Minneapolis Star Tribune, MN
04-12-07
High-tech road work ahead
For drivers, new techniques in machine control will mean: Faster, more accurate
construction, roads that last longer.
By Laurie Blake, Star Tribune
Britton Lawson's bulldozer moves earth with guidance from above.
Satellite signals will guide his dozer blade along the correct angle and elevation
when he levels the roadbed for the new segment of Hwy. 36 through North St.
Paul this summer.
Minnesota is one of the first states to experiment with the use of global
positioning satellites in "machine control" construction, part of the technology
boom that is changing centuries-old road-building techniques, promising to speed
construction and produce longer- lasting roads. The Minnesota Department of
Transportation is counting on the technology to keep the high-profile Hwy. 36
project on track this summer.
"It's a huge change," said David White, a geotechnical engineer at Iowa State
University. Students there can take the nation's first college class on machine
control construction.
Using GPS signals and an onboard computer that displays a 3-D view of the
project, equipment operators "don't waste time moving material that doesn't need
to be moved," White said.
Highway will go over, under
On Hwy. 36, which requires dropping the highway under Margaret Street and
raising it over McKnight Road, the new technology will allow an efficient
exchange of dirt.
Used for years in navigation and map making, GPS has been showing up in
devices to help farmers, drivers, cyclists, backpackers, even the blind know
exactly where they are.
The use of GPS to help build roads is just beginning, but it's likely to ramp up
quickly in the next five years as its quality is confirmed, White said.
Having used GPS guidance, Lawson, who lives in Crystal, said he would never
go back to leveling roadbeds by following marks on wooden stakes pounded into
the ground by a survey team.
"I don't have to wait for a staker to come out and give me grades," Lawson said.
"You can move dirt right the first time."
Contractors are driving the shift to machine-control construction, even though the
equipment doesn't come cheap. The special features add about $60,000 to the
price of a bulldozer, and about $80,000 to the price of a compactor. In addition,
contractors must spend about $50,000 for a base receiver station, which can be
used by multiple machines.
Investment pays off
Contractors are willing to pay those costs because the machines speed up work
and cut construction costs, said Bill Hines, grading division manager for
Progressive Contractors of St. Michael.
"If I think I can do it 10 days faster than my competitor," he said. "I don't have to
put those dollars in my bid."
The capability of the new technology is "kind of unbelievable," Hines said. "In the
old days surveyors would give you cuts and fills on a piece of wood. They might
write 'Cut 3 feet,' " Hines said. "Now the machine is able to sense those cuts or
fills. It's exciting for all of us."
GPS-guided earth-moving has been in use on some highway projects in
Minnesota for several years, but the "smart roller" was first used on two state
projects last year and will be used on four more this year. The smart roller can
detect buried boulders, tires, culverts or other hazards that do not show up on
traditional surface measuring devices.
The machine uses an accelerometer, a device also used in automobile airbags
that records shock and impact. If the ground is not stiffening, the machine alerts
the operator, said Dean Potts, an engineering manager for Caterpillar Global
Paving in Brooklyn Park.
"This allows people to build with confidence. They don't have to hold up
construction waiting for an inspector," Potts said.
Machine control is not perfect, said Lou Barrett, MnDOT's transportation program
supervisor. It's best suited for big jobs that require earth moving. Tall buildings or
trees could block satellite signal reception, but making the 3-D models used by
the onboard computers adds a step to road design, she said.
MnDOT encouraged machine-control construction on Hwy. 36 through North St.
Paul this summer because it will be the first time in the metro area that a road will
be closed for construction. The experiment will scatter 40,000 daily users of the
road to alternate routes; MnDOT is watching to see how the savings in money
and construction time will balance out against the disruption created by a full
shutdown.
Equipment helped land job
Progressive Contractors landed the $27.5-million Hwy. 36 contract in part
because it has the time-saving machines, Hines said.
The International Union of Operating Engineers Local 49, based in St. Anthony,
has been training union operators in satellite-guided construction equipment for
three years to help members qualify for jobs.
"Pretty soon every piece of equipment out there is going to have a GPS on it,"
said Michael Gillson, a GPS instructor for the union. He said operators see the
benefits immediately. "I have guys that even halfway through the day say, 'I don't
know why anyone would want to do without it.' "
Laurie Blake • 612-673-1711 • lblake@startribune.com