A* can be a tricky module to work with. There isn't a direct or easy way to measure the number of trips per route. However, you can get the number of time something crosses an A* node. This link to an answer by Joshua S has an example of a model that uses this node information to create a spaghetti map.
If you are interested, I believe that this would be possible using Network Nodes.
Link to Joshua S's Answer:
https://answers.flexsim.com/questions/66763/traffic-dense-visual-with-astar.html
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