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Starts & Stops

Highway barriers block much more than sound

Traffic on Route 128 at a sound barrier in Lexington. A study found that concrete barriers deflect air pollution as well as sound. Traffic on Route 128 at a sound barrier in Lexington. A study found that concrete barriers deflect air pollution as well as sound. (John Blanding/ Globe Staff)
By Noah Bierman
Globe Staff / December 20, 2009

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It’s tough to think about car exhaust and eight-lane highways when you’re in a sparse Idaho desert, staring at bales of straw.

But such was the task for a group of federal research meteorologists last year who conducted a study on traffic sound barriers. Their findings, set for publication next month in the journal Atmosphere Environment, bolster the arguments of neighborhood activists who often lobby for the expensive concrete walls.

The research found that the barriers do more than protect neighbors against unwanted sounds. They also keep pollution away, reducing it by more than 50 percent on the other side of the barrier.

To simulate car fumes and other pollutants, the scientists used harmless proxy gases that are measurable at very low levels, said Dennis Finn, the lead author and a research meteorologist at the National Oceanic and Atmospheric Administration Air Resources Laboratory in Idaho Falls, Idaho.

Finn and his team set up a virtual highway in the desert, he said, using the bales of straw to simulate concrete barriers.

Then they let out the gas upwind of a barrier, sampling the air on the other side. They set up a parallel experiment without a barrier so they could compare results.

Finn said the 50 percent drop in pollution mirrored findings of other barrier tests conducted in real-world conditions. The advantage in the desert test was that he could control for such outside factors as trees and inconsistent car traffic that can affect real-world tests.

Finn said the gas released in front of the barrier gets picked up by the wind. Some hits the barrier; some goes above the barrier but disperses rather than coming down on the other side.

This sounds fairly predictable. But Finn said that some scientists had previously hypothesized that pollutants could become trapped on the other side of a barrier, where the neighbors live, because wind would be blocked and there would be nothing to disperse the fumes.

Finn lives in an Idaho town with only one highway and relatively few neighbors, so the research does not mean much to his daily life.

But what if he lived in a big city, say next to the Massachusetts Turnpike? Would he want a barrier?

“I would certainly be appreciative of it, I think, if I was living within 100 yards of a heavily traveled road,’’ he said. “A sound barrier would reduce your exposure for sure.’’

Free parking good for the short term, but costs down the road

Merchants and shoppers cheered when Boston Mayor Thomas M. Menino announced last month that he was giving away free parking during the holiday season for the 16th year in a row.

It’s become a holiday tradition - two hours at meters on Saturdays - gratis.

Who could possibly be against that, some kind of parking Grinch?

“I would rather think of myself as a parking Santa Claus,’’ said Mark Chase, a parking consultant who can explain why free parking is a really dumb idea. “You can put that as your title: ‘Parking Grinch or Santa Claus?’ You decide.’’

Chase thinks about parking all the time, mostly helping businesses and universities figure out how to avoid building more spots. Earlier this decade, when he worked for Zipcar, he designed the scheme that reserved spaces all over the city for the company cars, making the rest of us scared that the renters’ club was gearing up for some sort of military takeover of Boston and Cambridge. He is among a group of advocates and professionals who share the view, popularized in the 2005 book “The High Cost of Free Parking,’’ that parking costs need to be managed more intelligently to improve city life.

Chase says that when there is a parking shortage, giving it away free is about the worst thing you can do, for everybody. The lure of free parking draws more drivers who may have otherwise carpooled, walked, or taken public transportation. They all compete for fewer spots, driving in circles and spewing pollution in hopes of snagging one, and getting progressively angrier at the world when they don’t.

Eventually, they stop coming downtown, hurting the merchants as well.

Instead of giving it away free, charge enough for the good spots so there is always one or two of them available, he said. Charge less for the bad spots, so people will be willing to walk a little farther.

Employees usually take the free spots before shoppers, and then keep them all day anyway, he said. They got there first and many make only $7 an hour, he added.

“You can’t blame them,’’ he said.

But if you push the cheap or the free spots farther away, the employees will walk a few blocks, emptying spaces for customers.

Thomas J. Tinlin, Boston’s transportation commissioner, said the parking promotion is a gesture designed to persuade people who commute through the city to come back and shop. If they come for the promotion, maybe they’ll return the rest of the year.

It only lasts a few weeks, from late November through December 26 this year. Sundays are free year-round. Merchants have asked for more free Saturdays but the city has balked, in part because the meters raise $40,000 on average Saturdays the rest of the year.

“It’s all about balance,’’ Tinlin said.

Tinlin said parking officials are usually the ones called Grinches. Maybe with the free parking, he said, people will think of them as “good-intended elves.’’

So why does Chase one-up Tinlin, calling himself a Santa Claus? He suggests pooling all that money and then holding a holiday parking lottery.

“Give the money to one lucky customer,’’ he said.