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<br />The largest tractor-semitrailer, hence the one requir-
<br />ing the most space to maneuver, which might be encoun-
<br />tered in a particular state can be calculated using data
<br />supplied by state laws governing vehicle size and weight.
<br />
<br />A size and weight chart, prepared by the Section of
<br />State Laws, Reciprocity, and Taxation, of the American
<br />Trucking Associations, is included. It divides the country
<br />into states and regions, facilitating easy determination of
<br />necessary state size and weight laws. The chart is revised
<br />periodically to reflect changes made in the various state
<br />laws.
<br />
<br />MANEUVERABILITY DETERMINATION
<br />
<br />The turning track plot procedure described in Appen-
<br />dix I, enables one to determine (1) the dimensions of the
<br />vehicle, based on existing state laws, which will require
<br />the most space in maneuvering, and (2) that vehicle's
<br />maneuverability, by constructing turning plots showing
<br />track width generated by its width and off-track.
<br />
<br />The area a vehicle covers while maneuvering is its
<br />turning track. Basically, turning track is the result of
<br />vehicle width plus off-track generated by the vehicle in
<br />making a maneuver. (See Fig. 2, page 9).
<br />
<br />Should one be looking for general data on the space it
<br />takes to make typical maneuvers (900, 2700 turns, etc.)
<br />material is given in the various examples or on the off-
<br />tracking characteristics charts given in Appendix I on
<br />pages 30 thru 33.
<br />
<br />Space required for maneuvering is determined, with
<br />the procedure presented in Appendix I, by actually
<br />plotting track generated by the subject vehicle for the
<br />degree of turn it will be required to make. Two different
<br />methods of determining space for maneuvering are also
<br />available. They generally entail a method of determining
<br />off track, from which total track can then be calculated.
<br />
<br />Maximum off track of a particular vehicle can be cal-
<br />culated through the use of SAE J695 Turning Ability
<br />and Off tracking. 1 This method, however, does not
<br />indicate at what degree of turn the maximum off track
<br />calculated has occurred.
<br />
<br />Another procedure available, "Offtracking Calcu-
<br />lation Charts for Trailer Combinations,,,2 which was
<br />developed by Stevens, Tignor and LoJacono, and pre-
<br />sented as a paper (650721) before the SAE, enables one
<br />to calculate track for vehicles making 900 and 2700
<br />turns.
<br />
<br />J 1973 SAE HANDBOOK. Society of Automotive
<br />Engineers. Inc. 400 Commonwealth Drive. Warren dale.
<br />Pa. 15086. It should be noud thar SAE J695 was
<br />revised in the 1973 SAE Handbook. That revision con-
<br />sisud of dropping the extremely accurare and hard to
<br />
<br />VARIABLE RADIUS
<br />TURNING TRACK
<br />
<br />Turning track for a vehicle going forward and turning
<br />can be determined, then, by at least three different types
<br />of procedure. To date, however, there is no quick way to
<br />determine the turning track for a vehicle which is back-
<br />ing,or for one generally going forward but negotiating a
<br />curve using a series of forward and backing movements.
<br />The method of determining turning track presented in
<br />Appendix I can be modified to determine the paths fol-
<br />lowed in backing or in negotiating a curve by a series of
<br />forward and backward maneuvers. In backing or pro-
<br />ceeding forward around a comer by maneuvering back-
<br />ward and forward, much maneuvering is usually required
<br />and several turning track paths may be generated. A plot
<br />of one possible track generated while backing and swing-
<br />ing the semitrailer 900 is shown (see Appendix I, page
<br />28). This plot is shown to illustrate the fact the proce-
<br />dure presented can be adapted to uses other than turning
<br />track plots for vehicles proceeding forward around a
<br />comer.
<br />
<br />FLOW
<br />
<br />A factor in facility design which would be an aid to
<br />backing is, whenever possible, to make the general flow
<br />around a facility go counter.clockwise. Backing from a
<br />counter-clockwise path. the driver can more easily ob-
<br />serve and direct movement of the semitrailer. (See Fig.
<br />3, page 10).
<br />
<br />BACKING
<br />
<br />As a general rule of thumb, it is safe to assume any
<br />space that can be entered frontwards can be entered
<br />backwards. There may, however, be much more maneu-
<br />vering, hence time, required in backing. The factor gov-
<br />erning backing spaces, therefore, can be assumed to be
<br />the space which will be required for pullout.
<br />
<br />PULLOUT
<br />
<br />An area of concern, besides negotiating comers and
<br />backing, is the space required in front of a facility for
<br />pullout. A method of determining that space has been
<br />previously determined, and that method is reproduced in
<br />Appendix I on page 29. Another rule of thumb, this
<br />time for pullout, is that space required for pullout is
<br />twice vehicle length.
<br />
<br />use equation (given in Appendix I on pages 30 thru 33)
<br />. and adopting a more easily used procedure.
<br />1Hoy Stevens. Samuel C. Tignor and James F.
<br />LoJacono. "Off-tracking Calculation Charts for Trailer
<br />Combinations." SAE Technical Paper No. 650721.
<br />
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