In traffic, you have to look at both throughput and carrying capacity. Traffic jams usually result when the carrying capacity gets strained, not throughput. (The throughput of stop-and-go traffic is lower than the throughput of 70 mph traffic, but the road can carry more cars in total, so that equilibrium dominates when the load coming from surface streets exceeds some threshold.)

Without stopping and without merging. The proposal acts as if entering/exiting a tunnel at any depth is zero-cost and zero-size.