STISIM Drive - Initialize Tab Box

Before a simulation run begins, STISIM Drive must set some parameters so that the program knows what to do when the driver starts. Things like vehicle position, sign position, and such must be known otherwise the software will not know what you intended for the run. The Initialize tab box allows you to set a group of parameters that will help STISIM Drive setup initialize. When you click on the Initialize tab, a dialog window similar to the following will be displayed:

When you first look at the Initialize tab box you will notice that there are 2 different groups of parameters, Startup Parameters and the Random Parameter. The Startup Parameters include a wide range of parameters that directly effect how events will be displayed on the screen. The Random Parameter is a very powerful parameter however some people have a hard time understanding how it works and why you would use it. It will be discussed in more detail a little later.

The Startup Parameters start with the "Speed limit". STISIM Drive has a resident police officer that you can selectively place in your scenario (see the PB and PE events). The police officer's sole duty is to hand out speeding tickets when the driver has exceeded the speed limit by a specified amount. The speed limit initialization parameter allows you to specify what the speed limit at the beginning of the run will be. As the run progresses this speed limit can be changed using the LS event. The speed limit is also used to determine the number of speed exceedances (times they have driven over the speed limit) that the driver has during a the run, therefore an initial value is required in order to obtain reasonable data.

Next on the parade of parameters is the "Initial lateral position". This parameter refers to the lateral position of the driver's vehicle with respect to the roadway’s dividing line, (positive to the right). This parameter allows you to specify where the vehicle will initially appear in the roadway scene and also specifies where the vehicle will be reset after a crash. For example, if you have 2 lanes in the driver''s direction you may want them to be in the first or second lane to start. This parameter allows you to place them in either one. This is an extremely important parameter when choosing the side of the road the driver will be on. If the driver will be driving on the left (such as in England, Japan, and Australia), then a negative initial lateral position will have to be used in order to place the vehicle in the correct position.

The next two parameters are very similar in that they both specify how long the driver has to react to different events. The first is the "Maximum divided attention display time" that is used in conjunction with the divided attention (DA) event. When the divided attention event is used, a symbol will be displayed on the roadway display screen. The symbol will only be displayed for the maximum time specified here. If the driver reacts before the maximum time is met, then the symbol will disappear, so this parameter only affects the DA event if the driver does not respond. In addition, this parameter is used to determine any monetary reward the driver will receive for doing well on the DA task (refer to the Post Run tab box).  The "Maximum digital input response time" is exactly like to the maximum divided attention parameter except that it acts on the digital input (DI) event.

Next in the list is the "Longitudinal offset distance at start of run" parameter. This parameter has been included to allow you to skip events in your scenario and advance to a particular spot. In most ready to go scenarios this parameter is not used, however when trying to debug a problem with one of your scenarios this parameter can be a great time saver. For example, lets say you have a 50,000 foot scenario and in the last 5,000 feet things are not working as you had hoped. Instead of driving the first 45,000 feet so that you can get to the part that needs work, you can simply set the offset distance to 45,000 feet and this is where the scenario will begin. You don't have to make any changes or delete events, just set the offset. When everything is working, set the offset back to 0 and you are ready to go.

The next parameter, "Warm up distance" has been include so that drivers can get going before they are credited with accidents. The most common occurrence that led to this parameter was drivers running off the road at the start of the run. In general they were trying to get used to the steering and pedals and would invariably not pay attention to the road and would run off it. To prevent them from being discouraged and so that they would not be penalized, this warm up no crash buffer zone has been added. If this parameter is set to 0, then the buffer is gone and they are on their own, however if you want to give them a little break, 500 to 1000 feet generally does the trick.

One of the features of STISIM drive that sets it apart from other driving simulations is its ability to keep the driver going down the course that you designed. If all of the options are setup for it, you can force the driver to drive the exact course that you had in mind. One of the reasons this is possible is because of the "Distance off road before crash occurs" parameter. This parameter sets the maximum distance, with respect to the roadway's edgeline (positive to the right), that the driver can deviate from the roadway without crashing. When the driver deviates any more than this, a crash is issued and the driver is generally reset in their lane. This means that the driver can not just drive anywhere that they want and they will have to follow the course you designed.

Another nice feature of STISIM Drive is the ability to create and display the roadway on the fly (refer to the ROAD event). However you would think this makes it difficult to place signs and signal lights because if the number of roadway lanes change, then the signs and signals will all have to be changed. Since most signs and signals are located near the edge of the roadway, STISIM Drive automatically puts them in the scene for you. All you have to do is specify where the signs are located relative to the roadway's edgeline (this is always a positive value). This is easily set using the "Sign post lateral position" parameter.

Just above we went over the warm up distance. Similar to the warm up distance is the "Crash buffer distance", however in this case it is active throughout the entire simulation run and provides a small distance after a crash where the driver is safe from other crashes occurring. Because one of the primary uses for the simulator is to place drivers in dangerous situations that you can not do in the real world, there is a tendency for them to get into multiple accidents at the same spot in the scenario. Therefore we have added a parameter to prevent this from occurring. For example there may be a group of pedestrians that are crossing the roadway, if you hit one you will be cited with a collision and if the simulator is set up to reset your position and speed, you may continue to hit pedestrians even though you are just sitting there. For that reason, the crash buffer has been instituted. When this parameter is used then for the next x feet after the collision, the driver will not be cited for another accident even if he technically has one.

Below the "Startup Parameters" is a curious and often misunderstood STISIM Drive random parameter. When you go through and create the scenario that will be displayed to the subject, you will notice that you have control over a lot of different parameters. This may be good or it may seem like an especially cruel form of torture. Some of these parameters (velocities, positions, etc.) must be specified in order for the scene to generate the type of response that you desire. Other parameters such as color might not be as critical and therefore it would be nice if the program could choose the values for you. Well, at times, it can.

First, we must consider the concept of a random value. In general, the simulation is used for research purposes and therefore data is usually collected during a simulation run. In order for the data to be correlated between runs, the drivers must be presented with the same scenario, or at least a scenario that is as close as possible. If we were to go in and completely randomize event parameters, then the chances of having drivers drive the exact same runs are very small. Therefore, STISIM Drive supports 2 different ways of producing random values. The first is a totally random value that will be different each time the simulation is run. The second produces repeatable random values based on one of the 5 options provided. The second method allows the program to choose random values for you, but ensures that the same random values will be used during each simulation run. This allows you to use random values and still have each of the drivers drive the same scenarios. Specifying the type of random values that will be used is as easy as clicking on one of the options listed.

A good example of these different random value generators would be the TREE event. When using the tree event, you must specify the maximum number of trees, their density with respect to each other, tree type, and minimum and maximum lateral positions. From this information, STISIM Drive randomly distributes trees in the display scene. If the random parameter is set to completely random, and the same events file is used for each simulation run, then the trees will always appear at different locations and at different times during the run. Setting the random parameter to one of the 5 other choices and using the same event file will produce randomly placed trees, but each subsequent simulation run will place the trees in the exact same locations.

Now that you have some idea of how STISIM Drive generates random values, the next step is to learn how to take advantage of them. In most cases, you will specify the random number when entering parameters for an event. The discussion of the parameter will inform you if the parameter can be specified randomly or not. If the parameter supports random values, then the first character in the parameter must be the * symbol. This symbol informs the program that a random number must be generated for this parameter. Additionally, you must also specify a range of numbers that will be used when selecting the random value. To specify any range of values, use the ~ symbol between the lower and upper range values. For example to specify random values between 10 and 50, you would use *10~50; values between -100 and 100 are specified as *-100~100; and so on.

In the previous paragraph, we discussed how STISIM Drive expects and interprets random inputs. During that discussion it was stated that only certain parameters of certain events will directly except random inputs. This is all well and good, but what if you want to randomize a parameter that does not allow random inputs? Well, you can’t. Actually, you can, otherwise this paragraph would not be here. The internal structure of the program makes it difficult to allow each parameter for each event to be specified randomly, therefore, you can randomize any event parameter by using the Previously Defined Event (PDE). The way this works is simple. PDEs allow you to pass parameter values to any parameter of any event in the PDE. Furthermore, PDEs have been designed to allow all passed parameters to be specified randomly. This is done exactly the same as parameters in the previous paragraph. For more information about passing random parameters or PDEs, refer to the PDE event description included in SDL.