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Traffic data collection provides the foundation for transportation planning and policy
4 Min Read
At all levels of government, decisions regarding wear and tear on highways and bridges, congestion and safety networks, and peak period traffic flows depend on accurate data collection. Data also helps states secure much-needed federal funding for their roadway networks.
Unfortunately, these same state and local governments often face limited budgets and dwindling staff. This can make it difficult for agencies to find the time and resources to evaluate available data collection technologies or thoroughly check on the data work being done by vendors. Compounding this issue is the fact that many programs are based on low-bid contracts, prompting vendors to limit their data equipment standards and testing to provide a lower fee.
All this, of course, can result in poor data collection. And poor data collected today can negatively impact development and expansion decisions, as well as maintenance needs and improvements, for the foreseeable future.
Road tubes provide an accurate and affordable means to collect axle-based traffic data. The catch, however, is that they must be installed correctly, which can be tricky.
First and most importantly, all equipment used in conjunction with road tubes must be tested and checked to assure that it is working properly. This means the air switches within the road counters must be working at similar sensitivities. The counters, in turn, must be free from debris or corrosion.
Only new or slightly worn road tubes should be used. Tubes should be knotted, and pressure tested to ensure they do not leak air. This will guarantee a good pulse in the road tube which will be accurately received by the counter. Road tubes that leak or fail to provide equal air pulse will inevitably produce errors in axle data collection.
Location is essential for improving the performance of the counter and assuring data accuracy. Road tubes should be perpendicular to the road edge and struck straight-on by passing traffic. Ideally, traffic should be free flowing, with minimal congestion or backing. Congestion or stop-and-go traffic will result in the appearance of low volumes. Areas where the roadway curves or congestion regularly occurs will generate errors in the data collected.
The counter itself must be able to decipher the pulses it receives correctly. This can be complicated because the counter has to decipher numerous issues which can impact the data collected. Tailgating, for example, may be misinterpreted as a truck or longer single vehicle, such as a limousine. Phantom pulses, which occur when air traveling down the road tube hits the far end of the tube and echoes back toward the counter, can confuse the counter into thinking it is seeing traffic where there is none.
There are, of course, alternate technologies that can be employed for data collection, but each comes at a price. The piezo method, for example, is the technology that most closely resembles the road tube method. Like the road tube, the piezo is embedded in the roadway perpendicular to traffic and registers the axles of vehicles as they cross. Far more accurate and much more sensitive than the road tube, the piezo will also last much longer in the roadway. Imbedding the sensors in the roadway, however, is costly, time-consuming and labor intensive. As a result, use of the piezo method tends to be reserved for long-term or permanent data collection programs.
Two other technologies—radar and video—are also used to collect traffic data. Because radar and video are non-intrusive, they are often preferred to road tubes on larger roadways and interstate-level routes where high speed and traffic volume significantly increases the risk to operator safety. Using non-intrusive data collection methods still provides insight into how the roadway is performing and traffic type.
The costs and risks to safety cited above necessitate the need for traffic engineers to have multiple solutions in their toolbox to complete the most accurate and safe data collection program possible. With the rapid advance of AI solutions, the hope is that new, AI-enhanced video and radar technologies will soon be available on the market to help alleviate the gaps that currently exist in non-intrusive data collection efforts. This will enable state and local governments to accurately—and safely—collect the traffic data needed to inform transportation planning and policy decisions in the future.
