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TECHNICAL FIELD 
     This invention relates to the field of road safety and more particularly to safety markers. 
     BACKGROUND OF THE ART 
     Transportation using motor vehicles is an integral part of the daily life of a large part of humanity. The speed, efficiency and convenience of modern road systems have improved a great deal since the time when the first roads were built. The safety of motor vehicles has also increased substantially over recent years. 
     Despite these improvements, roughly 30 thousand people lose their life and 2 million people are injured in the more than 10 million vehicle accidents reported each year in the United States alone. 
     Highway vehicle accident scenes are very dangerous since they create a stationary obstacle while incoming vehicles travel at high-speed. First respondents to a vehicle crash site face the most dangerous task of setting up the initial security perimeter aiming at diverting the incoming traffic away from the damaged vehicles and injured passengers. Each year in the United States alone, millions of law officers and first respondents risk their life working on roads and thousands are injured or die every year because of the unavailability of adequate tools to perform these tasks safely. 
     “Move over” laws have been passed in the great majority of the US states and in all Canadian provinces. These laws make it compulsory for drivers to slow down or change lanes and move away from stopped emergency vehicles. Despite these laws, too many accidents still occur every year. 
     Various types of road safety markers exist but the prior art systems have many drawbacks and limitations. There is still a need for a road safety marker which can be disposed quickly and efficiently on the road by the first respondents, either manually or through an automated dispenser. 
     SUMMARY 
     A safety road marker is provided. It contributes to establish a safety perimeter and helps divert incoming traffic. 
     According to one broad aspect of the present invention, there is provided a safety marker apparatus comprising a hollow body including at least four vertex elements interconnected by flexible resilient rods, the body being adapted to be compressed into a stowed state upon application of an external force and expanded into a deployed state, the flexible resilient rods forcing the hollow body to adopt the deployed state in an absence of the external force. 
     In one embodiment, an illumination sub-system is provided in at least one vertex element. 
     In one embodiment, the safety marker further comprises at least one fabric sheet, the fabric sheet being attached to the hollow body, the fabric sheet being flexible and adapted to move with air circulation. 
     In one embodiment, the safety marker further comprises an encapsulating shell for receiving and retaining the body in the stowed state. 
     In one embodiment, one of the at least four vertex elements is adapted to mate with others of the at least four vertex elements in the stowed state. 
     In one embodiment, the safety marker further comprises a retaining band, the retaining band being adapted to retain the body in the stowed state. 
     In one embodiment, the safety marker further comprises at least one retro-reflecting element affixed to the body. 
     In one embodiment, a configuration of the vertex elements and the rods provides a substantially symmetrical hollow body. 
     In one embodiment, the at least four vertex elements is four vertex elements and wherein the four vertex elements are interconnected by six flexible resilient rods. 
     In one embodiment, at least one of the four vertex elements is an illuminating vertex element, wherein the safety marker further comprises a battery-powered light source provided in the illuminating vertex elements, the battery-powered light source being switched on in the deployed state and being switched off in the stowed state. 
     In one embodiment, the safety marker further comprises a magnetic switch for the battery-powered light source and a permanent magnet, wherein the battery-powered light source is switched off by a proximity of the permanent magnet to the illuminating vertex element in the stowed state and switched on by a distance of the permanent magnet from the illuminating vertex element in the deployed state. 
     In one embodiment, the permanent magnet is provided on one of another one of the four vertex elements and a casing for the marker. 
     In one embodiment, the safety marker further comprises a controller for the battery-powered light source, the controller controlling the battery-powered light source to emit light one of continuously and intermittently. 
     In one embodiment, the safety marker further comprises an optical detector for detecting an illumination signal, wherein the controller controls at least one of a frequency and a timing of intermittent illumination of the battery-powered light source using the illumination signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, showing by way of illustration an example embodiment thereof and in which 
         FIG. 1  is a top view of a scene of a vehicle crash with a security perimeter and incoming traffic; 
         FIG. 2  is a perspective view of an example hollow tetrahedral marker with flags attached to three rods of the marker; 
         FIG. 3  includes  FIG. 3A ,  FIG. 3B ,  FIG. 3C ,  FIG. 3D ,  FIG. 3E  which show alternative geometrical shapes that can be used to construct hollow markers; 
         FIG. 4  includes  FIG. 4A ,  FIG. 4B ,  FIG. 4C  in which  FIG. 4A  shows the marker of  FIG. 2 ,  FIG. 4B  is the marker of  FIG. 4A  partially compressed into a ball and being inserted inside two hemispheric shells and  FIG. 4C  is the marker of  FIG. 4A  inserted inside the two hemispheric shells to form a self-contained ball; 
         FIG. 5  is a perspective view of another example hollow tetrahedral marker using two different types of vertices; 
         FIG. 6  includes  FIG. 6A ,  FIG. 6B ,  FIG. 6C  and  FIG. 6D  in which  FIG. 6A  is the marker of  FIG. 5  in the stowed state,  FIG. 6B  is the marker of  FIG. 6A  in a state one-third deployed,  FIG. 6C  is the marker of  FIG. 6A  in a state two thirds deployed and  FIG. 6D  is the marker of  FIG. 6A  in the deployed state; 
         FIG. 7  is an exploded view of the principal vertex of the marker shown in  FIG. 5 ; 
         FIG. 8  is an example schematic of the electronic circuit contained in the principal vertex of the marker shown in  FIG. 5 ; 
         FIG. 9  is an internal view of the vertices of the marker shown in  FIG. 5  showing magnetic switches and magnets; 
         FIG. 10  is block diagram of an example marker dispenser and a peripheral connection to the vehicle to which it is attached; 
         FIG. 11  includes  FIG. 11A  and  FIG. 11B  in which  FIG. 11A  is an illustration of an example safety marker dispenser installed on a rear bumper of a car and  FIG. 11B  is an illustration of the example safety marker dispenser shown in  FIG. 11A  showing an internal marker cartridge; 
         FIG. 12  is an illustration of the deployment phases of the example hollow marker shown in  FIG. 5 ; 
         FIG. 13  is an illustration of the deployment phases of the example encapsulated hollow marker shown in  FIG. 2 . 
     
    
    
     It will be noted that throughout the appended drawings, like features are identified by like reference numerals. 
     DETAILED DESCRIPTION 
       FIG. 1  depicts a crash scene  101  on a highway  102 . The highway includes two lanes of left-bound traffic  104   a ,  104   b  and two lanes of right-bound traffic  106   a ,  106   b . Vehicle  105  has collided with another vehicle  107  at a crash site  103  in left-bound lane  104   a . A police vehicle  109  is present at the scene. Vehicles  111  and  113  are part of the incoming traffic in left-bound lanes  104   a ,  104   b . Vehicle  111  has trajectory  119  and vehicle  113  has trajectory  123 . 
     The crash site  103  will be made safer if the incoming traffic is diverted to the other left-bound lane  104   b . Safety perimeter  115  can be established by the first respondent, in this case the police officer. The safety perimeter  115  indicates to the drivers of the incoming vehicles that they should move their vehicle towards the centerline  117 , away from the crash site  103 . Incoming vehicle  111  should be enticed to follow a safe trajectory  119  towards the centerline  117 , in order to lower the chance of collision with the vehicles  105 ,  107  at the crash site  103  and the persons walking around the crash site  103 . One method of setting up a safety perimeter  115  consists of placing individual safety markers  121  at substantially regular intervals over a length of road preceding the crash site  103 . 
     In one embodiment of the invention shown in  FIG. 2 , the safety marker  201  consists of a hollow tetrahedral structure. In this example embodiment, the four vertices  203  of the tetrahedron are connected by rods  205  and  207 , made of a flexible and springy material. This material can be a metal spring coil, a springy plastic material or any other suitable materials. For example, the rod can be made of ASTM-A227 or ASTM-A764 compliant material of HDMB quality. It can have a Bezelplast colored coating or can be galvanized. The rod may be tubular, planar or other. 
     Although illustrated as spheres, the vertex elements need not be enclosed structures. The outside portion of vertices  203  which is meant to contact the ground can be made of a variety of materials, for example rubber or plastic. It can be roughened to improve adherence to the surface on which it rests. The inside portion of the vertices  203  which faces the interior of the hollow structure is protected from an impact with the ground by the body of the marker. It can be made of the same material as the outside portion or can be made of a different material. For example the vertex elements can be made of acrylic, polymers or epoxy. 
     The hollow body of the safety marker forms a structure which has a height sufficient to attract the attention of the drivers of the incoming vehicles. In an example embodiment, the height of the hollow body is 14 inches. The length of the rod, in an embodiment in which the hollow tetrahedral structure is regular is 9 inches. The size of the rod is sufficient to allow the tetrahedral structure to stand and withstand winds. An example diameter for the rod, if it is cylindrical, is 4 mm. 
     Hollow marker structures present a small surface area and are less susceptible to being pushed or blown from their intended position by wind and air currents. 
     Rods  205  are equipped with small flags  209  made of a fabric-like material such as a thin polymer sheet or coated nylon sheet. This material can be dyed or coated with a bright color such as orange. Optionally the material can also reflect light preferentially towards the source of illumination in order to increase its visibility during nighttime. Note that in another embodiment of the invention, all rods  205  and  207  can be equipped with such small flags  209 . 
     The connecting rods  205  and  207  can also feature a reflective coating in order to enhance their visibility. Optionally, retro-reflective elements can be affixed to the rods or the vertex elements. The rods themselves could also be illuminated. 
     Optionally, the vertices are embedded with battery-powered light sources, in order for the marker to be as visible as possible during nighttime. The light sources can be Light Emitting Diodes (LED), incandescent bulbs or any other suitable source of light. The lights can be operated to emit light continuously or in a flashing manner, thus being more noticeable while saving battery power. The emitted light can be white, red or of another suitable color. A light source bundle can be used wherein more than one color is emitted. The light sources are contained in vertex enclosures, here depicted as small spheres. The vertex enclosures are preferably translucent. The outer surface of the enclosure can be roughened in order to diffuse outgoing light and appear as a large emitter source. In another embodiment, light sources could also be embedded in at least some of the connecting rods  205  and  207 . 
     Optionally, a central illuminating element could be provided. This central illuminating element would be attached to at least one vertex element and be provided within the hollow body of the marker, for example by gravity. This central illuminating element would be provided with a battery-powered light source similar to that optionally used in the vertex elements. 
     It is understood that geometric shapes other than the tetrahedron shown in  FIG. 2  can be used to create a marker with desirable properties.  FIG. 3  shows several examples of alternate geometric shapes for the marker, including a rectangular parallelepiped  303  ( FIG. 3A ), a cube  305  ( FIG. 3B ), a triangular prism  307  ( FIG. 3C ), square pyramid  309  ( FIG. 3D ) and a pyramidal fustrum  311  ( FIG. 3E ). 
     Hollow geometric structures composed of vertices and flexible rods can be compressed into a very small volume for stowage.  FIG. 4A ,  FIG. 4B  and  FIG. 4C  show an encapsulation sequence of a hollow tetrahedral marker  401  into a ball  405 . The ball  405  is composed of two hemispherical hollow shells  407 . Starting from its deployed state shown in  FIG. 4A , the tetrahedral marker  401  is collapsed onto itself until the vertices  203  touch or almost touch as in  FIG. 4B . In  FIG. 4B  the compressed marker  401  is seen with the rods  403  wrapped around the vertices  203  and being inserted in the hollow shells  407 . In  FIG. 4C  the marker  401  is completely encapsulated in a stowed marker ball  405 . The two hollow shells are affixed to one another using means known in the art. As will be readily understood the hollow shells could be of different shapes to create an encapsulated marker with a shape other than a sphere, such as a conical structure or a disk, for example. 
       FIG. 5  shows another example embodiment of a marker  501 . In this example embodiment, six flexible rods  507  connect the primary vertex  503  and the three secondary vertices  505  of the tetrahedron. 
     The vertices  503 ,  505  of the example embodiment safety marker shown in  FIG. 5  are designed to mate in the manner illustrated in  FIG. 6A .  FIG. 6A  shows the safety marker  601  packaged in its stowed state. In this configuration, the three secondary vertices  505  form a hollow cylinder around the stem  609  of the primary vertex  503 , constructing a compact vertex subassembly  611 . The flexible rods  507  are neatly folded in two under the vertex assembly  611 . A retainer band made of flexible material can be wrapped around the flexible rods  507 , or around the three secondary vertices  505  in order to maintain the safety marker  601  in its stowed state. The retainer band can be a Velcro™ strip affixed to one of the rods. 
       FIG. 6B  shows the safety marker  601  being released from its stowed state. The spring restoring force of the flexible rods  507  can contribute in pulling the three secondary vertices  505  apart from the primary vertex  503 .  FIG. 6C  shows the safety marker  601  at a further intermediary stage of deployment. 
       FIG. 6D  shows the fully deployed marker  601 . Note that in this deployed state, the marker  601  can also be oriented with the primary vertex  503  in one of the lower positions and with one of the secondary vertices  505  in the upper position. 
       FIG. 7  shows an exploded view of an example embodiment of the primary vertex  701  of the marker  501 . The lower part  703  of the primary vertex enclosure can be made of a plastic shell with a hollow cylindrical part  702  terminated with a circular end  704  at the bottom where a round hole is placed to allow a light emitting diode  705  to be positioned and to protrude in the cylindrical part  702  of the lower part  703 . This light emitting diode  705  can thus shine light on the marker  501  in its deployed state including on the flags installed on the marker rods  207 . Alternatively, the light emitting diode  705  can be enclosed in the lower part  703  of the primary vertex, if this section of the enclosure is made of a transparent material. 
     An assembly of batteries  707  used to power the light emitting diode  705  as well as additional light emitting diodes  709  is shown in  FIG. 7 . These batteries  707  fit inside the hollow cylindrical part  702  in the lower part  703 . Five such batteries  707  are used. The three light emitting diodes  709  can be positioned using a transparent cylinder  711  featuring three holes  713 . 
     The upper section of the enclosure also includes a magnetic switch  715  and three magnets  717 . The magnetic switch  715  is used to switch the primary vertex light emitting diodes electrical circuit on and off, as described in  FIG. 8 . The magnets  717  are used to switch the secondary vertex light emitting diodes electrical circuit on and off, as illustrated in  FIG. 9 . 
     The example primary vertex assembly can be protected from the elements (rain, snow, dust, etc.) by affixing and/or sealing the lower part  703  and upper shell  719  together. The upper shell  719  can be made of a translucent material to allow the three upper light emitting diodes  709  to emit light towards external observers. The electric components of this example primary vertex assembly can be connected using printed circuit boards and wires (not shown in  FIG. 7 ). 
     As will be readily understood, a handle can be provided on the exterior surface of the upper shell  719  to facilitate transportation of the marker by a user. 
       FIG. 8  shows an example electrical circuit  801  used to power the light emitting diodes  705  and  709 . In this example the light emitting diodes are connected in series and are powered using battery set  809 . The light emitting diodes  705  and  709  are turned on and off using a magnetic switch  715  placed in series with the light emitting diodes  705  and  709  and battery set  809 . When there is no magnetic stimulation, the magnetic switch  715  is closed and the light emitting diodes emit light. When a magnetic field is present in the vicinity of the magnetic switch  715 , the magnetic switch opens the electrical circuit  801  and the light emitting diodes cannot emit light. Bringing a permanent magnet  805  close to the magnetic switch  715  can generate a magnetic field and interrupt the circuit. 
     The electrical circuit  801  can also be equipped with an intermittent switch  807 , causing the light emitting diodes to emit flashes of light instead of a continuous luminous flux. This mode of operation is more noticeable to an observer while consuming less power. This intermittent switch can in some cases be integrated in one of the light emitting diodes, such as light emitting diode  705 . 
     The secondary vertices can be equipped with similar circuits as described in  FIG. 8  to allow the secondary vertices to also emit light, thereby improving the visibility of the safety marker. 
     In another embodiment, the magnetic switch is replaced by a mechanical switch. During stowage, a portion of the marker abuts a pressure switch for the battery-powered light source. Once the marker is deployed, the pressure switch is freed and the light source is turned on. Another type of mechanical switch is a shock switch. The light source could be turned on upon contact by the marker with the ground above a certain speed. 
     In another embodiment, a plastic or cardboard sheet is inserted between two batteries of the battery set for the battery-powered light source prior to stowage. An end of this sheet protrudes from the vertex elements. During stowage, the plastic or cardboard sheet prevents the two batteries from contacting one another and therefore ensures that the light source remains off. Upon deployment, the sheet is removed, either manually or by an automated pull of the sheet. The two batteries then enter in contact since they are spring-loaded in the battery compartment. The light source turns on. 
       FIG. 9  shows an example relative positioning of the primary vertex magnetic switch  715  and primary vertex magnets  903 ,  905  and  907 , as well as the secondary vertex magnetic switches  909 ,  911  and  913  and the secondary vertex magnet  915 . In this example the secondary vertices  917 ,  919  and  921  are separated from the primary vertex  923 , thereby deactivating the magnetic switches and allowing the light emitting diode circuits to operate. 
     The primary vertex magnetic switch  715  is activated by the magnet  915  installed in the secondary vertex  917 , when the safety marker is in the stowed position as illustrated in  FIG. 6A . Similarly each secondary vertex has a magnetic switch that can be activated by a permanent magnet installed in the primary vertex  923 . When the safety marker is in the stowed position, the primary vertex magnet  903  activates the magnetic switch  909  of secondary vertex  917 , preventing the secondary vertex  917  light emitting diode circuit to operate. Likewise in this stowed position, the primary vertex magnet  905  activates the magnetic switch  913  of secondary vertex  921  and the primary vertex magnet  907  activates the magnetic switch  911  of secondary vertex  919 . In this configuration, none of the secondary vertex  917  light emitting diode circuits can operate. 
     In another embodiment, the magnetic switch is composed of a permanent magnet on a casing and of a magnetic field activated switch for each battery-powered light source in the marker. During stowage, the casing is placed in proximity to the magnetic field activated switch and ensures that the battery-powered light source remains off. When the casing is removed, the permanent magnet is moved away from the magnetic switch, thereby allowing the battery-powered light source to be turned on. The casing can also serve as the element which applies an external force on the marker to keep it in the stowed configuration. Upon removal of the casing, the marker is freed and achieves its deployed configuration. 
     Alternatively, the light emitting diodes in a safety marker could be powered using a single electrical circuit instead of having one independent circuit per vertex. With a single electrical circuit per safety marker, wires have to be installed inside or along the marker rods. 
     As will be readily understood, the markers can be deployed manually from their stowed state to their deployed state. The user simply removes the element which creates the external force applied onto the marker in the stowed state and the hollow body adopts the deployed state in an absence of the external force. The element which creates the external force can be a retaining band, a casing, a magnet, a shell, a polymer wrapping, etc. Once deployed, the markers can be manually positioned on the surface as required. 
     Alternatively, the markers can be deployed and positioned using an automatic dispensing system.  FIG. 10  shows a block diagram  1001  for an example embodiment of a safety marker dispenser system  1003 . Multiple markers are stored inside a marker storage device  1005  (e.g. a magazine or a cartridge) in order to allow the deployment of an appropriate number of safety markers to construct an adequately sized safety perimeter  115 . The marker dispenser system  1003  can feature a marker handling subsystem  1007  to bring one marker at a time towards a marker ejector  1009 . The dispenser controller  1011  orchestrates the action of the marker handler  1007  and the marker ejector  1009  in order to correctly dispense the markers. 
     The ejection mechanism contained in the marker ejector  1009  can be modulated in order to achieve a variable amount of force exerted on the ejected marker and consequently a variable exiting speed of the ejected marker. In one embodiment of the invention, the markers are ejected with the opposite velocity of the vehicle  1019  carrying the dispenser  1003 . In this case, the markers appear to be dropped vertically from the dispenser with little horizontal velocity with respect to the road. This condition ensures that the markers fall close to the ejection point and minimizes the risk of having markers bounce off the road surface and follow unpredictable trajectories. 
     It is understood that several methods can be utilized to eject the markers from the marker dispenser including: rotating wheels, mechanically compressed or elongated springs, mechanical cams, hydraulic and pneumatic approaches or combinations of these methods. 
     In order for this relative velocity nulling function to be implemented, the information on the speed of the vehicle  1019  needs to be taken into account by the dispenser controller  1011 . One approach is to include a global positioning system (GPS)  1013  in the dispenser system  1003  and have the dispenser controller  1011  calculate the speed by taking the derivative of the position with respect to time. An alternative approach is to transmit to the dispenser controller  1011  the speed information if available in the vehicle  1019  to which the marker dispenser  1003  is attached. In this case, the speed information can be transmitted using either an electrical analog signal, an electrical digital signal or a mechanical method. Other approaches can also be used to derive the vehicle speed, including air pressure sensing or optical monitoring of the road surface. Regardless of the method used to derive the velocity information, it can be used to modulate the amplitude of the ejection mechanism in order to impart to the marker a velocity that compensates the velocity of the vehicle to which the marker dispenser is attached. 
     In one embodiment of the invention, the speed information is also used to control the deployment of markers. Indeed, a lower speed limit, for example 30 km/h (or any other desired value), can be programmed in the dispenser controller  1011  as a condition to meet in order to permit the deployment. If the vehicle is travelling at a speed lower than this lower limit, including being stationary, the dispenser controller  1011  will not allow the deployment of markers. Similarly, an upper speed limit, for example 100 km/h (or any other desired value), can also be programmed to restrict deployment when the first respondent&#39;s vehicle is travelling at normal highway speeds. In this case, the deployment is allowed when the respondent&#39;s vehicle slows down at a speed lower than the upper limit, as it approaches the scene. 
     In one embodiment of the invention the deployment of the markers is triggered without user action when the vehicle carrying the marker dispenser comes in the geographical vicinity of the site of the accident. This approach requires an accurate knowledge of the position of the respondent&#39;s vehicle either by using a vehicle GPS  1015  or a GPS  1013  embedded in the marker dispenser system. This approach also requires the knowledge of precise spatial coordinates of the site of the accident. This information can be obtained by standard communications networks, such as cellular, digital data or short-wave radio. 
     In another embodiment of the invention, it is the occupants of the vehicle that decide when to deploy the markers. While approaching the scene of the accident, the occupants decide when to deploy the safety perimeter by pressing a deployment button or trigger  1017  located inside the vehicle. This button can communicate with the dispenser controller  1011  inside the marker dispenser  1003  via a wireless radio-frequency link or alternatively via a wire running from the deploy button or trigger  1017  to the marker dispenser  1003 . The wireless radio-frequency link can be installed easily and enables a rich communication path allowing to relay status information from the marker dispenser  1003  to the occupants of the vehicle regarding the deployment operation. This status information can include for example the system states including standby, on-going deployment, deployment completed or malfunction, as well as the number of marker deployed. This information could appear near the deploy button, on a small liquid crystal display, light emitting diode display, or could be represented using a set of discrete light emitting diode indicators. 
     The marker dispenser  1003  can be connected to the vehicle power or alternatively, it can operate on internal battery power. 
       FIG. 11A  shows an example embodiment of the invention where the marker dispenser  1103  is installed on the rear bumper  1107  near the trunk  1105  of a respondent&#39;s vehicle  1101 . The marker dispenser  1103  can be secured using a number of methods including bolting on the bumper  1107  or mounting on the vehicle hitch interface. 
       FIG. 11B  shows the same example marker dispenser  1103  with its door  1111  open. The stowed markers can be stored inside a removable marker cartridge  1113  that can be replaced quickly after usage. 
     During the deployment process the markers go through a number of phases.  FIG. 12  shows three main phases of the deployment of the marker presented in  FIG. 6A to 6D , namely the ejection phase  1203 , the expansion phase  1205  and the landing phase  1207 . During the ejection phase  1203 , the marker is ejected from the marker dispenser  1209 . In the expansion phase  1205 , the springy marker rods straighten and return to their nearly linear form allowing the marker to attain its expanded state. In the landing phase, the marker touches the ground at the target location. 
       FIG. 13  shows the four main phases of the alternate marker presented in  FIGS. 4A to 4C , namely the ejection phase  1303 , the liberation phase  1305 , the expansion phase  1307  and the landing phase  1309 . During the ejection phase  1303 , the marker located in its encapsulation shells is ejected from the marker dispenser  1311 . During the liberation phase  1305 , the marker encapsulation shells are allowed to separate in order to release the marker. The other phases are identical to those presented in the previous paragraph. 
     In one embodiment of the invention, the encapsulation shells are separated under the strength of the impact of the ball with the ground. In one embodiment, after release of the marker, the encapsulation shells remain attached to the vertices or the rods. In another embodiment, the encapsulation shells are part of the vertex elements, each vertex element having a section of the encapsulation shell adapted to mate with the others to form the ball. 
     In one embodiment of the invention, the method used to maintain the encapsulated marker presented in  FIG. 4A to 4C  is an elastic membrane similar to the latex used in common inflatable birthday balloons. As the markers are ejected, their surface come in contact with sharp blades located inside the ejection mechanism, thereby causing small cuts in the elastic membrane which rips apart due to its high surface tension, thus separating the enclosing shells and freeing the marker. In another embodiment, no shells are used and the marker is enclosed directly inside the flexible membrane. 
     In one embodiment of the invention, the markers are designed so that the light flashes emitted by markers is synchronized to improve visibility, to improve depth perception and to minimize visual confusion. In one mode the markers can flash simultaneously. In another mode the markers emit a “chase” waveform, that is a flash of light from one marker at a time, in the order from the farther to the closer to the dispenser. This mode provides a better depth perception and suggests a safe obstacle-avoiding path to the drivers of incoming traffic. Other synchronized modes of lighting such as a “chase” waveform from the closer to the farther to the dispenser, or combinations can also be implemented. 
     The synchronization of the marker flashing can be performed using a synchronization radio frequency signal emitted by a circuit located in the marker dispenser. This master signal can instruct each marker when to emit their flash. Alternatively, the master signal can emit a signal to synchronize clocks embedded in each marker. This synchronization of clock process can be quite infrequent, depending on the accuracy of the marker clocks. The markers can follow the sequence with a common fixed period and with a delay that is preprogrammed in each of them. The spatial ordering (chase effect) of the flashes is achieved by the correct ordering of the markers inside the marker cartridge at factory. 
     Alternatively, the marker light emission can be regulated by marker-to-marker communication. This communication can be achieved using radio frequency, optical communication or any other suitable method. 
     Radio frequency synchronization between markers may require unique marker identification numbers and ordering in the cartridge, for the flashes to be spatially ordered (chase effect) when deployed. 
     Optical communication for inter-marker synchronization requires the use of a photodetector in each marker to sense the ambient light. The light emission capability is already present; it is the light sources used to produce the flashes. The photodetector can also be used to sense ambient light and to suppress flashing during daytime. This feature is useful to save battery power. 
     Using the optical approach at nighttime, the markers can synchronize with the other markers simply by establishing a master—slaves configuration. As soon as one marker is deployed and triggered, this marker monitors and “looks” for a few (for example three) light flashes at a nominal frequency f. If no such flashes are detected, it is because this is the first marker, so it becomes the master and starts flashing at the nominal frequency f, for example one flash per second. For the other markers, as soon as a few (for example three) flashes are detected, the receiving marker becomes a slave and from this point on, the slave marker will echo detected flashes that match (within a tolerance margin) the amplitude of the initial flashes. A small delay of a fraction of a second is used between the detection and the emission in order to create the chase effect. After a slave marker has echoed a flash, it inhibits echoing of other detected flashes for a time period slightly shorter than the cycle time to avoid picking up flashes from other slaves down the line and create double echoes. 
     After usage, the markers can be picked up manually and stored in a bag for return to the factory, where they can be refurbished into a new cartridge. 
     The applications for this invention are numerous. The applications include the set-up of a safety perimeter to protect first respondents at a site of a road accident including: paramedics, law officers, firemen, and tow truck operators. Other applications include the protection of workers at a site of a road spill, of utilities employees working near roads, of road construction workers, of children playing basketball or hockey in the street, of emergency personnel caring to an injured skier on a ski slope, etc. The markers are therefore useful to divert traffic by creating a visual indicator, irrespective of the type of traffic (humans, vehicles, etc). 
     The embodiments described above are intended to be exemplary only.

Summary:
A safety marker apparatus comprising a hollow body including at least four vertex elements interconnected by flexible resilient rods, the body being adapted to be compressed into a stowed state upon application of an external force and expanded into a deployed state, the flexible resilient rods forcing the hollow body to adopt the deployed state in an absence of the external force. In one embodiment, an illumination sub-system is provided in at least one vertex element.