Travel efficiency and traffic safety on non-signalized intersections are one of the main objectives considered in traffic management and control. Non-signalized intersections usually have more traffic conflict points than signalized ones and they are efficient if the vehicles from minor streams have a chance - a gap big enough to slip into the major stream without causing an incident or an unnecessary delay in both streams.
On non-signalized “T”, four-arm intersections or typical roundabouts, traffic flows operate as follows: the major stream has priority to cross the intersection without avoiding the minor stream. Whenever vehicles on the minor stream approach the intersection, they should at least slow down (yield sign) or stop (stop sign) and watch if an acceptable gap exists in the major stream. What is the acceptable gap at your intersection? We’ll show you how to find out from the survey data.
1. Preparation
Let’s go step by step with the analysis of traffic delay on the exemplary non-signalized roundabout. Traffic in the location below was captured using a traffic camera and the data was extracted from video footage using GoodVision Video Insights video analytics.
Picture 1: Screenshot of vehicle trajectories extracted from the video in GoodVision Video Insights platform
2. Defining the traffic movements for the analysis
In this guide, we will analyze critical gaps on the SOUTHEASTERN entry to the roundabout. The traffic movement that gives priority will be considered as a MINOR traffic stream. The MAJOR stream is the main stream of vehicles with priority, inside the roundabout.
2a) Creating a MINOR stream movement
Draw a virtual line to the place where cars from the minor stream are discharging into the roundabout. When they pass this point, it is considered that they merged with the MAJOR stream. Let’s label this line as MINOR IN respectively.
Draw another virtual line to the place, where cars are approaching the “waiting zone”. When they pass this point, it is considered that they are waiting for a gap to be accepted. Let’s label this line as MINOR WAIT respectively. The recommended distance between these two lines is approximately the length of the vehicle. Then create traffic movement for this MINOR stream. Read about defining traffic movements in Video Insights.
2b) Creating a MAJOR stream movement
Draw a virtual line to position on the major traffic stream, where cars are passing by the minor stream entry into the roundabout. This will give us very precise time-stamps of cars passing by and not giving priority to minor stream cars. Let’s label this line as MAJOR respectively. Create traffic movements for this line. Yes, the traffic movement, in this case, will be created only with one line.
See the desired configuration below:
Picture 2: Screenshot of my workspace in GoodVision Video Insights with the setup for gap acceptance analysis
3. Getting a detailed list of vehicle passages
To obtain the full list of vehicle passages on each of the movements, simply create a Vehicle List report and select these movements. Your report will be ready in a matter of seconds. Read more about vehicle list reports.
See the example below:
Picture 3: The window of the report builder in GoodVision Video Insights with selected “Vehicle List” report
A sample report is on the image below:
Picture 4: Sample of the Vehicle List report generated for the MINOR WEST movement
4. Gap-acceptance analysis
Gap acceptance analysis is fully automated in GoodVision Video Insights and the user is provided with a detailed report straight away.
Gap-acceptance analysis is always performed for each combination of MINOR and MAJOR movement. In our case, we will perform a gap-acceptance analysis report for created movements:
MINOR versus MAJOR
How to do it step by step:
Open the gap acceptance analysis reporting tool. You can download the free template from GoodVision HERE.
In the file, there are two source sheets — MINOR STREAM and MAJOR STREAM, and one results sheet called GAP ANALYSIS.
Now open the vehicle list report you generated previously. Copy and paste the required * columns (ENTRY TIME) from the MAJOR sheet of the vehicle list report to the corresponding columns of the MAJOR STREAM sheet in the Gap Acceptance Report.
Picture 5: Firstly, copy the intrusion time data from the MAJOR stream vehicle list report
4. Now copy and paste the required * columns from the MINOR sheet of the vehicle list report to corresponding columns (ENTRY TIME and EXIT TIME) of the MINOR STREAM sheet in the Gap Acceptance Report.
Picture 6: Secondly, copy the intrusion time data from the MINOR stream vehicle list report
5. All done! Now you can see the results of the gap acceptance analysis on the sheet called GAP ANALYSIS. Repeat for other roundabout entries.
Picture 7: Gap Acceptance Analysis Tool calculates gap parameters automatically, soon will be a part of GoodVision Video Insights platform
Here is the explanation of the parameters it provides:
NUMBER OF VEHICLES IN MAJOR REJECTED: This is the number of vehicles that passed through the MAJOR stream while the MINOR stream vehicle was waiting for the gap. These vehicles rejected the MINOR stream vehicle to enter the MAJOR stream.
LAST REJECTED VEHICLE PASSAGE TIMESTAMP: This is the timestamp of the last vehicle’s passage in the MAJOR stream before the gap was accepted by the MINOR stream vehicle. After this vehicle, the gap was accepted.
MAXIMUM REJECTED GAP: This is the maximum of time-gaps between MAJOR stream vehicles that rejected the MINOR stream vehicle. It is the maximum time gap that this specific MINOR stream vehicle didn’t accept.
AVERAGE REJECTED GAP: This is the average of time-gaps between MAJOR stream vehicles that rejected the MINOR stream vehicle. It is the average time gap that this specific MINOR stream vehicle didn’t accept.
ACCEPTED GAP: This is the time gap between the MAJOR stream vehicles that the MINOR stream vehicle finally accepted and entered the MAJOR stream.
CRITICAL GAP: It is the minimum of the accepted gaps in the analysis.