In this last of three posts we will look once again at a study entitled, “Mitigating Work Zone Safety and Mobility Challenges Through ITS” (Report # FHWA-HOP-14-007). The authors spend some time in the section on off-the-shelf systems discussing system specifications. “Experiences from the two system deployments indicated a need to provide enough detail in the specifications to allow vendors to bid competitively, but not so much that it excludes many of the vendors from participating. The key is in understanding what features, data, functions, etc. are essential to meeting the system objectives.”
A more prescriptive specification will hold up better over time. So specify outputs, not technologies. You don’t want to have to change your specification as technology evolves. And you also don’t want to miss out on improvements as they become available. So, whenever possible, a more prescriptive approach is best.
Conversely, some detail is still important. For most systems you should specify the quantity of devices. This, more than anything else, does provide an apples-to-apples comparison. In the case of sensors, consider your needs first. If traffic flow is what matters most, allow any type of sensor so long as it sends the data in real time. But if volumes or lane-by-lane counts are important, say so and allow the vendors to find the best method of providing that.
The goal of any specification should also be something requiring as little input from the project designers as possible. Engineers can’t be experts on everything. Experience has shown a reluctance on their part to include work zone ITS when they are required to decide on the quantity and type of devices. They design roads, not ITS systems.
In a post dated February 18, 2014 we discussed the Texas approach to this problem. Separate specifications for large and small queue warning systems that designers can plug into any project. This approach has since been adopted by several states including Indiana, Illinois, and Oregon. The same thing could be done for any off-the-shelf system.
Custom systems should always go through a systems engineering approach. A detailed needs assessment and identification of devices and methods to meet those needs are the only way to succeed consistently. But agencies will be more willing to do that work once they have had success with these off-the-shelf systems. They will learn more about the different devices in those systems that they can then apply to more complicated deployments.