Introduction to our Calibration Feature
For many transportation projects, one of the first questions asked is: “How many trips happen on a particular roadway or corridor?” Traffic counts are often available for large road segments, but they are not available for all of the roadways that transportation professionals want to analyze. We launched our Calibration Feature to help our users estimate counts on all roads with StreetLight InSight.
The Calibration Feature utilizes additional data and analytics to scale StreetLight Index values to estimated counts. There are two options:
- “Calibrate with my Zone Counts”: You can bring in additional data by either uploading AADT (or similar counts) for roads in or similar to your study area.
- “Calibrate with StreetLight AADT”: Leverage our 2017 AADT values as your calibration data set.
No matter which option you choose, the Calibration Feature is an easy way to convert StreetLight InSight Index values into the industry-standard unit--estimated counts.
Calibrating our Metrics with your own count data is a feature available to all subscription levels. Calibrating with our 2017 AADT data is available to those who have a Gold or Platinum subscription. The Calibration Feature can be used in the following Project Types: Zone Activity Analysis, O-D Analysis, O-D with Middle Filter, O-D to Preset Geography, and Segment Analysis.
Here are few important things to keep in mind when using the Calibration Feature:
- If you select all of 2017 for your Project’s Data Period, StreetLight InSight assumes that the calibration data represents all of 2017. If your calibration data is actually from 2015, you are making an implicit assumption that travel behavior in 2015 was the same as 2017 for these road segments.
- If you selected a data period of all 2017, but your calibration data was only from January 2017, you’ve made an implicit assumption that all of 2017 was the same as the month of January.
- Note that the StreetLight AADT is calculated for 2017. If you’re including data from other months or years in your Project, you’ll be making an implicit assumption that all of 2017 was the same as the data period you’ve selected.
Step 1: Zones and Zone Sets
To get estimated counts from a Project, start by creating a Calibration Zone Set. To do this, you can upload your own AADT, ADT, AWDT, or AAWDT information. If you have access to StreetLight’s 2017 AADT Metrics, then you can calibrate your project with those analytics. If you are calibrating a Zone Set with 2017 AADT, you can upload a Zone Set without adding calibration information to your Zone Set first. To learn more on how to create a Calibration Zone Set.
Note: It is perfectly fine to have a Zone Set where some Zones have calibration data and some don’t. It’s also fine to have anywhere from one Zone to a hundred Zones when using “Calibrate with my Zone Counts”. When using “Calibrate with StreetLight AADT,” we recommend using between seven and twenty zones for optimal results.
If you are calibrating with “My Zone Counts” you will create a Zone Set that contains your count data, learn more on creating Calibrated Zone Sets. The guide below is an overview of the information you will need to use the Calibration Feature with “My Zone Counts.” It uses an example from Montgomery County, MD.
Calibrating with My Zone Counts
Calibration Zones can be either polygons or lines, and they must always be Pass-through. When adding Calibration Data to your Zones you must include the following fields:
- Calibration Data: Choose whether your counts are AADT, ADT, AWDT, or AAWDT data.
- Calibration Value: Input your known counts.
- Personal Traffic Ratios, Commercial Medium Duty Traffic Ratios, and Commercial Heavy Duty Traffic Ratios: If you have information on the breakdown of traffic, you will input it here. If not, use our default settings.
Pro Tip: Your Calibration Zone Set does not need to include the road or roads you are analyzing as Origin, Middle Filter or Destination Zones in your Project. Instead, you can calibrate using data for roads near and around your study area. Note that you will get the most accurate results by calibrating with data from roads that are as close as possible to your area of interest.
Step 2: Create Projects
If you’re creating a Zone Activity Analysis, O-D Analysis, O-D with Middle Filter, O-D to Preset Geography, or Segment Analysis Project in StreetLight InSight, then you can choose between two different types of calibration:
Descriptions of the Calibration Types
2a. “None (StreetLight Index)”: Projects will run without calibration: Metrics will be provided as StreetLight Index values only. This is the default for all Project types.
2b. “Calibrate with StreetLight AADT”: StreetLight Index values will be scaled to a “Calibrated Index”, or estimated counts, using StreetLight AADT. This option uses StreetLight InSight to calculate AADT for Pass-through Zones in your Calibration Zone Sets in order to scale the StreetLight Index to estimated counts. Both the StreetLight Index and the Calibrated Index will be included in the downloads.
- This option is available for Projects with Location-Based Services with Pass-through and Navigation-GPS Data Sources.
- This option is available for Projects in the US.
- This option is available for Gold and Platinum subscriptions.
2c. “Calibrate with my Zone Counts”: StreetLight Index values will be scaled to estimated counts using Calibration Zone Sets that contain traffic count data. Both the StreetLight Index and the Calibrated Index will be included in the downloads.
This option is available for Projects with Location-Based Services with Pass-through and Navigation-GPS Data Sources.
After you have set up your project, add your calibrated Zone Set to the “Selected Calibration Zone Set(s)” box.
Note: If your Calibrated Zone Set is a unique Zone Set from the one you are analyzing in your Project, then these Zones will not go towards your total Zone Count.
Step 3: Visualize
When using Interactive Visualizations to analyze calibrated Project, you can choose to view either the StreetLight Index, Percentages, or the Calibrated Index. The “Calibrated Index” are estimated counts. Learn more about our Interactive Visualizations
Step 4: Further Analysis of the Metrics
To generate estimated counts, or “Calibrated Index values,” StreetLight InSight measures StreetLight’s trip sample in the specified calibration Zones during the Project Data Period. It then creates a ratio, or calibration factor, between the number of trips in StreetLight’s database and the count values contained in the calibration Zone Set. (Count values for the calibration Zone Set are either provided by the user or generated via StreetLight’s AADT algorithms).
StreetLight InSight then averages the calibration factors of every Zone in the calibration Zone Set. (Note: If there are more than 5 Calibration Zones, outliers are dropped.) Next, StreetLight InSight applies that average to the Metrics for the entire Project. See the table below for an example. Personal, Medium Duty Commercial (MD), and Heavy Duty Commercial (HD) vehicles are all scaled independently.
Important Information about Downloads
A few items in your downloaded Metrics will be different from Projects that are run without the Calibration Feature:
- First, you will see an additional .csv called “[Your Project_calibration_Zones.” This file includes the data you entered for each Calibration Zone. In addition, this .csv indicates the Calibration Zones that are outliers and were therefore excluded from the average calibration factor. (In the column “Personal Calibration - Is Excluded Zone,” a Y value indicates the value was excluded as an outlier).
- For each zone_traffic and od_traffic file, you will see new columns that include the Calibrated Index. As shown in the image, the column header (Zone Traffic, Origin Traffic, Destination Traffic, etc.) will be repeated. The second time it will be followed by “(Calibrated Index)”. This indicates that the StreetLight Index value was calibrated to estimate actual trip counts for the time period stated in columns G/H for this specific Project.
If you would like to analyze your Metrics in a pivot table check out this link . The only difference is this pivot table will include estimated counts instead of the StreetLight Index.
Creating a Pivot Table for Calibrated Projects
4a. First, we copied the data from the Montgomery_Calibration_1455_od_commercial.csv and Montgomery_Calibration_1455_od_personal.csv into a single tab called “downloand_data_all_pasted.”
4b. Next, we created two pivot tables.
On the tab named “pivot table O-D,” there is a classic O-D Matrix, scaled to approximate total flow between Zones. You’ll notice a few very small values. For example, on a typical weekday 1 trip gets off at exit 10b and back on at Exit 10a. This is because it’s very rare: most likely, that is someone getting off mistakenly at the wrong exit, driving around, and getting back on at the exit that was originally behind them.
The second analysis, on the tab labeled “pivot table aawdt est,” shows the change in total Zone traffic for each of the Origin Zone options. Since the 200 Eastern and Western gates comprise the entire highway, and the rest are just ramps, it’s not surprising that their volume is quite different. It is interesting that traffic volumes on the individual ramps in this section do not fluctuate with peak travel times as much as the highway overall.
If we wanted a traditional load curve with hourly bins, we would have designated one-hour day parts for all 24 hours of the day when creating the Project.