> For the complete documentation index, see [llms.txt](https://docs.rekor.ai/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.rekor.ai/rekor-command-r/time-explorer/work-zone-impact-calculations.md).

# Work Zone Impact Calculations

Time Explorer surfaces a set of metrics that describe how much a work zone is affecting traffic, and how that impact is trending over time. Here’s what each one means and how it’s derived. 

**Speed & Flow** 

| **Metric**             | **What It Shows**                                                                          | **How It’s Calculated**                                                   |
| ---------------------- | ------------------------------------------------------------------------------------------ | ------------------------------------------------------------------------- |
| Current Speed          | The live, real-time speed on the road segment                                              | Real-time probe/GPS speed data for the segment                            |
| Expected Speed         | What’s normal for this segment at this specific time and day, independent of the work zone | Historical average speed for that hour of day and day of week             |
| % Below Expected Speed | How much slower traffic is moving than what’s typical for this time and place              | (Expected Speed − Current Speed) ÷ Expected Speed × 100                   |
| Free Flow Speed        | The speed vehicles could travel with zero congestion                                       | Historical speed observed during uncongested conditions (e.g., overnight) |

**Time Impact** 

| **Metric**              | **What It Shows**                                                     | **How It’s Calculated**                    |
| ----------------------- | --------------------------------------------------------------------- | ------------------------------------------ |
| Travel Time Index (TTI) | How much longer the trip takes versus ideal conditions                | Free Flow Speed ÷ Current Speed            |
| Time Delay              | The actual added time caused by the work zone, in minutes and seconds | Actual travel time − free-flow travel time |

 

**Overlap Detection** 

| **Metric**                | **What It Shows**                                                                                   | **How It’s Calculated**                                                                            |
| ------------------------- | --------------------------------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------- |
| Overlapping Road Segments | Whether this work zone shares road segments with other active work zones, which can compound impact | Geographic comparison of work zone polygons against the road network, summarized in plain language |

**Trends & Comparisons** 

| **Metric**                           | **What It Shows**                                                    | **How It’s Calculated**                                                                   |
| ------------------------------------ | -------------------------------------------------------------------- | ----------------------------------------------------------------------------------------- |
| Daily Trend – Current Speed          | The typical hour-by-hour speed pattern for this segment              | Current speed values aggregated by hour of day                                            |
| Daily Trend – TTI                    | The typical hour-by-hour TTI pattern for this segment                | TTI values aggregated by hour of day                                                      |
| Live Speed vs. Creation Day Baseline | How today’s speed compares to the day the work zone was first opened | Today’s average live speed vs. the average speed recorded on the work zone’s creation day |
| Live TTI vs. Creation Day Baseline   | How today’s TTI compares to the day the work zone was first opened   | Today’s average live TTI vs. the average TTI recorded on the work zone’s creation day     |


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