Tutorial Saturation Flow Rate

What is Saturation Flow Rate
The saturation flow rate is the maximum hourly volume that can pass through an intersection, from a given lane or group of lanes, if that lane (or lanes) were allocated constant green over the course of an hour.

$$h_{sat}=\frac{T_{i}-T_{4}}{i-4}$$

$$SLT=T_{4} - 4h_{sat}$$

$$s=\frac{3600}{h_{sat}}$$

where,

How do we get Saturated Flow Rate in swashsim
Step1: Determine the simulation object. The object of Saturation Flow Rate simulation is an intersection. Step2: Select the intersection to be simulated. You can build the intersection you chose by yourself in swashsim or download the built products of some intersections that have been uploaded from Dr. Scott Washburn's github. (If you download the intersection from github swash17, go to step4) Step3: Model build up Step4: Simulation
 * 1) Turn on Swashsim.
 * 2) Verify the nodes that should be added into the network, input them into the “ link data” and also input the X and Y position based on landform data and the road in reality.
 * 3) Determine the percentage of vehicles turn for every direction, for example, percentage for turning right as 25%, percentage for going through is 50%, in our model this proportion is random.
 * 4) Set free flow speed (FFS), link length and curve type.
 * 5) Name the links by the node code from upstream and down-stream and fill the name in correct blank.
 * 6) Click the add lane button and build up lanes, by clicking map view button, we could have a view of the lanes we built.
 * Edit lanes by clicking right button or clicking table view in tool bar. Then set detectors on the lanes, in this project, there are 3 detectors in each straight lane on a street with 2 or more lanes in case there are vehicle lane changes. One detector is set at middle point on single lane streets.


 * The object of the project is to calculate queue length, so I set all detectors at the nearest position from stop bar. Due to the fact that the normal length of detectors is 6ft, it’s necessary to determine percentage of detector position based on length of lane in order to make sure the position is neither over the boundary of adjacent lanes nor too far from stop bar.

Step5:Data Analysis
 * The final step is to make a simulation. The warm up time is used to generate stable flow in the network and it is not contained in simulation duration. Then we set simulation duration at a number which is fewer than 3600s (1hr).
 * Swashware detector data analysis program could help with calculating saturation flow and queue length. First we should input “detector aggregate measures” file in the program and choose saturation flow option then we could click calculate button after setting desired queue length(normally 8 to 10), the program will show up saturation flow rate and saturation headway.

Verify final result
eg.,open “” in excel eg. look at queue status column，find if there are continuous queue status whose number of queuing vehicle is over 8 and under 10 eg. the first vehicle has a status of “slowing in queue”, you could count to the fourth vehicle and the last vehicle.
 * 1) Open the every link csv files by excel.
 * 1) Find if there are any continuous queue length between 8 and 10.
 * 1) In this queue, the actuation time of the fourth vehicle is T4. And the actuation time of the last vehicle in queue is Ti.
 * 1) Formula of head way and saturation flow are given in the preceding part of the text and these could be used to verify the final saturation flow.
 * 2) verify