Since driving is in decline, perhaps removing car lanes for bike lanes could free up room on space-constrained urban streets. How much more traffic could these streets serve? In spite of grumblings to the contrary, bike lanes are much more efficient at moving vehicles than traffic sewers are. (Remember that bikes are vehicles, too.) Consider first that a single road lane can typically move at most 1,000-2,000 cars per hour — the upper end for expressways and the lower end for arterials. (Local streets move fewer than 1,000.)
Removing one car lane can create enough space for two buffered bike lanes, or for one bidirectional cycletrack. Each of those lanes, in turn, could easily move almost twice as many vehicles as each car lane:
[T]he saturation ﬂow for a single 1-m (3.3 ft) to 1.2-m (4-ft) bicycle lane appears to be between 1,500 and 5,000 bicycles/hr with a majority of the observations falling between 2,000 and 3,500 bicycles/hr. (D. P. Allen, N. Rouphail, J. Hummer, J. Milazzo, TRR 1636)
In other words, converting one lane to a cycletrack can quadruple the capacity of that lane of traffic. It’s like adding three lanes of traffic, just with some paint. The inverse of that statement: even if the lane “looks” 75% less busy than the old lane of traffic, it’s still moving about as many vehicles and just about as many people (since average car occupancy is ~1.25).