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• Surrogate Safety Measures From Traffic Simulation Models

Surrogate Safety Measures From Traffic Simulation Models

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Alternative Text for Table 2. General simulation characteristics comparison

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Alternative Text for Table 3. Behavior modeling comparison

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Alternative Text for Table 4. Data extraction capabilities comparison.

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Alternative Text for Table 5. Calibration and parameters comparison.

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Alternative Text for Table 6. Modifications cost comparison.

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Alternative Text for Figure 1. Requirements development process.

The figure illustrates development of requirements as a process from left to right starting with cartoons of “system owner,” “users,” and “stakeholders” linked to the “objectives,” illustrated as a stack of papers. Connections between all of the entities in the figure are made with single-head arrows from left to right. The “objectives” is then connected to the “concept of operations,” illustrated as a set of interlocking gears, and the “actors,” illustrated as a smaller depiction of the interlocking gears icon and a set of three cartoon persons. The “concept of operations” and the “actors” are then connected to the “use cases,” illustrated as a set of folders. Finally, the “use cases” icon is connected to the “requirements,” illustrated as a stack of papers.

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Alternative Text for Figure 2. Event-file-based information flow diagram.

The figure shows four boxes interconnected with arrows illustrating the information flow. The first box is labeled “simulation model” and is connected to a set of boxes labeled “event files” with a single-head arrow. The event files are connected to the third box labeled “SSAM” with a single-head arrow labeled “import.” This illustrates that the SSAM interacts with the simulation model by reading the output files of the simulation model after it is finished running. A single-head arrow points right from the box labeled “SSAM” to a graphic of a table and a bar chart, illustrating that the SSAM produces graphs and charts.

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Alternative Text for Figure 3. Use case package diagram.

The figure shows five icons of folders illustrating the use case packages that are interconnected with a network of arrows indicating the connection of the packages to each other. From left to right, the use case packages are denoted "install and upgrade," "configure," "operate," "analysis," and "reports." Two stick figures are shown to illustrate the human actors "traffic engineer" and "simulation model developer." A set of interlocking gears is denoted as "simulation model" at the top of the figure to illustrate the influence of the simulation actor.

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Alternative Text for Figure 4. Main application with network-level display.

The figure shows a screen shot of a graphical user interface for the main application of SSAM. A menu bar is shown with “file,” “analysis,” “display,” “configure,” and “help” menus. A large area on the right side shows an overhead view of a traffic network. Buttons on the left side of the display allow the user to toggle layers of conflict types on the display. A highlight box on the left side shows the details of a particular conflict event. There are scroll bars for altering the portion of the screen that is in view , and a display in the lower left-hand corner of the latitude and longitude of the mouse location.

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Alternative Text for Figure 5. Intersection close-up window.

The figure shows a screen shot of a graphical user interface for the intersection close-up screen of SSAM. A large area on the right side shows an overhead view of an intersection. Buttons on the left side of the display allow the user to toggle layers of conflict types on the display and zoom in and out. A highlight box on the left side shows the details of a particular conflict event. There are drop-down boxes to select the representation of the color and shape of the icons on the display. Another drop-down box allows the user to select a particular time interval. There are scroll bars for altering the portion of the screen that is in view, and a display in the lower left-hand corner of the latitude and longitude of the mouse location.

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Alternative Text for Figure 6. Table display.

The figure shows a screen shot of a graphical user interface for a data table of SSAM. A menu bar shows “add,” “delete,” “filter,” restore,” and “save” commands. A table of sample data is shown with several columns pertaining to conflict events such as “type,” “PET,” “TTC,” etc. There are scroll bars for altering the portion of the screen that is in view.

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Alternative Text for Figure 7. Graph display.

The figure shows a screen shot of a graphical user interface for the graph display screen of SSAM. A menu bar shows “add,” “delete,” “scale,” configure,” ”restore,” and “save” commands. A sample graph is shown filling most of the screen. There are two drop-down boxes for selecting the representation of the x and y axes. There are scroll bars for altering the portion of the screen that is in view.

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Alternative Text for Figure 8. Distribution comparison display.

The figure shows a screen shot of a graphical user interface for the distribution display screen of SSAM. A menu bar shows “add,” “delete,” “select,” configure,” ”label,” and “save” commands. A sample graph is shown filling most of the screen – with two distributions shown. One distribution is shown to have a higher mean value and a different distributional shape. There are scroll bars for altering the portion of the screen that is in view.

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Alternative Text for Figure 9. Workspace display.

The figure shows a windows desktop with several open windows. One window shows a traffic simulation model user interface. Another window shows the parameters configuration screen of the traffic simulation model. Another window shows the main user interface for the SSAM with the same traffic simulation network as the traffic simulation window open in the network display. Two windows show close-up intersection graphics interfaces from the SSAM software and a third window shows a distribution comparison graphic window. The figure illustrates what a user’s desktop might look like when running analyses using the SSAM and a traffic simulation model.

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Alternative Text for Figure 10. Conflict point and lines.

The figure illustrates conflict points and lines by showing several vehicle trajectories through an intersection. The intersection is represented as a square. Conflict points are noted as dark black dots and conflict lines are shown as dark black lines where two vehicle trajectories influence each other. The mainline directions of travel are shown from left to right across the diagram and the minor traffic direction is shown from the bottom of the square. On the left, five vehicle trajectories are shown: one turning right, one progressing straight through, one changing lanes from the right lane to the left lane, one following the vehicle that turned right, and one following the vehicle that just changed lanes. From the right side, a trajectory showing a vehicle turning left and exiting the intersection to the bottom of the figure and a trajectory going straight though the intersection are shown. From the bottom of the figure, three trajectories are shown: one turning left, one turning right, and one proceeding straight across from bottom to top. Each conflict point and line is numbered 1 through 8 to show the locations where the conflicts occur.

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Alternative Text for Figure 11. Conflict point diagram.

The figure shows a graph with two vehicle trajectories. The y-axis is labeled “space” and the x-axis is labeled “time.” One vehicle trajectory is shown progressing from the bottom left corner to the upper right corner in an arcing path curving to the right. This line is labeled “through vehicle.” The second vehicle trajectory is shown from the upper left to the bottom right in an S-curve starting and ending with the trajectory being a vertical line. This line is labeled “crossing vehicle.” Both trajectories end in the y-axis at a horizontal line labeled “conflict point.” Five vertical dashed lines are shown from the x-axis to the horizontal line marked “conflict point” and are labeled “t1,” “t2,”…, “t5.”

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Alternative Text for Figure 12. Conflict line example.

The figure shows a graph with two vehicle trajectories. The y-axis is labeled “Distance to conflict point” and the x-axis is labeled “Time.” One vehicle trajectory is shown progressing from the bottom left corner to the upper right corner starting at a 45-degree angle, then curving in an arcing path to the right and then back to the left at a 45-degree angle. This line is labeled “A – Through vehicle.” The second vehicle trajectory is shown from the middle left to the upper right concave to the upper left and then a section that is at a 45-degree angle. This line is labeled “B – Turning vehicle.” Both trajectories pass across a horizontal line labeled “0” and a second line higher up on the figure labeled “Distance of follower at next time step.” Both trajectories of the leader and follower vehicles end at another horizontal dashed line further up the y-axis labeled “Reference maximum distance.” Nine vertical dashed lines are shown extending from the x-axis and are labeled “t1,” “t2,”…, “t9” and are labeled with annotations and arrows pointing to each line.

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Alternative Text for Figure 13. Rear-end conflict line example.

The figure shows a graph with two vehicle trajectories. The y-axis is labeled “Distance to conflict point” and the x-axis is labeled “time.” One vehicle trajectory is shown progressing from the upper left corner to the lower right corner starting at a 45-degree angle, then curving in an arcing path to the right. This line is labeled “Following vehicle.” The second vehicle trajectory is shown from the upper left to the lower right in a similar arcing manner below the first line. This line is labeled “Leading vehicle.” Both trajectories pass across three horizontal lines labeled “0,” “distance of follow at next time step,” and “distance of leader at road exit”, from top to bottom, respectively. The labels indicate the from the initial location. Eight vertical dashed lines are shown extending from the x-axis and are labeled “t1,” “t2,”…, “t8” and are labeled with annotations and arrows pointing to each line.

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Alternative Text for Figure 14. Surrogate measures on conflict point diagram

The figure shows the two vehicle trajectories identical to the graph in figure 11, but with additional information for the surrogate measure definitions marked on the diagram. Two triangles have been added to the curved portions of both curves for crossing and through vehicles near times t2 and t3 The filled triangles are indicated by arrows labeled “MaxS” and “DeltaS” to illustrate that the velocity is the derivative to the curve at those points. Brackets have been added between times t2-t3 and t2-t5 and are labeled TTC and PET, respectively. An arrow to the curve for the through vehicle at time t2 has been added and is labeled “initial deceleration rate.”

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Alternative Text for Figure 15.

The figure shows the two vehicle trajectories with the same information as the graph in figure 12, but with additional information for the surrogate measure definitions marked on the diagram. Four triangles have been added to the curved portions of both graphs A and B near times t2 and t4. The filled triangles are indicated by arrows labeled “MaxS and DeltaS candidates” to illustrate that the velocity of each vehicle is the derivative to the curve at those points. These values are candidates for the eventual MaxS and DeltaS values that are recorded. Brackets have been added between times t1-t4 and t3-t7 and are labeled TTC-1 and TTC-2, respectively. An arrow is pointing to TTC-1 and is labeled “Recorded TTC value” as the bracket length of TTC-1 is shorter than the bracket length of TTC-2. Brackets have been added between times t1 and the crossing of curve A at the horizontal line labeled “0” and t3 to the crossing of curve A to the horizontal line labeled “Distance of B at next time step.” The brackets are labeled PET-1 and PET-2, respectively. An arrow is pointing to PET-1 and is labeled “Recorded PET value” as the bracket length of PET-1 is shorter than the bracket length of PET-2. An arrow to curve B at time t2 has been added and is labeled “Initial deceleration rate.” Another arrow is pointing to curve B at the area where the slope is horizontal (around time t6) and is labeled “Speed zero – no longer a collision course.”

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Alternative Text for Figure 16.

The figure shows the two vehicle trajectories with the same information as the graph in figure 12, but with additional information for the surrogate measure definitions marked on the diagram. Three triangles have been added to the curved portions of both graphs A and B near times t2, t3, and t6. The filled triangles are indicated by arrows labeled “MaxS and DeltaS candidates” to illustrate that the velocity of each vehicle is the derivative to the curve at those points. These values are candidates for the eventual MaxS and DeltaS values that are recorded. Brackets have been added above curve B between times t1-t3 and t4-t5 and are labeled TTC-1 and TTC-2, respectively. An arrow is pointing to TTC-2 and is labeled “Recorded TTC value” as the bracket length of TTC-2 is shorter than the bracket length of TTC-1. Brackets have been added between times t1 and the crossing of curve B at the horizontal line and are labeled “0” and t3 to the crossing of curve B to the horizontal line labeled “10.” The brackets are labeled PET-1 and PET-2, respectively. An arrow is pointing to PET-1 and is labeled “Recorded PET value” as the bracket length of PET-1 is shorter than the bracket length of PET-2. An arrow to curve B at time t2 has been added and is labeled “Initial deceleration rate.” Another arrow is pointing to curve A at time t7 and is labeled “Leader turns off road.”

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