Logic Modelling Workshop

Activities in the TRAFFIC world

The activity structure in the TRAFFIC world uses only one sort:

• Cars, which are intuitively thought of as driving along the arcs in the TRAFFIC landscape structure.

Each car has a position at each point in time. The position is indicated as a pair consisting of the segment where the car is located, and the distance travelled along the segment. The distance travelled is a number between 0 and the segment's length.

Each car has a top speed, and each road segment has a speed limit. The actual velocity of a car at each point in time is the maximum velocity allowed by the following three conditions:

• The speed limit of the road segment where it is driving
• Its own top speed
• Surrounding traffic restrictions

Cars drive at piecewise constant velocity, and can change velocity discontinuously. (A more refined variant, TRAFFIC2, will require cars to change their velocity continuously, and assumes piecewise constant acceleration/ deceleration). When a car arrives at a node ("intersection") then it may continue on any segment that connects to that node, except the one it is arriving at.

Cars can drive in both "directions" along a segment, that is, they can move both from the start node to the end node, and vice versa.

Cars can not overtake - if two cars go in the same direction on the same road segment, and one catches up with the other, then it has to stay behind at least until they arrive to the next node, where possibly the second car can choose another direction onwards. Cars going in opposite directions on the same segment can meet without difficulty, however.

The surrounding traffic restriction says that a car is never allowed to be closer than a fixed safety distance  varsigma  to the car in front of it, and it may never get itself into a situation where that could happen. This means, first of all, that when it gets to a distance of  varsigma  to a car moving in front of it on the same segment and in the same direction, then it must reduce speed to match the speed of the car in front of it. Also when getting close to a node (= an intersection), a car must reduce its speed in a way that takes into consideration all other cars that are just approaching or leaving the same node.

Maintenance information:

Latest update 21.6.1999 by EMTEK group. Edit mode aml, position code C.lmw.TRAFFIC.activities.