🧮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