The toll makes it costlier to drive into the congestion zone, which prices some car trips off the road, via "price-elasticity." With fewer cars, traffic speeds improve in the zone and en route to and from it. The time savings spur a rise in car trips to the zone. Some are trips that got priced out, others are trips that gridlock-averse drivers declined to undertake.
The initial rebound shrinks the initial time savings, leading to a drop in --- you guessed it --- rebound trips. That decrease frees up some of the road space that was gained and then lost; this bumps up the rebound trips again.
All these iterations take a lot of spreadsheet territory, ranging across the model's 14 weekday and weekend time intervals and six distinct trip types (work, non-work, through, truck, taxi, Uber), each with their own price- and time-elasticities. The whole shebang requires 40,000 equations (the entire BTA has 160,000).
I’m not diving into the happy data just yet. Why? Because there will soon be a rebound ― a bounceback in driving when traffic moves faster.
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