Patent Publication Number: US-8967669-B2

Title: Low floor vehicles for transporting passengers

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/827,143, entitled LOW FLOOR TRANSIT VEHICLES, filed May 24, 2013. This application is related to copending U.S. application Ser. No. 13/954,152, entitled “RETRACTABLE STEPS FOR LOW FLOOR VEHICLES FOR TRANSPORTING PASSENGERS,” filed Jul. 30, 2013. 
    
    
     BACKGROUND 
     The present specification generally relates to vehicles for transporting passengers and, more specifically, to vehicles for providing access to handicapped or ambulatory passengers. 
     Vehicles such as, for example, buses, ambulances, and the like, can be utilized to transport a relatively high volume of passengers compared to consumer vehicles such as cars. Vehicles can be produced and sold by an original equipment manufacturer (OEM). Alternatively, an OEM can manufacture and sell a chassis that includes a cab, a frame and other rolling components (e.g., drive train, axle, wheels, and the like). The OEM chassis can be sold to other manufacturers that modify the OEM chassis or add components to the OEM chassis to produce a vehicle in various states of completeness. For example, the OEM chassis can be modified by an intermediary and resold as a chassis cab that includes specialized equipment such as, for example, frame modifications and suspension modifications. An example of a chassis cab is the Air-Chassis™ by Dallas Smith Corp. of Greencastle, Ind., USA. 
     Accordingly, the OEM chassis or chassis cab can include suspension components that lower or “kneel” the chassis to a curb height to accommodate loading of passengers, frames that have been modified to accept a ramp for loading handicapped or ambulatory passengers, or both. Despite kneeling and ramp accessible chassis equipment, handicapped passengers can have difficulty with ingress and egress from low floor vehicles. 
     Accordingly, a need exists for alternative vehicles for providing access to handicapped or ambulatory passengers. 
     SUMMARY 
     In one embodiment, a vehicle for transporting passengers can include a chassis, a support member, and a labyrinthine girder. The chassis can include a front axle, a rear axle, and a frame. The rear axle can be offset from the front axle by an axle distance. The frame can support the front axle and the rear axle. The frame can include a frame rail having a recessed section and a standard section such that the frame rail spans at least a portion of the axle distance. The recessed section can be lowered compared to the standard section. The support member can be rigidly engaged to the frame rail. The support member can project from the frame rail. The labyrinthine girder can include a coupling platform that is coupled to the support member. The labyrinthine girder can form a partial enclosure that surrounds a portion of the frame rail. An offset distance can be disposed between the labyrinthine girder and the frame rail. 
     These and additional features provided by the embodiments described herein will be more fully understood in view of the following detailed description, in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments set forth in the drawings are illustrative and exemplary in nature and not intended to limit the subject matter defined by the claims. The following detailed description of the illustrative embodiments can be understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which: 
         FIG. 1  depicts a vehicle according to one or more embodiments shown and described herein; 
         FIG. 2  depicts a cross sectional view of the vehicle of  FIG. 1  according to one or more embodiments shown and described herein; 
         FIG. 3  depicts a cross sectional view of the vehicle of  FIG. 1  according to one or more embodiments shown and described herein; 
         FIGS. 4A ,  4 B, and  4 C depict a support member according to one or more embodiments shown and described herein; 
         FIGS. 5A and 5B  depict a cross sectional view of labyrinthine girders according to one or more embodiments shown and described herein; 
         FIG. 6  depicts a subfloor structure according to one or more embodiments shown and described herein; 
         FIG. 7  depicts a detail view of the vehicle of  FIG. 3  according to one or more embodiments shown and described herein; 
         FIGS. 8A and 8B  depict a subfloor structure according to one or more embodiments shown and described herein; 
         FIG. 9  depicts a retractable step according to one or more embodiments shown and described herein; 
         FIG. 10A  depicts a detailed view of the retractable step of  FIG. 9  according to one or more embodiments shown and described herein; 
         FIG. 10B  depicts a cross sectional view of the retractable step of  FIG. 9  according to one or more embodiments shown and described herein; 
         FIG. 11  depicts a cross sectional view of the subfloor structure of  FIGS. 8A and 8B  according to one or more embodiments shown and described herein; and 
         FIG. 12  depicts a detail view of the subfloor structure of  FIG. 11  according to one or more embodiments shown and described herein. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  generally depicts one embodiment of a vehicle for transporting passengers having a low floor for providing access to handicapped passengers. The vehicle generally comprises a chassis that provides the drive components and a subfloor structure for supporting specialized components of the vehicle. Various embodiments of the vehicle and the operation of the vehicle will be described in more detail herein. 
     Referring to  FIG. 1 , a vehicle  100  for transporting passengers is schematically depicted. The vehicle  100  has a chassis  10  that can be outfitted with subfloor structures  102 . The subfloor structures  102  can support or be the base structure for specialized bodies such as, for example, motor homes, fire engines, ambulances, box trucks, buses and the like. The chassis  10  comprises a front axle  12  and a rear axle  14 . The rear axle  14  can be offset from the front axle  12  by an axle distance  16 . Each of the front axle  12  and the rear axle  14  are configured to orient the wheels  18  and support the weight of the chassis  10 . The front axle  12 , the rear axle  14  or both can be configured to transmit driving torque to the wheels  18 . It is noted that, the chassis  10  can include additional components for road operation of a vehicle such as, for example, engine, transmission, driveshaft, differential, suspension, and the like. 
     Referring now to  FIG. 2 , the chassis  10  comprises a frame  20  that supports the front axle  12  and the rear axle  14 . The frame  20  is configured to provide the framework for the assembly of components to the chassis  10 . According to the embodiments described herein, the frame  20  comprises one or more frame rails  22  that span the axle distance  16  between the front axle  12  and the rear axle  14 . The frame rail  22  can be configured such that it runs along the chassis  10  in a direction that is substantially perpendicular to the front axle  12 . It is noted that, while the frame rail  22  is depicted as a single integral component, the frame rail  22  can be constructed from a plurality of members coupled to one another to traverse the any portion of the axle distance  16 . 
     The frame rail  22  comprises one or more standard sections  24  that establish a baseline height for the frame rail  22 . The frame rail  22  can further comprise a recessed section  26  that is lowered compared to the standard section  24 . For example, the recessed section  26  can be formed by modifying an existing frame by removing a portion of the frame and installing a new section at a lower height. Alternatively, a manufactured chassis can be manufactured with a section at a lower height to form the recessed section  26 . As used herein, the term “lower” and other similar directional terms generally indicate that an object is situated nearer to the ground  28 . Likewise, the term “downward” and other similar directional terms are used to indicate a direction towards the ground  28 . Additionally, as used herein, the term “higher” and other similar directional terms generally indicate that an object is situated further from the ground  28 . Likewise, the term “upward” and other similar directional terms are used to indicate a direction away from the ground  28 . It is furthermore noted that the ground  28  can be any substantially flat surface capable of supporting the chassis  10 . 
     Referring now to  FIG. 3 , the embodiments described herein can include a support member  30  for bearing loads and anchoring objects to the chassis  10 . The support member  30  can be formed from any material suitable to bear loads of objects that are anchored to the chassis  10 . Suitable materials include metals such as, for example, steel or aluminum. It is noted that the strength of the material and the size and overall number of support members  30  that may be required are inversely correlated. That is, for stronger materials, smaller and fewer support members  30  can be utilized to carry an equivalent load. While, for weaker materials, larger and more support members  30  can be utilized to carry the equivalent load. 
     Referring now to  FIGS. 4A ,  4 B and  4 C, the support member  30  can comprise frame coupling members  32  and a girder support member  34 . The frame coupling members  32  and the girder support member  34  can be formed integrally from a single plate that is bent into the desired form. Alternatively, the support member  30  can be machined out of a block of material. In some embodiments, a rounded edge  33  can be formed between each of the frame coupling members  32  and the girder support member  34 . 
     The frame coupling members  32  are configured for rigid attachment to an object. Moreover, when the frame coupling members  32  are attached to the object, the support member  30  are configured such that the girder support member  34  is offset from the object. For example, one or more of the frame coupling members  32  can comprise a notch  38 . The notch  38  can be formed such that girder support member  34  located away from and above the chassis end  40  of the frame coupling member  32 . In some embodiments, the notch  38  can comprise a substantially rectangular shape, or any other shape suitable to provide the girder support member  34  as a cantilevered support with respect to an object rigidly engaged to the frame coupling member  32 . It is noted that the phrase “rigidly engaged,” as used herein, means that objects are united, directly or indirectly, in a manner that mitigates relative motion between the objects. Accordingly, objects can be rigidly engaged via welds, bolted joints, and the like. 
     The girder support member  34  can comprise a mounting orifice  36  that is formed through the girder support member  34  to accept a fastener, such as, for example, a bolt, rod, pin, screw, and the like. The mounting orifice  36  has a length L and a height H. An aspect ratio for the mounting orifice  36  can be defined as the length L divided by the height H (H/L). In some embodiments, the mounting orifice  36  can have a substantially oval shape or substantially rectangular shape. For example, the mounting orifice  36  can be formed such that the aspect ratio is greater than about 1, in another embodiment, the aspect ratio can be from about 1.1 to about 1.8. 
     Referring still to  FIG. 4A , the free end  42  of the frame coupling member  32  can include an arched portion  48  formed downwards from and underneath the girder support member  34 . Specifically, the arched portion  48  can have a width W—measured from the chassis end  40  of the frame coupling member  32  to the free end  42  of the frame coupling member—that gradually increases as the arched portion  48  moves upwards from the lower end  44  of the support member  30  towards the upper end  46  of the support member  30 . In some embodiments, the arched portion  48  can form a substantially cubed root shape, i.e., the rate of increase of the width W can increase as the arched portion  48  moves upwards from the lower end  44  of the support member  30  towards the upper end  46  of the support member  30 . 
     Referring again to  FIG. 1 , the vehicle  100  can further comprise a labyrinthine girder  50  for supporting specialized body components over the chassis  10 . According to the embodiments described herein, the labyrinthine girder  50  is configured to provide support for a low floor, i.e., the labyrinthine girder  50  can be utilized to provide support for a floor in the vehicle  100  that is relatively close to the ground  28  when the vehicle  100  is in normal operation. The labyrinthine girder  50  can be formed from any material suitable to bear load the load of the vehicle  100  without deformation. Suitable materials include metals such as, for example, steel or aluminum. 
     Referring to  FIG. 5A , the labyrinthine girder  50  can comprise a support platform  52  for supporting structural objects. The support platform  52  can extend to a first frame bounding riser  54 . The support platform  52  can be rigidly engaged or integral with the first frame bounding riser  54  such that the first frame bounding riser  54  supports the weight of the support platform  52  and any load applied to the support platform  52 . The interface between the support platform  52  and the first frame bounding riser  54  can form a first girder angle α 1 . 
     The labyrinthine girder  50  can further comprise a frame bounding platform  56  and a second frame bounding riser  58 . The first frame bounding riser  54 , the frame bounding platform  56  and the second frame bounding riser  58  can cooperate to form a partial enclosure  64 . Specifically, the first frame bounding riser  54  and the second frame bounding riser  58  can be oriented to extend substantially vertically, i.e., upwards and downwards. The first frame bounding riser  54  and the second frame bounding riser  58  can be spaced from one another. The frame bounding platform  56  can span the space between the first frame bounding riser  54  and the second frame bounding riser  58  and can be rigidly engaged or integral with each of the first frame bounding riser  54  and the second frame bounding riser  58  to demarcate the partial enclosure  64 . The interface between the first frame bounding riser  54  and the frame bounding platform  56  can form a second girder angle α 2 . The frame bounding platform  56  and the second frame bounding riser  58  can form a third girder angle α 3 . 
     According to the embodiments described herein, the labyrinthine girder  50  can comprise a coupling platform  60  for mounting the labyrinthine girder  50  to an object. The coupling platform  60  can be rigidly engaged or integral with the second frame bounding riser  58  such that when the coupling platform  60  is coupled to an object, the coupling platform  60  supports the weight of the labyrinthine girder  50  and any load applied to the labyrinthine girder  50 . The interface between the coupling platform  60  and the second frame bounding riser  58  can form a fourth girder angle α 4 . 
     The labyrinthine girder  50  can also comprise a support bounding riser  62  that forms a flange for containing an object mounted to the labyrinthine girder  50 . The support bounding riser  62  can be rigidly engaged or integral with the coupling platform  60 . The interface between the coupling platform  60  and support bounding riser  62  can form a fifth girder angle α 5 . It is noted that, while the fifth girder angle α 5  is depicted in  FIG. 5A  as being about 90°, the fifth girder angle α 5  can be any angle that is sufficient to orient the support bounding riser  62  to the coupling platform  60  such that the support bounding riser  62  operates as a secondary retention feature for an object coupled directly or indirectly to the labyrinthine girder  50 . For example, in one embodiment the fifth girder angle α 5  can be from about 60° to about 120°. 
     Referring collectively to  FIGS. 5A and 5B , the labyrinthine girder  50  ( FIG. 5A ) and the labyrinthine girder  150  ( FIG. 5B ), which is similar in structure to the labyrinthine girder  50  with the omission of the support bounding riser  62 , can have a substantially top hat shape. Specifically, the support platform  52 , the first frame bounding riser  54 , the frame bounding platform  56 , the second frame bounding riser  58 , and the coupling platform  60  can cooperate to form a cross sectional shape that follows a substantially top hat shape. It is noted that, while the first girder angle α 1 , the second girder angle α 2 , the third girder angle α 3 , and the fourth girder angle α 4  are depicted as having substantially the same angle, each of the first girder angle α 1 , the second girder angle α 2 , the third girder angle α 3 , and the fourth girder angle α 4  can have their own distinct angle without deviating from the top hat shape. It is furthermore noted that, while the first girder angle α 1 , the second girder angle α 2 , the third girder angle α 3 , and the fourth girder angle α 4  are depicted as being about 90°, according to the embodiments described herein, the first girder angle α 1 , the second girder angle α 2 , the third girder angle α 3 , and the fourth girder angle α 4  can be any angle from about 45° to about 135°. 
     Moreover, the top hat shape can be formed from a variety of configurations that provide the support platform  52 , the frame bounding platform  56 , and the coupling platform  60  for supporting loads from an object coupled to the coupling platform  60 , while contemporaneously defining the partial enclosure  64 . Accordingly, additional facets and features can be added to the embodiments described herein without deviating from the substantially top hat cross sectional shape. It is furthermore contemplated that facets and features can be removed from the embodiments described herein without deviating from the top hat shape, provided that shape includes the aforementioned load support characteristics and partial enclosure  64 . 
     Referring again to  FIG. 1 , the vehicle  100  can comprise a subfloor structure  102  that mounts to the chassis  10  and provides support for flooring surfaces to be mounted upwards of the subfloor structure  102 . According to the embodiments described herein, the subfloor structure  102  can define a plurality of sections. The subfloor structure  102  can comprise an access ramp frame  70  for providing ingress and egress from the vehicle  100 , a passenger section  106  for providing seating for passengers during transit, a landing section  108  for providing a substantially level surface for securing passengers seated within wheel chairs, and an elevated passenger section  110  for providing additional seating for passengers during transit. 
     Referring collectively to  FIGS. 1 and 6 , embodiments of the present disclosure can comprise an access ramp frame  70  for providing structural support for an entrance ramp. Accordingly, the access ramp frame  70  generally includes structural members that are rigidly engaged or integral with one another to form a structure suitable for handling the loads generated during the loading and unloading of passengers. The access ramp frame  70  can be formed from metals such as, for example, steel or aluminum. 
     The access ramp frame  70  has a lowered end  72  that is located near an outer boundary of the vehicle and a raised end  74  that is higher in elevation than the lowered end  72 . Generally, the access ramp frame  70  forms the base for the installation for an inclined surface that has a gradually increasing slope from the lowered end  72  to the raised end  74  of the access ramp frame  70 . The access ramp frame  70  can comprise a lower cross member  76  at the lowered end  72  of the access ramp frame  70  and extending across the access ramp frame  70 , and an upper cross member  78  at the raised end of the access ramp frame  70  and extending across the access ramp frame  70 . The access ramp frame  70  can comprise an intermediate cross member  80  located between the lower cross member  76  and the upper cross member  78 , and extending across the access ramp frame  70 . 
     Additionally, the access ramp frame  70  can comprise a first ramp support member  82  and a second ramp support member  84  located across the access ramp frame  70  from one another. Each of the first ramp support member  82  and the second ramp support member  84  can extend from the lower cross member  76  to the intermediate cross member  80 . Each of the first ramp support member  82  and the second ramp support member  84  can form a slope as each gradually increases in elevation between the lower cross member  76  and the intermediate cross member  80 . 
     The access ramp frame  70  may further comprise a first intermediate ramp support member  86  and a second intermediate ramp support member  88  located across the access ramp frame  70  from one another. Each of the first intermediate ramp support member  86  and the second intermediate ramp support member  88  can extend from the intermediate cross member  80  to the upper cross member  78 . Each of the first intermediate ramp support member  86  and the second intermediate ramp support member  88  can form a slope as each gradually increases in elevation between the intermediate cross member  80  and the upper cross member  78 . In some embodiments, the first intermediate ramp support member  86  and the second intermediate ramp support member  88  can each be shorter in length, i.e., the distance between the intermediate cross member  80  and the upper cross member  78 , than of the length each of the first ramp support member  82  and the second ramp support member  84 , i.e., the distance between the lower cross member  76  and the intermediate cross member  80 . It is noted that, according to the embodiments described herein, components can be added to or deleted from the access ramp frame  70 . 
     Referring collectively to  FIGS. 1 and 6 , the passenger section  106  can comprise a labyrinthine girder  50  and a second labyrinthine girder  250 . Each of the labyrinthine girder  50  and the second labyrinthine girder  250  can be of substantially similar construction, as is described hereinabove in greater detail. The labyrinthine girder  50  and the second labyrinthine girder  250  can be aligned with on another such that the labyrinthine girder  50  and the second labyrinthine girder  250  are substantially parallel. Additionally, it is noted that, while the coupling platform  60  of the labyrinthine girder  50  and the second labyrinthine girder  250  are depicted as facing one another, i.e., towards the center of the passenger section  106 , the coupling platform  60  of the labyrinthine girder  50  can face the support platform  52  of the second labyrinthine girder  250 , and vice versa. 
     The subfloor structure  102  can further comprise a loading side support  90  and a landing side support  92  that are located on opposing sides of the subfloor structure  102  and run along the length of the subfloor structure  102 , i.e., substantially along the axle distance  16 . The subfloor structure  102  can further comprise joists  94  for providing mounting points and structural support in a direction substantially perpendicular to the axle distance  16  for the flooring surfaces. Spacers  96  and structural plates  98  can be further utilized to provide additional mounting points for flooring surfaces and accessories such as, for example, seats, hand rails and the like. Each of the loading side support  90 , the landing side support  92 , joists  94 , spacers  96  and structural plates  98  can be formed from the materials described herein above with respect to the labyrinthine girder  50 . 
     Referring collectively to  FIGS. 1 and 3 , one or more joists  94  can extend from the loading side support  90  to the labyrinthine girder  50 . For example, a first end of each of the joists  94  can be rigidly engaged with the loading side support  90  and a second end of each of the joists  94  can be rigidly engaged with the coupling platform  60  of the labyrinthine girder  50 . Additionally, one or more structural plates  98  can be rigidly engaged with the loading side support  90 . 
     One or more joists  94  can extend from the labyrinthine girder  50  to the third labyrinthine girder  350 . Specifically, a first end of each of the joists  94  can be rigidly engaged with the support platform  52  of the labyrinthine girder  50  and a second end of each of the joists  94  can be rigidly engaged with the support platform  52  of the third labyrinthine girder  350 . Spacers  96  and structural plates  98  can be rigidly engaged with the support platform  52  of each of the labyrinthine girder  50  and the third labyrinthine girder  350 . 
     The passenger section  106  of the subfloor structure  102  can further comprise one or more joists  94  that extend from the second labyrinthine girder  250  to the landing side support  92 . Specifically, a first end of each of the joists  94  can be rigidly engaged with the coupling platform  60  of the second labyrinthine girder  250  and a second end of each of the joists  94  can be rigidly engaged with the landing side support  92 . Additionally, one or more structural plates  98  can be rigidly engaged with the landing side support  92 . A top surface of each of the joists  94 , spacers  96  and structural plates  98  of the passenger section  106  can be substantially flush to provide mounting points for flooring sheets. 
     Referring collectively to  FIGS. 1 and 3 , the passenger section  106  of the subfloor structure  102  can be rigidly engaged with the access ramp frame  70 . The rigid engagement can be formed adjacent to the recessed section  26  of the chassis  10 . Specifically, the raised end  74  of the access ramp frame  70  can be rigidly engaged with an end of the labyrinthine girder  50  that terminates above the recessed section  26  of the chassis  10 . In some embodiments, the first ramp support member  82 , the intermediate cross member  80 , or both can be rigidly engaged with the labyrinthine girder  50 . The access ramp frame  70  can be coupled with the labyrinthine girder  50  via supports such as, for example, brackets, braces, ties, and the like. Alternatively, or additionally, the access ramp frame  70  can be in direct contact with the labyrinthine girder  50 . 
     Referring collectively to  FIGS. 3 and 7 , the labyrinthine girder  50  can be capped at the end above the recessed section  26  of the chassis  10  to provide additional strength to the rigid engagement of the access ramp frame  70  and the labyrinthine girder  50 . Specifically, the labyrinthine girder  50  can be rigidly engaged with a ramp support plate  114  that fills at least a portion of the partial enclosure  64  of the labyrinthine girder  50 . The ramp support plate  114  can be formed from material similar to the labyrinthine girder  50  to provide an additional mounting surface for the access ramp frame  70 . In some embodiments, the ramp support plate  114  can follow the contour of the support bounding riser  62 , the coupling platform  60 , the second frame bounding riser  58 , the frame bounding platform  56 , and the first frame bounding riser  54  and extend downwards from the labyrinthine girder  50  towards the recessed section  26  of the chassis  10 . It is noted that the ramp support plate  114  can be formed in any shape suitable to fill at least a portion of the partial enclosure  64  while providing additional strength to the rigid engagement between the labyrinthine girder  50  and the access ramp frame  70 . 
     Referring collectively to  FIGS. 1 and 6 , the landing section  108  of the subfloor structure  102  can comprise a third labyrinthine girder  350  that extends from the second labyrinthine girder  250  towards the front axle  12  of the chassis  10 . The third labyrinthine girder  350  can be of substantially similar construction as the labyrinthine girder  50 , described hereinabove. One or more joists  94  can extend from the raised end  74  of the access ramp frame  70  to third labyrinthine girder  350 . For example, a first end of the one or more joists  94  can be rigidly engaged with the upper cross member  78  of the access ramp frame and a second end of the one or more joists  94  can be rigidly engaged with the support platform  52  of the third labyrinthine girder  350 . Additionally, spacers  96  can be rigidly engaged with the support platform  52 , the coupling platform  60  of third labyrinthine girder  350 , or both. One or more joists  94  can extend from the third labyrinthine girder  350  to the loading side support  90 . For example, a first end of the one or more joists  94  can be rigidly engaged with the coupling platform  60  of third labyrinthine girder  350  and a second end of the one or more joists  94  can be rigidly engaged with the landing side support  92 . Additionally, structural plates  98  can be rigidly engaged with the landing side support  92 . 
     The landing section  108  of the subfloor structure  102  can further comprise a transition member  112  that extends from the raised end  74  of the access ramp frame  70  to the third labyrinthine girder  350 . Accordingly, the transition member  112  can span any changes in elevation between the raised end  74  of the access ramp frame  70  and the third labyrinthine girder  350  to provide mounting surfaces and structural rigidity. In some embodiments, a first side of the transition member  112  can be rigidly engaged with the upper cross member  78  of the access ramp frame  70  and a second side of the transition member  112  can be rigidly engaged with the support platform  52  of the third labyrinthine girder  350 . Accordingly, when the first side of the transition member  112  or the upper cross member  78  of the access ramp frame  70  is not substantially flush with the one or more joists  94  of the landing section  108  of the subfloor structure  102 , the transition member  112  can gradually accommodate the elevation change such that the second side of the transition member  112  is substantially flush with the one or more joists  94  of the landing section  108  of the subfloor structure  102 . 
     In addition to being rigidly engaged with both the access ramp frame  70  and the third labyrinthine girder  350 , the transition member  112  can be rigidly engaged with the chassis  10  such as, for example, the portion of the chassis  10  immediately forward of the transition member  112 . The transition member  112 , as noted above, can be utilized as a structural component. Accordingly, the transition member  112  can be formed from a metal such as, for example, aluminum, steel, and the like. In some embodiments, the transition member  112  can be a desired length of angle iron. A top surface of each of the joists  94 , spacers  96 , structural plates  98 , and transition member  112  of the landing section  108  can be substantially flush to provide mounting points for flooring sheets. 
     Referring again to  FIGS. 1 and 2 , the subfloor structure  102  can comprise an elevated passenger section  110  that is elevated with respect to the passenger section  106  to provide clearance for the rear axle  14  of the chassis  10 . For example, the frame rail  22  of the chassis  10  can be formed with a raised section  27  adjacent to the rear axle  14 . Accordingly, the elevated passenger section  110  can be formed from structural members that are configured to provide clearance between the subfloor structure  102  and the rear axle  14  during normal operation of the rear axle  14 . In some embodiments, the boundary between the passenger section  106  and the elevated passenger section  110  can be delineated by a subfloor discontinuity  116 , i.e., a more rapid change in elevation can occur at the subfloor discontinuity  116  that at the passenger section  106  or the elevated passenger section  110 . Accordingly, a majority of the elevation change between the passenger section  106  and the elevated passenger section  110  can be consumed at the subfloor discontinuity  116 , which can provide for a substantially flat passenger section  106  and landing section  108 . The subfloor discontinuity  116  can be utilized as a step in the vehicle  100 . Alternatively or additionally, a ramp can be utilized to provide access to the elevated passenger section  110  via the subfloor discontinuity  116 . 
     Referring now to  FIGS. 8A and 8B , the embodiments described herein can comprise a retractable step  120  that can articulate automatically between a step position ( FIG. 8A ) and a ramp position ( FIG. 8B ). The retractable step  120  can comprise an articulating tread  122  that can be utilized both as a tread of a step when the retractable step  120  is in the step position and a ramp when the retractable step  120  is in the ramp position. The retractable step  120  can further comprise a riser door  124  that articulates and interacts with the retractable step  120  to transition between the step position and the ramp position. 
     Referring now to  FIG. 9 , which depicts the retractable step  120  in a maintenance position, the retractable step  120  can comprise a ramp housing  130  that can be mounted to structural members and provide a support structure for the retractable step  120 . In some embodiments, the ramp housing  130  can be formed in a substantially box shaped enclosure having sidewalls  132  and a back wall  134  that are rigidly engaged or integral with a base  136 . The riser door  124  can be in rotatable engagement with the ramp housing  130  such that riser door  124  can rotate into and out of the interior  131  of the ramp housing  130 . For the purpose of defining and describing the present disclosure, the phrase “rotatable engagement,” as used herein, means that an object is directly or indirectly attached to another object in a manner that allows the object to swing around an axis. Accordingly, a rotatable engagement can include one or more hinges, pins, ball-socket joints, and the like. 
     The articulating tread  122  can be in rotatable engagement with the ramp housing  130  such that the articulating tread  122  can rotate into and out of the interior  131  of the ramp housing  130 . In some embodiments, the articulating tread  122  can be in rotatable engagement with the back wall  134  of the ramp housing  130 . As is noted hereinabove, the articulating tread  122  and the riser door  124  can cooperate to transition between the step position ( FIG. 8A ) and the ramp position ( FIG. 8B ). Accordingly, the articulating tread  122  and the riser door  124  can include components and features to facilitate cooperative motion. In some embodiments, the riser door  124  can be rigidly engaged with a light that is configured to illuminate at least a portion of the passenger section  106 . The light can be any device capable of projecting optical signals such as, for example, an incandescent, a light emitting diode, a laser, and the like. 
     Referring collectively to  FIGS. 9 and 10A , the articulating tread  122  can comprise a slide interface  160  for facilitating cooperative motion with the riser door  124 . The slide interface  160  can be a substantially smooth surface located on the underside of the articulating tread  122 . Additionally, the articulating tread  122  can comprise a block engagement feature  162  for temporarily retaining the riser door  124 , when the retractable step  120  is in the step position ( FIG. 8A ). Accordingly, the block engagement feature  162  can be formed into any shape suitable to clasp or engage a portion of the riser door  124 . For example, the block engagement feature  162  can be formed into a rounded corner, substantially semi-circular shape, or any other shape suitable to clasp a portion of the riser door  124 . In some embodiments, the block engagement feature  162  can be formed at the free end of the articulating tread  122 . 
     The retractable step  120  can comprise one or more angled support walls  164  for providing structural support to the articulating tread  122 , when the retractable step  120  is in the ramp position ( FIG. 8B ). The one or more angled support walls  164  can be rigidly engaged with or integral to the articulating tread  122 . In some embodiments, the retractable step  120  can comprise an angled support wall  164  on opposing sides of the articulating tread  122  adjacent to the sidewalls  132  of the ramp housing  130 . The angled support walls  164  can be angled such that, when the retractable step  120  is in the ramp position ( FIG. 8B ), at least a portion of the one or more angled support walls  164  is in contact with the base  136  of the ramp housing  130 . Accordingly, the one or more angled support walls  164  can bear loads applied to the articulating tread  122  and transfer at least a portion of the load to the base  136  of the ramp housing  130 . 
     Each of the one or more angled support walls  164  can comprise a riser clearance feature  166  that cooperates with the riser door  124  to allow the angled support wall  164  to contact the base  136  of the ramp housing  130 , when the retractable step  120  is in the ramp position ( FIG. 8B ). In some embodiments, the riser clearance feature  166  can be a profiled edge that matches the cross sectional shape of the riser door  124 . Accordingly, when the retractable step  120  is in the ramp position ( FIG. 8B ), the riser clearance feature  166  can contact the angled support wall  164 , while a portion of the angled support wall  164  is in contact with the base  136  of the ramp housing  130 . In further embodiments, the riser clearance feature  166  can be a profiled edge that is oversized compared to the cross sectional shape of the riser door  124 . Thus, when the retractable step  120  is in the ramp position ( FIG. 8B ), the riser clearance feature  166  can be offset from the angled support wall  164 , while a portion of the angled support wall  164  is in contact with the base  136  of the ramp housing  130 . 
     Referring again to  FIG. 9 , the riser door  124  can comprise one or more slide blocks  142  that cooperate with the articulating tread  122  to allow the retractable step  120  to transition between the step position ( FIG. 8A ) and the ramp position ( FIG. 8B ). For example, the one or more slide blocks  142  can slide across the slide interface  160  of the articulating tread  122  as the retractable step  120  transitions between the step position ( FIG. 8A ) and the ramp position ( FIG. 8B ). Accordingly, the one or more slide blocks  142  can be formed from any material that is resistant to fatigue and has a relatively low coefficient of friction such as, for example, polypropylene. Moreover, it is noted that alternative materials can be utilized and may include lubricants, rolling mechanisms, and the like. 
     Additionally, the one or more slide blocks  142  can support the articulating tread  122 , when the retractable step  120  is in the step position ( FIG. 8A ). Specifically, the one or more slide blocks  142  can be shaped to apply a force within the block engagement feature  162  of the articulating tread  122 , when the retractable step  120  is in the step position ( FIG. 8A ). Accordingly, the one or more slide blocks  142  can be formed to substantially match the profile of the block engagement feature  162 . 
     The retractable step  120  can comprise an actuator  140  for driving the motion of the retractable step  120 , holding the retractable step  120  in a fixed position, or both. The actuator  140  can be any mechanical system, electrical system, pneumatic system, hydraulic system or combination thereof capable of driving the retractable step  120 . In some embodiments, it may be preferred to utilize a pneumatic actuator or electrical motor as the actuator  140  in order to provide greater reliability and cleanliness during operation. The actuator  140  can provide linear or rotational actuation to drive the rotation of the articulating tread  122 . 
     Referring collectively to  FIGS. 9 and 10B , the actuator  140  can be in rotatable engagement with the riser door  124  and rigidly engaged with the ramp housing  130 . In some embodiments, the ramp housing  130  of the retractable step  120  can comprise an actuator cavity  138  for aligning a linear actuation of the actuator  140  with the riser door  124 . The actuator cavity  138  can extend downward from the base  136  of the ramp housing  130  and increase the volume of the interior  131  of the ramp housing  130 . The actuator cavity  138  can comprise a back face  170  and an inclined face  172  that aligned with one another at an angle of incline β. In some embodiments, the angle of incline β can be acute. When the actuator  140  is a linear actuator, the linear actuation can be provided at an angle with respect to the riser door  124  that is less than or equal to the angle of incline β. Accordingly, the actuator  140  can be rigidly engaged within the actuator cavity  138  in substantial alignment with the back face  170 . For example, the actuator  140  can be rigidly engaged with the back face  170 , the inclined face  172 , or both. 
     The ramp housing  130  of the retractable step  120  can further comprise one or more inclined towers  144  for providing additional clearance for chassis components such as, for example, suspension and axle components. The one or more inclined towers  144  can extend upward from the base  136  of the ramp housing  130  and decrease the volume of the interior  131  of the ramp housing  130 . The one or more inclined towers  144  can be shaped to provide clearance for the articulating tread  122 , when the retractable step  120  is in the ramp position ( FIG. 8B ). In some embodiments, the one or more inclined towers  144  can be shaped to contact and provide structural support for the articulating tread  122 , when the retractable step  120  is in the ramp position ( FIG. 8B ). Additionally, the ramp housing  130  can comprise a prop bar  146  that is in rotatable engagement with the base  136  of the ramp housing  130  at a first end and configured to support the tread in the maintenance position ( FIG. 8 ) at a second end. 
     Referring now to  FIG. 11 , the subfloor structure  102  an be rigidly engaged with the chassis  10  to provide support for interior components such as, for example, flooring sheets, carpeting, padding, seating, and the like. In some embodiments, the subfloor structure can be rigidly engaged with the chassis  10  such that an offset distance D is maintained between the frame rail  22  and the labyrinthine girder  50  and the frame rail  22  and the third labyrinthine girder  350 . The offset distance D is any distance suitable to maintain a clearance between the frame rail  22  and the labyrinthine girder  50  and the frame rail  22  and the third labyrinthine girder  350  during normal operation of the vehicle  100 . 
     Referring collectively to  FIGS. 4A ,  11  and  12 , the subfloor structure  102  can comprise one or more support members  30  rigidly engaged with the frame rails  22  of the chassis  10 . Specifically, the chassis end of the frame coupling member  32  of the support member  30  can be rigidly engaged with the frame rail  22 . The support member  30  can project away from the frame rail  22  and the notch  38  can form a cavity adjacent to the frame rail  22 . Accordingly, the girder support member  34  can be cantilevered from the frame rail  22  and provided as a mount for the third labyrinthine girder  350 . It is noted that, while description is provided regarding mounting the third labyrinthine girder  350  to the one or more support members  30 , the labyrinthine girder  50  and the second labyrinthine girder  250  can be mounted to the one or more support members  30  in a manner similar to the third labyrinthine girder  350 . 
     Referring collectively to  FIGS. 11 and 12 , the subfloor structure  102  can further comprise a vibration isolator  180  for mitigating relative downward motion of the subfloor structure  102  with respect to the frame rail  22 . The vibration isolator  180  can be formed from any material exhibiting viscoelastic properties including, but not limited to, polymers such as, for example, rubber, polyurethane, and the like. In some embodiments, the vibration isolator  180  can be formed in a substantially cylindrical shape having a through hole in the center. The vibration isolator  180  can be located between the girder support member  34  of the support member  30  and the coupling platform  60  of the third labyrinthine girder  350 . 
     In some embodiments, the subfloor structure  102  can further comprise an additional vibration isolator  182  for mitigating relative upward motion of the subfloor structure  102  with respect to the frame rail  22 . For example, the additional vibration isolator  182  can be located beneath the vibration isolator  180  with the girder support member  34  of the support member  30  located between the additional vibration isolator  182  and the vibration isolator  180 . The coupling platform  60  of the third labyrinthine girder  350  can be fastened to the vibration isolator  180 , the support member  30 , and the additional vibration isolator  182  with a fastener  184 . As used herein, the term “fastener” means a device for enclosing objects together to limit the motion of the objects with respect to one another such as, for example, a bolt, a crew, a pin, a rivet, a rod, and the like. The pitch of the second labyrinthine girder  250  from front to back can be adjusted by varying the height of the vibration isolator  180 , by varying the elevation of the support members  30 , or a combination thereof. 
     Referring collectively to  FIGS. 8A ,  8 B and  11 , the subfloor structure  102  can further comprise one or more subfloor sheets  174  for providing a substantially flat surface for the interior components (e.g., carpeting, padding, seating, etc.) of the vehicle  100 . The subfloor sheets  174  can be a single layer of material or can be composed of multiple layers of one or more materials. In some embodiments, the subfloor sheets  174  can be flush with the frame bounding platform  56  of the labyrinthine girder  50 , the second labyrinthine girder  250 , the third labyrinthine girder  350 , or combinations thereof. Specifically, the thickness of the subfloor sheet  174  can be set such that when the subfloor sheet  174  lays upon a component of the subfloor structure  102  such as, for example, a joist  94 , a spacer  96  ( FIG. 1 ), or a structural plate  98  ( FIG. 1 ), the subfloor sheet  174  is flush with the frame bounding platform  56 . 
     It should now be understood that the embodiments described herein can provide access to the interior of a vehicle for passengers that require the use of assistive devices such as, for example, walkers or wheelchairs. Specifically, the subfloor structures described herein can provide a plurality of sections that can form interior sections of substantially flat and substantially level surfaces for the ingress and egress of passengers using assistive devices. 
     Specifically, the vehicle can be provided with a suspension system that kneels the vehicle to curb height such that a ramp is provided for ingress of a passenger with the assistive device. The ramp can have a substantially smooth surface that gradually inclines to a landing section. The incline can be set such that passengers with limited mobility and dexterity can traverse the ramp to the loading section. According to the embodiments described herein, the landing section can be wide enough such that one passenger with an assistive device can remain stationary on the landing section away from the ramp, while a second passenger with a second assistive device can enter the landing section adjacent to the ramp. Moreover, the landing section can be wide enough such that the second passenger with the second assistive device is provided with a substantially flat surface that allows the second assistive device to be turned towards the passenger section without disturbing the passenger with the assistive device or contacting other interior components (e.g., hand rails, seats, elevated ridges, and the like). Accordingly, the landing section can be utilized as a location to collect fairs or for any other purpose that leads to grouping of passengers or assistive devices. 
     The passenger section can gradually incline, at a rate less than the entrance ramp, backwards towards a step to an elevated passenger section. The step can include a retractable step that articulates into a ramp or a step. Accordingly, during ingress or egress the ramp can be provided to allow access to the elevated passenger section for passengers with assistive devices. For example, the retractable ramp can be lowered contemporaneously with the kneeling of the vehicle. Thus, ingress or egress to all sections of the vehicle can be provided to handicapped passengers. 
     It is noted that the terms “substantially” and “about” may be utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. These terms are also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue. 
     While particular embodiments have been illustrated and described herein, it should be understood that various other changes and modifications may be made without departing from the spirit and scope of the claimed subject matter. Moreover, although various aspects of the claimed subject matter have been described herein, such aspects need not be utilized in combination. It is therefore intended that the appended claims cover all such changes and modifications that are within the scope of the claimed subject matter.