So what’s going on here? Arguably, our mental model of traffic is just wrong. We tend to think of traffic volumes, and trip-making generally as inexorable forces of nature. The diurnal flow of 250,000 vehicles a day on an urban freeway like I-85 is just as regular and predictable as the tides. What this misses is that there’s a deep behavioral basis to travel. Human beings will shift their behavior in response to changing circumstances. If road capacity is impaired, many people can decide not to travel, change when they travel, change where they travel, or even change their mode of travel. The fact that Carmageddon almost never comes is powerful evidence of induced demand: people travel on roadways because the capacity is available for their trips, and when the capacity goes away, so does much of the trip making.
I've pointed this out before, but it bears repeating: motorists are not water molecules. Shutting down a freeway is not the same as closing a valve on a pipe and causing water to back up. Motorists make choices as to where to drive or to drive at all, and if they aware of a major closure, they will choose alternate routes to get to their destination or decide not to make the trip at all.
It's also why widening or expanding highways does nothing, in the long term, to solve traffic congestion.