The Traffic Corner: Testing Traffic Counters
Counter Tester
When I was an intern, I was put in charge of inspecting and measuring quantities on several street lighting projects. I measured about four miles of installed cable. The contractor questioned my quantity—saying it was low—and said I was shorting him. I met him early the next day, expecting a long day of spot checking. The first thing I did was lay out my 25-foot tape measure and check to make sure my measuring wheel was accurate. I asked him to do the same. His wheel said the 25-foot tape measure was 28 feet long. We did the math and his quantities were off by the 28/25 ratio. Case closed in about half an hour.
Spring is here (we hope), and it is a good time to make sure your field equipment is in working order. Are you sure the traffic data you have been collecting is accurate? We test all our counters every three months with a Jamar traffic counter tester in addition to visually verifying our counts every time we set up in the field. The traffic counter tester blows a prescribed number of air pulses so we can test the accuracy of our air switches (volumes as well as speed and classification data). We also do a manual test on our Jamar manual count boards—punching in a prescribed number on each button. It seems logical to me that you need some way to ensure your counters are working properly.
One of our public sector clients has 20 tube counters of its own. This winter the agency had us go through our test regimen on their counters. Seven of their 20 counters had at least one bad air switch. Staff had enough time to send in their counters for repair and still get them back to start collecting data this spring.
I am guessing there is an intern somewhere who used traffic counters last year but didn’t think to question the accuracy of the equipment. Let’s make testing a habit so we all collect accurate data. LTAP
(Mike Spack, P.E., is the president of Spack Consulting. Before starting his firm, Spack worked for the City of Maple Grove as traffic engineer. He is a regular contributor to the newsletter, writing brief articles on traffic engineering topics.)