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Loads

Loads are the vehicle forces exerted on the pavement (e.g., by trucks, heavy machinery, airplanes). Since one of the primary functions of a pavement is load distribution, pavement design must account for expected lifetime traffic loading. Loads can be characterized by tire loads, axle and tire configurations, load repetition, traffic distribution across the pavement and vehicle speed.

H-1 freeway in Honolulu Buses in downtown Honolulu at Ala Moana
Figure 1: H-1 during rush hour. Figure 2: Buses at Ala Moana.

 

Load Characterization

Load Quantification

Pavement structural design requires a quantification of all expected loads a pavement will encounter over its design life. This quantification can be done in several ways: 

Load
Number of ESALs
18,000 lb. single axle
1.000
2,000 lb. single axle
0.0003
30,000 lb. single axle
7.9
18,000 lb. tandem axle
0.109
40,000 lb. tandem axle
2.06

Typical load equivalent factors

Figure 3: Some Typical Load Equivalency Factors

Equivalent single axle loads versus the traffic index

Figure 4: Traffic Index vs. ESALs

All approaches use the same type and quality of data but the load spectra approach has the potential to be more accurate in its load characterization.

 

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