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Monday, September 15, 2003
Mabey: 'Loaded' quarry trucks shouldn't use Dolores flyover
By Albert B. Lacanlale
SAN FERNANDO - "Overloaded quarry trucks should not be allowed to use the (Dolores) flyover."
David Forsyth, Mabey & Johnson Ltd. (Mabey) director general for Asia and the Pacific, made the disclosure to shed light on the apprehension of various groups in connection with the Dolores steel flyover.
Forsyth, who conducted a project presentation at the Mount Pinatubo Emergency-Project Management Office (MPE-PMO) in Barangay Sindalan, said that quarry trucks could be a threat to the integrity not only of the steel flyover, but also of other concrete flyovers and roads.
Forsyth said Mabey, which supplies steel bridging for the President's Bridge Program (PBP), loaded quarry dump trucks that are estimated to weigh beyond 42 tons -- the maximum allowable load for the steel flyover under international highway standard AASHTO HS25-44.
HS25-44, introduced in the United States in 1944, far exceeds loading limits allowed in the current Philippine highways standard, which is only HS-20.
However, Forsyth explained that the allowed load has to be spread over specified axles length (distance between the front and rear axles) of a vehicle, and not concentrated in a small area, such as on short axle length and "overloaded vehicles such as lahar trucks."
"The HS-25 code directs that for a three axle truck, the maximum allowed to be carried by one axle is 18.5 tons, and there should be at least 4.267 meters between each load," Forsyth stated.
Lifespan
He added that the "danger" presented by quarry trucks, claimed to be carrying around 37 tons of lahar, is that most of their loads are directed on one or two axles only about 1.3 meters apart.
"This means that the bridge structure can be subjected to 37 tons within a very small area and an additional 5-ton body weight in one steel span of 12 meters," Forsyth stressed.
Forsyth said that the computation did not mention tailgating of trucks and the installation of wooden expansion boards, which Mabey officials jestingly call "greedy boards".
He further explained that the steel flyover would last indefinitely if used by vehicles of loads not exceeding 42 tons and with allowable axle lengths.
However, he noted that if used by vehicles of 42 tons and over even with allowable axle lengths, then the structure would have "a limited life of 500,000 of these overweight vehicles."
If one of the 500,000 overweight vehicles were to use the flyover, Forsyth calculated that it could last up to 1,369 years. Similarly, if 100 were to pass by the flyover daily, the bridge's lifespan will drop to 13.7 years.
In the province, it was said that an average of 1,000 trucks filled with sand pass through the Dolores Junction daily.
"It is evident that the more overweight vehicles using the structure has a dramatic effect on its lifespan," Forsyth added.
Traffic reduction
Forsyth also downplayed claims that the flyover is not doing its purpose in reducing traffic congestion along the Dolores Junction.
He claimed that the flyover services 18,541 vehicles - cars, vans, jeepneys, buses, tricycles, motorbikes - of the total 25,182 vehicles taking the Eastbound and Westbound lanes of the Gapan-San Fernando-Olongapo road daily.
"That is about 72 percent reduction on vehicles taking either the Subic or the North Luzon Expressway direction since the flyover was constructed," Forsyth said.
(September 14, 2003 issue)
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