Playing in traffic

Roads A and B take a roundabout route but can carry unlimited traffic. Roads a and b are shorter but subject to congestion: The more cars, the slower they go. Initially, just two routes lead from Origin to Destination: Ab and aB. Clicking on the bridge in the middle of the map opens up two more pathways: AB and ab. Will these added routes improve the flow of traffic? For more information see bit-player.org; source code on Github.
Route Count Time
Ab0--
aB0--
AB0--
ab0--
Total0--
Origin Destination A a b B
0.55
0.55
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