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AASHTO Design Vehicles

AASHTO Design Vehicles

AASHTO Design Vehicles

Does anyone know what a WB50, WB60 and WB62 really are?  What type of vehicle are they and when are they typically used?  And vice-versa, what design vehicle is typical of an automobile carrier, gasoline container truck, delivery truck to big box retail store, etc?

RE: AASHTO Design Vehicles

WB is the designation for a semitrailer vehicle (tractor and trailer).  The number that follow refer to the wheelbase, measured from the front wheels of the truck tractor to the most rear wheels of the trailer.  There are also units with double or triple trailers, desidnated with a D or T after the number.   AASHTO's green book has dimensions of various vehicles and their turning movements.  Do a web search and you'll probably be able to find the information from a variety of sources. FHWA might be a source, or your state highway department.  AASHTO does not show either tankers or automobile carriers, but I would try to design around a WB-67, which is the largest semi-trailer rig.  Delivery trucks would likely be designated as single-unit (SU) vehicle (no trailer), which has different turning dimensions than a semi-trailer.

A designer would typically use a copy of a turning movement diagram on a clear sheet to overlay the plans to check for conflicts.  There are tables which give minimum turning radii for various vehicles, but this isn't always enough to design from.

RE: AASHTO Design Vehicles

In NY state, WB 63's and larger are only allowed on a limited network of highways, so designing for them is a waste of money in most cases. NY's list of qualifying and access routes is available on the NYSDOT website, here:http://www.dot.state.ny.us/traffic/desig_hwy.html

The templates show what most vehicles in that class are capable of, with no regard for the skill (or lack of it) of the driver. It's good practice to allow at least a 3 ft (1 m) margin of error. For tandems and triples, I'd make it even more.

      "Come to think of it, there are already a million monkeys typing on a million typewriters, and the Usenet is NOTHING like Shakespeare.

       - Blair Houghton

RE: AASHTO Design Vehicles

Thanks for info from both.  Have either of you dealt with car carriers.  My client has informed that they use an 84' long car carrier.  They provided a 60.5' wheelbase, but I don't know where they measured from.  I figure it has to be a stinger-steered carrier, which I am assuming would have a smaller turning radius than a WB-62 due to the location of the pivot point.  Any input?

RE: AASHTO Design Vehicles

An 84' vehicle would need a special hauling permit in NY, so I have no experience with these. ASk your client if they can put you in contact with the vehicle manufacturer or dealer. They might have the information you are looking for.

A stinger-steered vehicle would probably off-track less than a conventional semitrailer of the same length.

      "Come to think of it, there are already a million monkeys typing on a million typewriters, and the Usenet is NOTHING like Shakespeare.

       - Blair Houghton

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