This guide will show you how to easily create a cut-through study using StreetLight InSight. This study provides information about the ratio of trips that start and/or end in an area versus simply traveling through it. This information can be used to explore the causes of neighborhood congestion and develop potential solutions.
To accomplish this with StreetLight InSight, you will need to create a Zone of your study area (perhaps a town, neighborhood, etc.), run an O-D Analysis using that Zone, and then download the resulting Metrics to calculate the percentages.
Step 1: Create the Zones and Zone Sets
For the cut-through study, you will create two Zones of the area you wish to study: one marked Pass-through and one not. Learn more about creating Zone Sets.
- Polygon or Line: Polygon over the area of analysis
- Pass-through: no
- Polygon or Line: Polygon over the area of analysis (copy of Zone 1)
- Pass-through: yes
For this guide, we will show the Scott’s Addition neighborhood in Richmond, VA.
First, we created the Zone Set and drew the study area. We marked one version as "no" for whether it was Pass-through, we then copied the Zone and marked it as "yes" for whether it was Pass-through.
- You may see a warning icon next to your Pass-Through Zone (as seen above). We generally recommend against large Pass-Through Zones, but for this application, the large Zone is needed.
- Be careful not to draw the Zone over any roads around the perimeter of your area of analysis. Turn on the OSM layer to be sure. When drawing any kind of Road Zone, it is important to turn on the OSM layer in the upper right-hand corner. The OSM road layer is what StreetLight InSight uses to lock trips to the underlying road network. You can choose to view the OSM layer for Vehicles, Bicycles, Pedestrians, or all three at the same time.
Step 2: Create a Project
The cut-through study is accomplished using the “O-D Analysis” Project with the same Zones as both your Origin Zone Set and Destination Zone Set. Learn more about creating an O-D Analysis.
When setting up your O-D analysis, we recommend you use "All-modes" and "Personal" for the "LBS with Pass-through" data source to capture all types of travel going through your area of analysis. Learn more about other options available.
Make sure that your Origin and Destination Zone Sets are the same.
Step 3: Interactive Visualizations
We typically recommend using Interactive Visualizations to get a quick understanding of the results. However, since the two Zones cover the same area, this analysis is best handled outside of StreetLight InSight.
Step 4: Further Analysis of the Metrics
4a. To analyze the results outside of StreetLight InSight, download them as .CSV by clicking the download button under the “All Projects” tab after the project has been run. Learn more about downloading your metrics.
4b. If you would like to compare cut-through traffic on different days and at different times, select at least the items below:
Note: If you choose to download the default options (or your Project is small) the .zip file will be delivered immediately. If you choose to download anything other than the defaults for a large Project, you may be warned that the download needs to be generated and a link to download the Project Metrics will be emailed to you.
After downloading, we highly recommend reading the README files to understand what each column in each file means.
4c. From the downloads, you can filter, create pivot tables, and use further calculations to analyze the data. Open the .CSV file that ends with “od_all.” We’ve gone ahead and hidden some columns and formatted the spreadsheet to keep things simple. We’ve also filtered by Day Type and Day Part to show only Average Weekday trips, All Day, leaving us with two rows of data.
The columns we’re most interested in are the last three: "O-D Traffic," "Origin Zone Traffic," and "Destination Zone Traffic." For the Zone not marked as Pass-through, O-D Traffic represents the amount of traffic that starts in that Origin Zone and ends in that Destination Zone. Origin Zone Traffic represents traffic that starts in that Origin, no matter where it ends. Destination Zone Traffic represents traffic that ends in that Destination, no matter where it began.
For the Zone marked as Pass-through, all three values are the same and represent the traffic that passes through the Zone. Using these values, we can calculate how much traffic starts and/or ends in the area, versus traffic that is simply passing through.
4d. For Scott's Addition, we will make a pivot table to make it quick and easy to compare cut-through ratios for different Day Types and Day Parts. Learn more about creating pivot tables.
To calculate trips that start and/or end in Scott’s Addition, we need to sum the three Traffic Indexes for the non-Pass-through Zone. However, a trip that start and ends in Scott’s Addition will be counted in all three indexes, so we need to subtract twice the O-D Index (trips that start and end in the Zone) from the sum. The formula used in the screenshot below (for cell B9) is as follows--you may need to alter it slightly to fit your project: =(C5+D5)-(2*B5). Since this is a pivot table, you’ll likely need to click the cells instead of typing them in.
No calculation is necessary for trips that simply pass through Scott’s Addition--it’s right there for us already. We’ll then sum these two numbers (B11 in the example) and calculate percentages. You can see here that for the Weekday AM Peak, 44% of trips in Scott’s Addition are cut-through. This makes sense because we know there is an interstate exit into Scott’s Addition.
4e. We also know that this neighborhood is very popular on the weekends for brewery-hopping, so we will change the filters to look at the weekend ratio as well.
Cut-through traffic reduces to only 36% on weekends.
This has been a simple way to calculate cut-through traffic in StreetLight InSight and may be all you need. However, with a more detailed project set up, perhaps an IIEE Analysis, using an Origin-Destination with Middle Filter Analysis, you can pinpoint more specifically where this cut-through traffic is coming from and where it’s going.