then recorded Phantom trucks have been found which pass by the electric eyes without being seen This mystery mystery mystery mys mys- tery was solved when it was observed ob served that the ghost trucks were painted either white or aluminum with the result that at certain hours during spring or fall faU days sufficient cleat clent light was reflected a 8 receiving unit which faced north so that the light ordinarily furnished by the light source was wa replaced Most of the freak errors encountered cancel out and the automatic recorders can be relied upon with witha a minimum of attention to provide accurate hour 24 information |