in the following detailed description , certain specific terminology will be employed for the sake of clarity and a particular embodiment described in accordance with the requirements of 35 usc 112 , but it is to be understood that the same is not intended to be limiting and should not be so construed inasmuch as the invention is capable of taking many forms and variations within the scope of the appended claims . referring to fig1 an entrance section 10 for an auto wash conveyor is shown , which includes a three tier frame structure 12 . a chain take up mechanism 14 and roller control mechanism 16 are mounted as a unit 15 at the entrance end of the entrance conveyor section 10 as will be described below in additional detail . an upper track 18 is defined by two separate angles 20 separated to form a slot 22 through which an elevated roller assembly 80 extends . a car &# 39 ; s tires roll along the flat surface defined by the top of each angle 20 , pushed along by an elevated roller assembly having one roller set moving along on the top of the angles 20 so as to engage the car &# 39 ; s tire to push the same down the track by the pull of the roller chain . u . s . pat . no . 4 , 864 , 936 describes one type of suitable roller assembly , while pending u . s . application ser . no . 09 / 260 , 321 , filed on mar . 1 , 1999 describes another roller assembly design . other roller assembly designs are commercially available and well known . a lower track 24 provides a return track for the roller assemblies 80 , and an intermediate track 26 receives roller assemblies 80 which are being pulled in a forward direction but have not been activated by causing one end to be diverted up to the top track by selective operation of the roller control mechanism 16 in the well known manner . the nature of the track structure is best understood by reference to fig2 - 4 . an intermediate conveyor section 28 ( fig2 ) is used between the entrance conveyor section 10 and an exit conveyor section 30 ( fig3 ) each having the upper track 18 , lower track section 24 , and intermediate track 26 . a series of flat steel support plates 32 are cut out by such processes as plasma cutting , water jet cutting , etc . into the modified “ h ” contour shown , comprised of a pair of legs 34 connected at the bottom by a lower web 36 and an intermediate web 38 . the upper track 18 includes the pair of steel angles 20 , each having one side lying horizontally and spaced apart to define the slot 26 . the angles 20 extend between two support plates 32 located at a respective end of a track segment of the entrance conveyor section 10 , the entire length of the intermediate conveyor section 28 , and a mid point location of the exit conveyor section 30 . modified flat plate supports 32 a and 32 b are used in the entrance section 10 on either end of the chain take - up mechanism 14 and roller control mechanism 16 . each support plate has a series of holes 42 for bolting adjacent conveyor sections together , and in the case of supports 32 a , 32 b to mount the unit 15 . the entrance section 10 has a transition segment 44 supported by a flat plate support 32 a and 32 c , which transition segment has a downwardly sloping lower track 24 a to properly position the roller assemblies ( not shown ) to be able to pass around the chain take up mechanism 14 . the intermediate conveyor section 28 has an additional plate support 32 at a point intermediate the ends of the section 28 ( which does not require the holes 42 ). the exit conveyor section 30 ( fig3 ) has a straight segment 46 and a transition segment 48 to a chain drive mounting structure 50 , comprised of a welded angle / plate construction for housing a conventional chain sprocket drive and exit trap door ( neither shown ). the flat plate supports 32 are welded to lengthwise extending downturned angles 20 defining upper track 18 , upturned angles 52 supporting uhmw plastic angles 54 forming the intermediate track 26 ( fig4 ), and upturned angles 56 forming lower track 24 . the downturned sides 58 of angles 20 and upturned sides 60 of the angles 52 are spaced to form a longitudinal slot 52 which is able to receive screw and nut attachments 65 for the uhmw angles 54 without the need for locating and drilling holes in the steel structure . the plate supports 32 and 32 b each have upwardly projecting portions 64 ( fig4 ) serving as stanchions for steel rods 66 on which are received a series of uhmw plastic rollers 68 serving as tire guides extending alongside the conveyor sections . a series of extra intermediate stanchions 74 are welded to the downturned leg 58 of the upper track angles 20 to provide additional support . an upright angle 70 is welded atop the other side of the supports 32 , to which a steel bar 72 is welded , serving as an inside tire guide . the use of the plate supports 32 , 32 a , 32 b , 32 c for the tracks 18 , 24 , 26 has a particular advantage in that the width of the upper cut out 76 can be made greater than the width b of the lower cut out 78 ( fig4 ), since straight angle members are not used and any contour can be cut in fabricating the supports 32 , 32 a , 32 b , 32 c . thus , the inside spacing c between the angles 52 may be set to be slightly wider than the width b of the lower cut out 78 to set the track width a the same , and to closely confine the chain 82 and roller assemblies 80 ( fig5 , 8 ) along both the intermediate track 26 and lower track 24 , which in turn reduces chain wear . also , as seen in fig5 a toe plate 84 is welded to the inside of the projections 64 stanchions 74 to block a person &# 39 ; s toes from entering the space above the track 18 , needed for safety considerations . fig7 shows the separate unit 15 removed from the conveyor track structure as a self contained unit . four parallel stainless steel rods 86 are arranged in a rectangular pattern symmetrical with respect to the axis of the chain 82 , attached at either end to h - shaped end plates 88 by couplings 90 having cross bolts ( not shown ) to secure the shaft ends therein . the chain take up mechanism 14 includes a take up driver 94 rotatably mounted by a shaft 96 supported on bearings 98 located on the outer side of a respective one of a pair of mounting plates 100 . the mounting plates 100 are each slidable on the shafts 86 by means of pairs of slider journals 102 on each shaft 86 ( using uhmw bearing sleeve 104 ). a tension spring 106 is compressed between spring seat 108 , fixed to a plate 110 extending between the side plates 100 to move therewith , and spring seat 112 fixed to end plate 88 . the roller control mechanism 16 selectively raises the unattached end of a roller assembly 80 to the upper track 18 to engage the tire of a car to be driven in the well known manner . the roller control mechanism 16 includes a pair of fork members 114 mounted on a cross shaft 116 pivotally supported with bearings 117 on side plates 118 . side plates 118 are each adjustable on the rods 86 by pairs of collars 120 secured in an adjusted position by set screws installed in the collars 120 . a direct drive actuator 122 , as described in u . s . pat . no . 4 , 864 , 936 , is directly connected to shaft 116 with a coupling 122 so that power pivoting of the shaft can be executed to move the fork members 114 to the up position shown , which causes the set of free end rollers to be routed up through the trap door 124 ( fig1 ) onto the upper track section 18 . the fork members 114 have lightening openings 126 to reduce their mass . cushioning stops 128 and 130 are located to quiet the impact of the fork members 114 in moving to the up and down positions . a handle ( not shown ) can be placed over exposed lever 132 for manual operation . the entire unit 15 can be installed or removed from the conveyor for easier maintenance . fig8 and 9 show that the entrance section 10 is specially configured to allow removal of the unit 15 without disturbing the track structure . the intermediate track 26 , and lower track 24 both terminate at the entrance end to create a cavity 134 bounded by support plates 32 a , 32 b . the upper track 18 extends over the cavity 134 and is supported by plate 32 b . an opening 136 is provided overlain by the trap door 124 ( fig1 ). the chain 82 solely supports the roller assemblies 80 in this region . a short segment 26 a is supported of support plates 32 a , 32 c , is configured to slope downwardly and with the angles 52 , 54 diverging from each other as shown in fig9 . this geometry insures recapture of the roller assemblies 80 as they move onto the intermediate track 26 a after being supported solely by the chain 82 in passing over the unit 15 . thus , the slight sag of the chain 82 in that region can be accommodated . the absence of the intermediate track section 26 and lower track 24 in that region allows a completely separate packaging of the chain take up and roller control in the unit 15 , to enable its removal together as a separate assembly . accordingly , a lower cost fabrication cost can be achieved with the above described features by a reduction in labor . at the same time , improved performance in several respects also results as described .