Weaving in Two Lanes

  1. First, move the "Lanes" slider so that the road is made up of exactly two lanes.

  2. Next, move the mouse cursor into the bottom lane and about 3 or 4 cm from the right edge of the road.

  3. Now click and hold down a mouse button while dragging the mouse cursor beyond and below the lower right corner of the road. Release the mouse button.

  4. A pop up menu appears. Click "top" so that a barrier along the top edge of the highlighted area is created.

  5. Now do the same to make a barrier on the left side of the road. We start by positioning the mouse cursor in the bottom lane about 3 or 4 cm from the left edge of the road.

  6. Click & hold mouse button while dragging cursor to left of and below lower left of road. Release mouse button.

  7. Again, choose "top" to create a barrier there.

The road should now look something like this:

Notice that once you created the rightmost barrier (which must extend completely to the right edge of the road) newly arriving vehicles were suddenly created in two colors. This is because by splitting the road at the right edge you create two possible destinations. Newly created vehicles are colored based on their destinations; all blue vehicles try to go to one destination, red to another, and so on, for as many destinations exist.

Lane Obstruction

Roadway obstructions like collisions or construction can be modeled as well.

  1. Use the "Lanes" slider to create a road made up of 2 or more lanes.

  2. Position the mouse cursor somewhere towards the center of the roadway.

  3. Click and hold a mouse button.

  4. Move mouse cursor so that a small rectangle is created within one lane.

  5. Release the mouse button.

  6. On the pop up menu, click "left", "top", "bottom", and (optionally) "right", so that the obstruction is created.

  7. To make the obstruction more visible, you can also decrease the speed to "1 cell/time step" using the "Max speed" slider. The slower an area's speed limit, the darker gray it is colored.

The road might now look like this:

Note the lane obstruction in the middle lane at about the center of the roadway.

On Ramp

An on-ramp is created just like the weaving setup with one change. When creating the rightmost barrier, instead of only clicking "top" be sure to click "top", "left", "right" (required!). The on-ramp will look like this:

Removing Barriers, Resetting Speed Limits

The road can be reset to its original state by highlighting the entire roadway. When the popup menu appears, click on the "Clear Area" button and then on the "Done" button. All speed limit changes and barriers have now been removed. Maximum vehicle is again 5 cells/time step everywhere on the roadway.


Not shown in the above illustrations is changing speed limits. For any rectangularly highlighted area, the speed limit slider in the popup menu can be used to adjust the max speed allowed in the region. This can be used to simulate speed changes on grades. The slower the speed limit, the darker gray the area will be drawn. (White is maximum speed.)

Here's an example where speed changes represent a crest followed by a stalled vehicle. The right end of the roadway then splits into three possible destinations. As mentioned above, vehicles are randomly assigned a destination when first created and color coded based on that destination. (Note that a destination may be comprised of more than one lane.)

Also, just about all combinations are permitted when creating barriers. Some situations, however, will illustrate shortcomings with either the CA rules or with the coding itself. As these are discovered, they are worked on.