Carpool lanes, also known as HOV lanes or diamond lanes are designed as a relatively low cost solution to traffic congestion. The underlying logic is simple. If every car contained two people then we would have half as many cars on the road, and traffic congestion, the main cause of the ironically named “Rush” hour, would disappear. And while the logic is simple, the reality is less clear.
For example, in Vancouver a special HOV lane was built on one of the busiest in the city. While the number of cars with more than one rider in the morning commute increased from 600 to nearly 1,000, the number of single-occupant vehicles increased 46% to 5,200. That wasn’t foreseen. Neither was the 8% decline in bus ridership. It seems that as people began to ride-share and moved into carpool lanes, it freed up capacity in the regular lanes, encouraged more people to take the route, and because the bus riders saw only a 3 minute saving with the new lane, many of them abandoned the bus in favor of their cars.
However other cities, notably Los Angeles, have shown that HOV lanes are an important part of their strategy to reduce air pollution and shorten commute times.
Land use advocates also question the wisdom of allocating more space for more cars, pointing out that any short term gains in increased vehicle throughput is countered in short order by suburban sprawl further away from the economic centers of major cities.