To consolidate, disseminate, and gather information concerning the 710 expansion into our San Rafael neighborhood and into our surrounding neighborhoods. If you have an item that you would like posted on this blog, please e-mail the item to Peggy Drouet at pdrouet@earthlink.net
If you've ever found yourself stuck in traffic in your
metro area, you might want to print out the chart below, tape it to your
wall, and use it for dart practice. It comes via a guest post at the Transportationist by Wes Marshall, and it explains so very much of your earthly woe.
The
red line represents vehicle flow along a given road. Traffic steadily
rises until someone decides the road needs to be widened. Then the
original trend line (dotted red) gets replaced with an even greater
travel forecast (dotted orange), as we'd expect by creating more road
capacity. But the actual new level of travel developed by this widening
(solid red) is even greater than the forecast predicted.
In other words, widening a road invites more cars onto it. That
principle, known as "induced demand," is captured by the grey arrows
showing the gap between a travel forecast and an actual travel outcome.
Here's Marshall on the "triple convergence" of induced demand:
First, existing road users might change the time of day when they
travel; instead of leaving at 5 AM to beat traffic, the newly widened
road entices them to leave for work with everyone else. Second, those
traveling a different route might switch and drive along the newly
widened option. Third, those previously using other modes such as
transit, walking, bicycling, or even carpooling may now decide to drive
or drive alone instead.
The roots of this principle trace back to the fine work of Anthony Downs, who decades ago discovered a fundamental law of rush-hour expressway congestion. (Recent scholarship has expanded that law to include a "broad class of major urban roads" rather than just highways or expressways.) In 2004,
Downs wrote there are four ways to address the problem, but that three
of them—peak-hour tolls, greatly expand road capacity, and greatly
expand transit capacity—are "politically infeasible or physically or
financially impossible in the US."
That leaves the fourth: live with it. He writes:
Congestion is an essential mechanism for coping with excess demand
for road space. We need it! Peak-hour congestion is the balancing
mechanism that makes it possible for Americans to pursue goals they
value, such as working while others do, living in low-density
settlements, and having many choices of places to live and work.
That's not to say cities should just throw up their hands. By
creating strong transit corridors, building dense housing near these
areas, and charging a cost of driving that takes congestion into account,
the situation can and will improve. New roads can help, too, but only
for a while. Before you know it, traffic will be bad again, and local
government will need new tax revenues to maintain the extra highway
capacity that's started to crumble. Hey—watch where you're aiming that dart.
