Development of Truck Payload Equivalent Factor (TPEF)
5.0 Observations
The comparison of average payloads between VIUS and VTRIS by FHWA vehicle class (Table 7 and Figures 8-16) shows that the average payload is randomly distributed among the VTRIS vehicle classes. In VIUS, vehicles are categorized based on the vehicle type specified in the questionnaire but in VTRIS the vehicles are categorized by post processing software using the distance between the axles that are recorded by WIM. Using axle distance from WIM can be problematic and subject to significant error checking for those conditions that can lead to wrong classification. For example, a car pulling a trailer may be categorized as a 3-axle truck based on the distance between axles or tailgating cars may be categorized as 4-axle truck. Non calibrated WIM can also significantly skew the actual GVW of a particular vehicle. Due to significant differences of payload between these two database, repeated analyses were carried out to ensure accuracy. No attempt was made to investigate the vehicle classification algorithm used by VTRIS and no modification was made to adjust the default empty weight reported by VTRIS for each vehicle classes. These are the few reasons for the differences in payload values between VIUS and VTRIS. The payload values from VIUS sources are higher than that from the VTRIS source and also there is a significant difference in payload value from the two sources for all the states and FHWA classes.
Comparison of the average empty weight between VTRIS and VIUS in Table 8 shows that the average empty weight for the single unit vehicles are more or less similar but for the rest of the FHWA classes, there is a significant difference in the empty weight values. The empty weight from VTRIS sources is higher than the empty weight from VIUS.
The payload distribution by product handled and GVW group for 50 states was not estimated due to the small sample size. Instead, the analysis was carried out by commodity group and FHWA class. The average payload distribution for 50 states for the FHWA class (see state specific electronic database) shows that product handling maximum payload differs for each state. Comparing the maximum payload value for each state, it can be deduced that the Utah vehicles of FHWA Class 9 transporting coal handles the maximum payload of 101,759 pounds. Observation of the national payload distribution (Table 9) shows that the vehicles of GVW Group 8 handling gasoline and aviation fuel have a maximum payload of 53,423 pounds, whereas by FHWA vehicle classification (Table 12), Class 9 vehicles handling machinery products carry a maximum payload of 104,387 pounds.
Analysis of the average payload handled by travel distance for all the states (see state specific electronic database), shows that vehicles of GVW Group 8 traveling a distance of 201 to 500 miles handle the maximum payload and of all the states, Wyoming handles the maximum payload of 60,361 pounds. The national maximum payload is 40,243 pounds for the GVW Group 8 vehicles traveling 200 – 500 miles. Analysis of the payload distribution by travel distance for the FHWA vehicle class and 50 states (see state specific electronic database) shows that the maximum average payload of 107,757 pounds is transported by combination trucks with 7 axles or more in Oregon for a distance of more than 501 miles but the national maximum average payload (Table 13) is 77,886 pounds for a trip distance of less than 50 miles.
Based on the body type, the average payload distribution for the GVW group for all 50 states shows that either the tractor + trailers: tank, bulk, or loggings of GVW Group 8 transports the maximum average payload. Analysis of payload distribution by GVW and FHWA class shows that GVW Group 8 tractor + trailers: tank vehicles of Michigan handle the maximum payload of 76,079 pounds, whereas the maximum average payload is 102,563 for the FHWA vehicle Class 9, tractor + trailers-tanks, of Michigan. The national payload distribution (Table 11) by GVW group and FHWA vehicle class shows that the national maximum average payload is 50,135 pounds for the GVW Group 8, tractor + trailers bulk vehicles and FHWA Class 9 tractor + trailers – bulk vehicles handle a maximum average payload of 83,144 pounds.
The percentage of vehicles that carry more than the weight limit or are overloaded is estimated from the cumulative gross weight graph grouped by the GVW group (Figure 18). Vehicles in the GVW Groups 2-7 in almost all states operate under the weight limit. But GVW Group 8 vehicles of all states operate over the weight limit and a maximum of 23.4% of Michigan vehicles operate over the state’s weight limit of 80,000 lbs. Considering the weight limit of 80,000 pounds, vehicles in all states operated within the weight regulation, whereas about 3% of GVW Group 2 and 8 vehicles of Vermont are overweight with a GVW of 115,000 pounds. The national cumulative gross weight graph shows that 1% of GVW Class 7 and 7% of GVW Class 8 vehicles are overweight.
The cumulative gross weight graph based on the FHWA vehicle class is shown in Figure 19. FHWA vehicle Class 6 are more predominantly overweight in most of the states. About 34% of Michigan vehicles operating under FHWA vehicle Group 6 are overweight with an average gross weight of more than 115,000 pounds. The national cumulative gross weight graph shows that about 52% of FHWA Class 6 vehicles and less than 5% of vehicles of other FHWA classes are overweight.
The percentage of overweight vehicles reported by W7 of VTRIS (Table 18) shows that the percentage is randomly distributed throughout the FHWA Class 2 - 9. Analysis shows that irrespective of the vehicle class 12% percent of vehicles are overweight in Michigan state and 70.39% is contributed by FHWA Class 9 vehicles.
