Resets - Roughness

Overview

This page outlines the Resets applied to Rougnness (Naasra counts) by different treatments. It is important to note that what is described below is only the pattern assumed for roughness reset. The Default Road Network model allows you to modify the key values related to roughness reset using the Lookup values. This means you can control the relative reset applied by different treatments without having to modify the underlying C# model.

Note

The road default model is currently used mainly in New Zealand, where for historic reasons Roughness is expressed using Naasra counts instead of the more international International Roughness Index (IRI).

If you are outside of New Zealand and want to convert your model to one using IRI, you can do so by simply exchanging default values that currently pertain to Naasra to values that relate to IRI. A more robust and longer term solution, however, would be to modify the default model in Visual Studio and then recompile the model .DLL for your own use. If you are interested in this approach, please contact Lonrix.

Preservation and Holding Treatments

It is well-established that light Preservation treatments such as Chipseals and Thin Asphalt surfacings do not reset roughness completely. In most cases, light preservation treatments only effect a slight improvement in roughness, and the roughness after treatment is typically well-correlated with the roughness before treatment.

The model assumed for roughness reset under Preservation treatments is dependent on two factors:

  • Exceedance Factor - factor below which the roughness before and after treatment is assumed to remain the same

  • Improvement Factor - factor by which the roughness portion above the exceedance threshold is reduced by the treatment

The concept is illustrated by the figure below:

Figure 1: Roughness Reset Concept

An example calculation for two different improvement factors is shown below:

Figure 2: Roughness Reset Example

The model allows you to set the Exceedance Factor and Improvement Factor individually for Chipseal-or-Asphalt-Surfaced roads. Different factors can also be specified depending whether the road is in an Urban or Rural setting, and on the traffic class in the lookup sets ‘reset_exceed_thresh_naasra’ and ‘reset_perc_improv_facts_naasra’. See this link for details on these lookup factors.

Rehabilitation

For Rehabilitations, a fixed reset value for roughness is assigned depending on the surface type and road category (traffic intensity). See this link for details on these lookup factors.