The Mackinac Straits have always been a bottleneck -- the narrow passage where Lake Michigan meets Lake Huron, where the Upper Peninsula meets the Lower, where everything that moves between them must squeeze through five miles of water. The Mackinac Bridge, built in 1957, was the physical solution: five miles of suspension bridge connecting the peninsulas. In 2200, the bridge still stands, retrofitted and reinforced, and it is the most strategically important piece of infrastructure on the eastern lake coast. The Narrows is the checkpoint that controls it.

Mackinaw City exists to process traffic across the bridge. The old tourist town -- fudge shops, Fort Michilimackinac, the boat tours to Mackinac Island -- has been subsumed into a transit security complex that makes the Gatemouth look quaint. The bridge carries the only ground route between the Lower Peninsula and the Upper Peninsula's resource extraction zones, where mining, timber, and energy production operations feed the GLMZ's industrial appetite. Every cargo vehicle, every personnel transport, every private vehicle crossing the bridge passes through the Narrows' inspection infrastructure. Ringo Systems and Axiom Industries jointly operate the checkpoint under a shared security charter -- Ringo handles personnel screening, Axiom handles cargo inspection, and both maintain armed presence on the bridge itself. The bridge towers have been fitted with sensor arrays and weapons platforms that would be alarming if anyone still had the capacity to be alarmed by such things.

The town on the south side of the bridge is a compressed version of every transit economy on the coast, intensified by the bottleneck geography. Travelers waiting for clearance fill the hotels and restaurants. Denied-transit populations accumulate in temporary camps east of town. Fixers operate the gray market in crossing papers and cargo reclassification. And above it all, visible from everywhere in town, the bridge stretches north across the Straits, its suspension cables strung with sensor nodes that blink in sequence like a nervous system made of light. On clear days you can see the Upper Peninsula's tree line. On most days the haze from the resource extraction operations obscures everything past the bridge's midpoint, and the far end disappears into industrial fog like a road into another world, which in a meaningful sense it is.