What You Need To Know About Routable Road Networks

Maintaining detailed, accurate routable networks in your computer-aided dispatch (CAD) system has the potential to save precious seconds in response times, discover insights, and allows for increased efficiencies in emergency response. While not a requirement for Next Generation 9-1-1, these data layers have the potential to provide meaningful impact by increasing public safety for jurisdictions across the nation.  

What are routable road networks?

A routable road network is a detailed road network data layer designed for use in computer aided dispatch (CAD) systems to provide routing recommendations to first responders. These layers differ from next generation 9-1-1 (NG9-1-1) road centerlines as they may incorporate additional details necessary for routing. Routable road networks should represent any possible route a response vehicle could take to access an incident faster including through parking lots, alleyways and private roads as well as avoiding road closures and one-way streets.

Typical road centerline (RCL) layers do not include the level of detail required for efficient emergency response routing. Factors like directionality, impedance, unnamed or missing segments and topology have a significant impact on routing quality, and when unmaintained can lead to inefficiencies in response.

To develop a usable routable road network, your jurisdiction should consider the following factors:

• CAD System: The specifications of your network will rely on the type of CAD system your jurisdiction is using. Before developing a routable road network, work with your CAD vendor to understand the requirements of your routing engine and tailor your GIS to those requirements.
• Impedance or Friction: Impedance identifies factors that slow the flow of traffic like roundabouts, lane mergers or speed limits. Speed limits can be maintained as a field in the RCL layer or as a separate table depending on your CAD system.
• Nodes: Nodes identify intersections and connecting roads in your data and contain information on important details related to traffic flow and friction to drivers.
• Spatial Representation: This data should represent any possible route an emergency vehicle could take, including parking lots and private roads. To ensure accurate routing, mark turn restrictions segment-by-segment and elevations of overpasses and underpasses.

Real-world examples of routing oddities

Could your routable road networks use a facelift? Check out these before-and-after’s for some inspiration.

Can you spot the difference? Here’s a clue: Ensure that all of your roads are pointing in the right direction.

In this transformation, we can see that the original road centerline is running through the center divide of a roundabout. To ensure appropriate routing, our team added geometry to represent every direction of the road.

In this example, we can see that the original data showed only centerlines for each road. The DATAMARK team remediated this data to reflect the direction of each lane to ensure appropriate routing.

When maintained appropriately, 9-1-1 routable road networks provide first responders with information necessary to locate incidents faster and with greater efficiency. Accurate routable networks incorporate key details related to impedance, nodes and spatial representation to steer responders in the right direction. To learn more about routable networks and the related services DATAMARK offers, visit our services page or check out our webinar on the subject.