Measure M claim to reduce traffic doesn't tell the whole story

A campaign to raise the sales tax in Los Angeles County to fund billions of dollars in transportation improvements claims in TV ads that the plan will reduce traffic by 15 percent, but that's not the full story.

The ads don't explain those gains are projected 40 years into the future when traffic and population will have grown beyond current levels.

Measure M will be decided by county voters this November. It would extend a half-cent sales tax increase approved by voters in 2008 and add an additional half-cent increase forever, or until voters act to repeal them. Estimates of the cost of the tax increase for each individual in the county range from $25 to $65 annually.

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The revenues would fund massive rail expansion and highway improvements, including a subway under the Sepulveda Pass, an extension of the Gold Line to Claremont and acceleration of the Purple Line subway construction to finish in 2024, 10 years early than planned.

The Yes on M campaign has been running a series of TV ads championing the measure with the claim, "Yes on M will reduce the time you're stuck in traffic by 15 percent a day."

 
"These numbers were developed through the most conservative and credible methods," said Yusef Robb, Yes on M campaign spokesman.

The claim is based on a study commissioned by Metro as part of its Long Range Transportation Plan and conducted by Cambridge Systematics. The study projects the average hours of delay that drivers in L.A. County will experience 40 years from now. It compares a future with some population growth and no additional transportation projects to a future with population growth and 25 major projects that would be funded by Measure M.

The study says the result will be a 15 percent difference in projected traffic delay between the two alternate futures. But the claim made in the ads doesn’t fully explain that.

A chart summarizes the findings of a Cambridge Systematics modeling of future traffic delays with and without the building of projects funded by Measure M.

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LA MTA

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The projects in Measure M likely won’t reduce the current periods of times that drivers are stuck in traffic by 15 percent, but they could stop delays from getting worse by that margin by 2057.

Previous research on whether building transit or expanding highways reduces traffic delays in the short-term has shown that such construction has little effect. Last year, Metro commissioned a study by USC that showed the opening of the first phase of the Expo Line had not significantly reduced traffic along the adjacent Interstate 10 corridor or surface streets. 

Similarly, studies conducted after the $1 billion expansion of the 405 freeway showed delays during peak traffic had actually increased, although rush hour had decreased from a period of seven to five hours.

This counterintuitive reality is likely due to a phenomenon called induced demand. That's when increased capacity on roads entices more drivers to use them, thus filling them up again.

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