It was just a few short years ago that we were all wishing for more and better data. We still are in the work zone world, but the systems operations world is suddenly inundated with data. Cell phone data, loops and radar sensors, toll tag readers and BlueTooth readers are now sending traffic information to your local traffic management center faster than it can be absorbed.
So we in the work zone world find ourselves in a tough position. We are offering data to these same traffic management centers that they neither want nor understand. They aren’t making use of the data they have now so they can’t justify the effort to acquire more of it. And because they are systems operations folks they don’t yet understand the need for spot speed detection on a road where they already are getting cell phone probe data.
This is a battle we are all going to fight soon, if you aren’t already, so let’s review the differences. Systems operations needs to know how traffic is moving by route or through the region. Work zones are more focused, looking only at traffic movement over the affected route in or near the work zone. Operations goal is to identify problems, report them to the public and thereby divert traffic onto the unaffected routes. Work zone practitioners do the same thing, but they are more concerned about correcting the problem, whether it’s just a crash within the work area or a slow down caused by the work zone design. In short, systems operations is a “big picture, 30,000 foot” look at a region. Work zones must be much more detailed or granular. They want to know where the problem begins so they can more easily identify the cause and correct it. This is not to say that operations is not also concerned with incident response. They are, of course. But work zones are the #1 cause of non-recurring congestion. They warrant more attention for this reason alone.
The FHWA agrees. The Federal Work Zone Safety & Mobility Rule says we must collect data on our work zones and use that to monitor and improve their performance. That data shall include speeds or volumes through the work zone and at key locations within the work zone including the advance warning area, the taper and the work area itself. The question then becomes, “How do we collect this data in the most efficient and cost-effective manner?”
Probe data is less expensive. And it is already being collected. If an agency is paying for the service, they already know how traffic is moving over that route. However, they won’t learn about problems as quickly because probe data is reported over road segments. Highway road segments can be as little as a mile long, but more often are much longer, especially in rural areas. So it can take several minutes before they see the average speeds drop over an 8 mile long road segment.
They also won’t know where the problem within that segment is located. So any effort to correct it will necessarily take longer. Longer response means the delay will become worse leading to more secondary crashes and greater driver frustration.
This is even more important if you are using the system for more than data collection. If it is also being used for something like a queue warning or a dynamic merge application, you must have immediate notifications and those are not available from probe data.
Portable speed sensors have another important advantage. They are portable. They can be moved as the construction work moves to gather data at critical locations. So, although the lane closure has moved, you will still know how traffic is moving at the new taper or lane shift.
Yes, these systems cost money. And resources are limited. But recent studies show benefit / cost ratios as high as 7 to 1, even 10 to 1 in some cases, so it is truly a good use of taxpayer dollars. And as we have discussed, no other technology gets us the detail we need to make our work zones as safe and efficient as they can be.