Sunday, July 10, 2011
Repairing Nashua's roads is a numbers game
The city's Public Works Department will pave about seven of the city's 304 miles of roads this summer, roughly one-third of the miles it needs to pave annually to keep streets from deteriorating, city engineer Stephen Dookran said.
Instead, engineers use a formula that tries to quantify street conditions to determine which ones will get paved and when.
The casual eye would say, "Do that one and that one and soon, you've got 50 miles" Dookran said. We don't have the funding for 50 miles. We don't have funding for 10 miles. The funding shortage has driven us to use a more selective option policy.
Since the division gets about $1.2 million of the $4 million it would need to keep up with needed paving, the first step to determining where to spend the money is figuring out which streets would benefit most from a fresh coat of asphalt.
Joe Mendola, a street construction engineer, and other workers survey all of the city's streets more than 5 years old and assign a number from 1-100 to the deterioration they see. That number, called the Pavement Condition Index, is part of the overall formula.
Another part is the Benefit Value. That's determined by multiplying the number of cars that use the road every day by the expected life of the repairs, 10 or 20 years, depending on whether it's a primary or secondary street.
That number is divided by the cost of the repair multiplied by the street's PCI.
Benefit is mostly to daily traffic on the street, Dookran said.
Those streets with the highest Benefit Value get paved first, Dookran said.
But that method would ignore most secondary streets that, while they don't get much daily traffic, would still be expensive to replace if the deterioration goes too far.
So, Dookran and Mendola now also put together a list of the city streets with the lowest PCI those that have the worst damage and those get repaved using any money left over once the primary streets are resurfaced.
This year, Middle Dunstable Road, Beverlee Drive and Amherst Terrace are in the worst shape. All three scored well below 30 PCI, the point that deterioration accelerates rapidly, Dookran said.
So, you really want to catch the repair before it gets too low, he said of the PCI.
Dookran said it costs two to three times as much to reconstruct a street than to repave it, so spending more on paving could save money in the long term.
The $4 million a year to pave about 20 miles a year would keep city streets at a PCI score of 51 or better, Dookran said.
A score of 51 means a street doesn't need any repair work.
Dookran said the city has used this method for close to 10 years as a way to make selecting which streets to pave more fair and standardized. But a major part of the formula depends on judgment calls regarding the conditions of streets.
We can't put too much science into this, he said. There's a lot of human interpretation that goes into it.
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