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The I-5 Widening EIS’s Incomplete Traffic Study

5:49 PM PDT on October 24, 2007

By now, it’s too late to defeat the proposed widening of the I-5 between the vicinity of SR 91 and I-605 in Los Angeles County. The Final Environmental Impact Statement, which is mercifully available in English, was released this summer, meaning the chance for the public to comment officially is over. Unofficially, it’s never too late to kill a project until the spades are in the ground.

The widening would take the current 6-lane stretch of road and widen it two more lanes in each direction. One of the given reasons to complete the project is because it will reduce carbon emissions. On page 162 (172 in your pdf file) of the EIS it says:

It should be noted that although traffic volumes are expected toincrease from their existing levels, the decrease in emission factors due toimproved technology and lower ambient levels would more than offset theincrease in CO emissions from increased traffic volumes.


However, as discussed here last week, increasing lane miles will also increase the amount of traffic on the road. The EIS/EIR for this project doesn’t take into account that the widened Route 5 will attract more traffic (and thus will create more traffic for SR 91, I-605 and the 405) than an un-widened road. The traffic study assumes that a widened I-5 will see the same increase in traffic as an-unaltered road so emissions will go down as congestion goes down.

Unfortunately, we know that not to be the case.
Decades of road widening projects across the country have proven that wider roads attract more traffic, but that knowledge has yet to find its way to an environmental study on the West Coast. The hard learned lessons of the east coast are ignored by west coast engineers, dooming us to see a repeat of their mistakes.
Again, this graphic is the actual work product of a DOT engineer in New Jersey in 2005, illustrating the reality of induced demand. Lets hope we start seeing some of that thinking here before our highway system is built out.

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