Design Truck recommendation for 2006, WB-40 or WB-53 3

[CEGR2004]

Working in Wilmington Delaware (Urban Condition) where I have typically used WB-40 to design truck access. While recently driving along I-95, I noticed that out of 59 trucks, not including SU's or tankers, an overwhelming portion (80%) of semi-trailer trucks were marked with the number 53'. Those semi-trailer that were not marked were smaller than the 53' so I assumed that they were wb-40's. After my unofficial truck evaluation, should I now start using wb-53' for a design truck?

 

[TerryScan]

I work in Kent & Sussex counties of Delaware. A 53' trailer is what one finds on a WB-65 vehicle. This is what DelDOT has required me to use on state road designs where a tractor trailer can be expected.

 

[ACtrafficengr]

According to the 1981 federal STAA surface transportation act, WB-65's are allowed on all "qualifying and access highways." Qualifying highways are mostly Interstates and other freeways. Access highways include all roads within 1 mile of an exit, and other roads specifically designated by the state transportation agency. Your state DOT should have a list.

In NY, WB-50s are the largest vehicle that can use roads not on the list. Delaware may be different.

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"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail."

Wm. Phelps Eno, ca. 1928

 

[TerryScan]

Thanks AC. We did usually design for WB-50. Recently I was required to use WB-65, but it probably was the nature of the specific roadway. I was not aware of the STAA list.

 

[LHA]

I don't do roadway design, so I don't know the regs, but from a practical standpoint:

I recently designed site grading and parking lot improvements to accommodate an expansion to a truck service bay at a truck stop, right of the exit ramp of I81 in PA, USA (well within the 1 mile AC refernces). The Township required, and the truck stop owners concurred, that proposed layout must accommodate a 53’ trailer and 30’ cab.

Engineering is the practice of the art of science - Steve

 

[CEGR2004]

During the course of last week I have been trying to find documentation to support my consistent use of the WB-40 as a truck design vehicle in Delaware. The precedence for using a WB-40 was set in the NCHRP Report 279, 1985 which specified truck design vehicles for the functioning highway type. The NCHRP report 505, 2003 states that trading practices resulting from the NAFTA agreement (1993) have changed the characteristics of the trucking industry. Hence, after review of this latest research, I am convinced that we should be using a WB-67 as our general truck design vehicle. Where concessions need to be made due to limiting factors, a WB-62 should be the minimum design vehicle used.



WB-67: Delaware's maximum legal trailer length = 53'
WB-62: Standard Vehicle as established under the 1982 Surface Transportation Assistance Act using a trailer lentgh = 48'

 

[TerryScan]

CEG & LHA:
I think this goes back to AC's commentary. It is somewhat site (road classification) specific. Should we use the maximum size allowed on interstates for subdivision street design?

I may try to make the design work for the infrequent moving truck of this size, but I would not be concerned with the vehicle maintaining it's own lane etc. in this situation.

For state designated Arterials and Collectors and higher classification, I would certainly design with a WB-67.

 

[LHA]

I agree, Terry. I do subdivision work, and would never design for a 53-footer to meander throughout the neighborhood...would make for fairly large cul-de-sacs

But, a service bay at a truck stop where the exit deadends into a 20' high 2:1 hillside? Yes.

Engineering is the practice of the art of science - Steve

 

[CEGR2004]

Excellent discussion, I found the dialog very helpful. I agree, interstate or arterials and maybe specific collector roads with high percentage truck traffic data, I'm going with the wb-67 based on the research. I will make the adjustment for Local Streets as required and note that larger infrequent trucks will have difficulty

FYI, excerpt from NCHRP report 505.

Several changes in the design vehicles presented in the AASHTO Policy on Geometric Design of Highways and Streets, commonly known as the Green Book, are recommended.
Specifically, it is recommended that the current WB-15 [WB-50] design vehicle be dropped because it is no longer common on U.S. roads. The kingpin-to-center-of-reartandem
(KCRT) distance for the WB-19 [WB-62] design vehicle should be increased from 12.3 to 12.5 m [40.5 to 41 ft]. The WB-20 [WB-65] design vehicle should be dropped from the Green Book and the WB-20 [WB-67] design vehicle used in its place. In addition, a three-axle truck, the SU-8 [SU-25] design vehicle, and a Rocky Mountain
Double, the WB-28D [WB-92D] design vehicle should be added to the Green Book.

 

[ACtrafficengr]

In NY, Wb-62s and WB-67s exceed legal length (65' LOA) and need a permit to go off the Qualifying and Qccess Highway network.

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"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail."

Wm. Phelps Eno, ca. 1928