fig1 is a plan view from above a car 2 mounted within a hoistway 10 of an elevator system 1 . two guide shoes 6 mounted on opposing sides of the car 2 slide along corresponding guide rails 12 affixed to opposing walls of the hoistway 10 to retain the car 2 in a centralized position as it moves up and down ( out of and into the plane of the page ) within the hoistway 10 . a stop bar 20 according to the present invention is stored on a rooftop 4 of the car 2 . fig2 is an expanded view of segment a of fig1 showing in more detail the relationship between one of the guide shoes 6 and the associated guide rail 12 . the guide rail 12 comprises a support flange 14 and a guide blade 16 extending in towards the center of the hoistway 10 . the guide rail 12 is positioned and mounted onto the hoistway 10 by fixing bolts 18 that pass through the support flange 14 and is secured thereto by corresponding nuts 19 , the bolts 18 and nuts 19 serve as engagement members , as will become clear from the discussion below . the guide shoe 6 is provided with a slot 8 that partially envelops the guide blade 16 . accordingly , the car 2 is prevented from moving significantly away from its central line of travel by engagement of the guide blade 16 with the side walls of the slot 8 . when maintenance / inspection work is to be carried out in the hoistway 10 the technician stops the car 2 at a predetermined level in the vicinity of a specific landing door of the hoistway 10 , opens that landing door and climbs onto the roof 4 of the car 2 . from there the technician switches the control system of the elevator 1 to inspection mode thereby enabling the car 2 to travel at a reduced speed upwards or downwards within the hoistway 10 under the supervision of the technician . in order to create a temporary safety space above the car 2 , the stop bar 20 is arranged as shown in fig3 and 4 . the stop bar 20 has opposing ends each having two support struts 26 with a channel 24 therebetween . initially the technician moves the car 2 up towards , but not into , the proposed temporary safety space . then the stop bar 20 is removed from its stored position , as shown in fig1 , and the guide blades 16 of the guide rails 12 are inserted into the opposing channels 24 of the stop bar 20 . the car 2 is then moved upwards slightly until the support struts 26 bear against a lower surface of the nuts 19 securing the guide rail 12 to the hoistway 10 , as shown specifically in fig4 . in this position , with the stop bar 20 sandwiched between the roof 4 of the car 2 and the nuts 19 , the car 2 is prevented from further upward motion and thereby the upper safety space is created . to reduce the initial and any subsequent impact forces between the stop bar 20 and the car 2 a layer of resilient material 22 such as rubber is provided on the lower surface of the stop bar 20 . in order to create a temporary safety space in a pit of the hoistway 10 below the car 2 , the stop bar 20 is arranged as shown in fig5 . initially the technician moves the car 2 down towards , but not into , the proposed temporary safety space . then the stop bar 20 is removed from its stored position , as shown in fig1 , and again the guide blades 16 of the guide rails 12 are inserted into the opposing channels 24 in the stop bar 20 . on this occasion , however , the stop bar 20 must be fixed to the roof 4 of the car 2 . this is achieved by inserting bolts 30 through slots 28 provided in the bar 20 and fastening them to the roof 4 of the car 2 . the car 2 can then be moved downwards slightly until the support struts 26 bear against an upper surface of the nuts 19 securing the guide rail 12 to the hoistway 10 . in this position , the car 2 is prevented from further downward motion and thereby the lower safety space is created . although the guide shoes 6 of this particular embodiment are positioned at the top of the car 2 , it will be appreciated that the shoes 6 can be mounted at any position along the height of the car 2 . over time the opposing guide rails 12 of an elevator system 1 can become misaligned . accordingly , the distance between them can vary along the length of the hoistway 10 . the stop bar 20 of the previously described embodiment , being of a single - piece construction , cannot account or adjust for these changes . accordingly , an alternative , telescopic stop bar 40 as shown in fig6 was developed . the stop bar 40 shares all of the features of the previous embodiment but additionally it is of a two - piece construction . the ends of the stop bar 40 are biased against each other by a compression spring 32 . hence the stop bar 40 automatically adjusts to the distance between the opposing guide rails 12 even if that distance changes along the length of the hoistway 10 . fig7 illustrates a manually adjustable stop bar 50 according to a third embodiment of the invention . again the stop bar 50 is of a two - piece , telescopic construction . when in position so that the stop bar 50 spans the distance between the opposing guide rails 12 , the technician locks the two pieces together by means of screw pin 34 . obviously the embodiments of fig6 and 7 can be combined so that the two telescopic pieces of the stop bar are locked together in the stored position so that it is of minimal length . then , when required , the screw pin 34 can be released and the compression spring 32 forces the two pieces apart to engage with the opposing guide rails 12 within the hoistway 10 . instead of using the bolts 18 and the nuts 19 on the guide rails 12 , temporary fastening means such a clamp or bolt could be used to secure the ends of the stop against the guide rails 12 as illustrated in fig8 which shows a further stop bar 60 in accordance with a fourth embodiment of the invention . the arrangement shown is similar to that of fig4 but it will be appreciated that the stop bar 60 is shorter than that of fig4 . again when maintenance inspection work is to be carried out in the hoistway 10 the technician stops the car 2 at a predetermined level in the vicinity of a specific landing door of the hoistway 10 , opens that landing door and climbs onto the roof 4 of the car 2 . instead of manually switching the control system of the elevator 1 to inspection mode , the technician merely removes the stop bar 60 from its stored position ( fig1 ) and mounts it across the car roof 4 between the opposing guide rails 12 as shown in fig8 . in this position an electrical contact 66 on each side of the underside of the stop bar 60 contacts an associated electrode 68 extending from the car roof 4 to complete a bridge circuit thereby automatically switching the control circuit of the elevator 1 to inspection mode . as the support struts 62 of this embodiment are shorter than in the previous embodiments , the technician is capable of moving the car 2 up towards the proposed temporary safety space without fouling against the nuts 19 and the bolts 18 securing the guide rails 12 to the hoistway 10 . in that position , the technician screws temporary bolts 64 into threaded holes 15 on the opposing guide rails 12 and then continues to move the car 2 upwards until the support struts 62 bear against the temporary bolts 64 . the car 2 is prevented from further upward motion and thereby the upper safety space is created . a further arrangement is also envisaged wherein the support struts are longer than in the embodiment shown in fig4 and instead of engaging with nuts or bolts mounted on or through the opposing guide rails , the struts capable of extending into holes provided at regular distances along the support flanges of the opposing guide rails . naturally such a stop bar would have to be telescopic since its extended length is inherently greater than the distance between the opposing guide rails . since the maintenance technician must generally climb onto the roof 4 of the car 2 to switch ( whether manually or through installation of the stop bar 60 ) the control system of the elevator 1 to inspection mode , the roof 4 is the most logical place to store and install the stop bar 20 , 40 , 50 , or 60 . however , it will be appreciated that the stop bar 20 , 40 , 50 or 60 could alternatively be installed on the bottom of the car or indeed on a counterweight of the elevator 1 having its own guide rails . although the present invention has been described in relation to particular embodiments thereof , many other variations and modifications and other uses will become apparent to those skilled in the art . it is preferred , therefore , that the present invention be limited not by the specific disclosure herein , but only by the appended claims .