VMS installation is not a subject to be approached lightly

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VMS installation is not a subject to be approached lightly Powered By Docstoc
 by Roger Stainforth, VMS Limited, UK

Sign langu
VMS installation is not a subject to be approached lightly. Careful selection is
required to get the right coverage without wasting resources
          hen planning a journey a driver is      the traveller will be able to log on to the inter-   Radio stations, RDS-TMC and mobile tele-
 W        able to access information from
          many sources. Pre-trip information
                                                  net before setting out. The evidence, howev-
                                                  er, suggests that only a small proportion of
                                                                                                       phone services also provide sources of infor-
                                                                                                       mation. The paradox for the road operator is
can be obtained from maps, telephone serv-        travellers are motivated enough to rush to           that this vast amount of information is avail-
ices, the internet and motoring organisations     their computer (if they have one) and that           able to only a small percentage of drivers in-
to say nothing of informal enquiries to friends   journey planning most often begins when the          dividually. They may not have the equipment
who have recently travelled the route. There      key is inserted in the ignition.                     switched on or choose to ignore it if they
are also numerous journey planning systems                                                             think it does not apply to them. The delivery
already developed or still being developed,       In-trIp InformatIon                                  of the information will vary from one pro-
with the aim of influencing the travellers’       There is a steady uptake of satellite mapping        vider to another and lacks consistency.
choice of mode of travel. The assumption is       systems fitted as in-vehicle equipment to pro-          An effective driver information system
usually made by transport professionals that      vide instructions and information to drivers.        employing variable message signs (VMS) is


 110                                                                                                     TRAFFIC TECHNOLOGY INTERNATIONAL 2005

age                                                    It can be argued that when the message is
                                                    of a mandatory nature, for example, where
                                                    variable speed limit signs inform drivers of
                                                    speed limits that change in response to traffic
                                                    density, there is no alternative to the installa-
                                                    tion of Variable Speed Limit Signs (VSLS)
                                                    above each carriageway to avoid any doubt in
                                                    drivers’ minds. In this situation the in vehicle
                                                    equipment is at best supplementary.
                                                                                                          benefit of the driver (or customer as they are
                                                                                                          now sometimes referred to). From the driver’s
                                                                                                          point of view the only connection with the
                                                                                                          operator is probably the VMS. The driver has
                                                                                                          no knowledge of the unseen system and
                                                                                                          judges the credibility of the system by the in-
                                                                                                          formation displayed. Therefore, the return on
                                                                                                          the ITS investment can be lost if the messages
                                                                                                          are irrelevant and unreadable.
                                                                                                              In 1988 the Federal Department of Trans-
                                                    ItS credIbILIty                                       port in Washington, D.C., in response to the
                                                    If the above establishes the operational rea-         poor performance of early driver information
                                                    sons for deploying VMS, then the financial            systems, commissioned research to identify
the road operator’s critical interface with driv-   case can be just as compelling. The invest-           the criteria for the successful implementation
ers in three vital ways. First, VMS displays        ment in an intelligent transport system in-           of these systems. The recommendations
information to all drivers regardless of the        volves a large expenditure in time and money.         included four main criteria for success: con-
equipment fitted in vehicles or the way in          Generally, no effort or expense is spared on          spicuity, legibility, comprehensibility and
which the information is broadcast.                 control room, vehicle detection, surveillance,        credibility. Conspicuity of a VMS is governed
   Second, all drivers receive the same infor-      etc., and processing the data that has been           by considerations relating to its visibility
mation in a consistent format which is rele-        collected. All this is basically for the benefit of   and environment:
vant to the situation. Finally, the operator can    the road operator to understand what is hap-            • Sign height;
be confident that the majority of drivers will      pening on the network. This can make the                • Road geometry;
read the message and take appropriate action        operator data rich, but information poor.               • Location;
and, from a safety and legal point of view, he      That is to say there are mountains of data, but         • Viewing angle;
will be seen to have acted reasonably.              very little information extracted for the               • Alignment;
                                                                                                            • Clear field of vision;
                                                                                                            • Free from clutter and distraction;
                                                                                                            • Visible to the driver;
                                                                                                            • Flashing lanterns to attract attention;
                                                                                                            • Legibility.
                                                                                                          Aspects affecting legibility include:
                                                                                                            • Things the driver can recognise;
                                                                                                            • Distance at which the message can be
                                                                                                            • Approach speed;
                                                                                                            • Character height;
                                                                                                            • Character font and style;
                                                                                                            • Pixel, character, word and line spacing
                                                                                                            •Luminance (contrast) ratio and sign
                                                                                                          Comprehensibility concerns the driver’s abil-
                                                                                                          ity to read, comprehend, assimilate and act
                                                                                                          on the information displayed. Human factors
                                                                                                          come into play here, such as age, background,
                                                                                                          skill and language. The operator can improve
                                                                                                          the situation by using consistent formats, a
                                                                                                          clear geographic description, concise instruc-
                                                                                                          tion and providing adequate time and dis-
                                                                                                          tance for the message to be read.
                                                                                                              The credibility of driver information is
                                                                                                          the summation of the criteria with the addi-
                                                                                                          tional consideration of the management of
                                                                                                          the overall traffic system, institutional
                                                                                                          strategic and tactical objectives, reliability
                                                                                                          and accuracy of messages and the optical
                                                                                                          performance of the VMS. Finally, when
                                                                                                          all the criteria have been considered, it is
                                                                                                          the optical performance and accuracy of
                                                                                                          messages that impacts the behaviour of driv-
                                                                                                          ers. If the driver cannot read the message
                                                                                                          and it is wrong for prevailing conditions it
                                                                                                          will be ignored and once driver confidence
                                                                                                          is lost, it can be years before a credible
FIGURE 2: MS3 STRATEGIC dRIVER INFORMATION SIGN                                                           reputation is restored.

TRAFFIC TECHNOLOGY INTERNATIONAL 2005                                                                                                               111

FIGURE 3: BEAM AREAS                                                               FIGURE 5: VIEWING ANd ALIGNMENT

                                                   Electrotechnical Standards Committee) com-          cLaSS act
                                                   prising national standards bodies of the 28         The standard draws attention to effective
                                                   CEN members on 15 March 2005.                       class combination in Annex E.5 which is
                                                       It has three parts: Product standard,           quoted verbatim: “For effective use the cor-
                                                   initial type testing and factory production         rect selection of combinations of luminance,
                                                   control. The objective is to provide a set          luminance ratio and beam width is essential.
                                                   of functional requirements that are not             For example, the selection of the highest
                                                   technology specific and, when followed by           (brightest) luminance class L3 for long view-
                                                   designers and manufacturers, will result            ing distance means, that in practice a narrow
                                                   in a product of good quality and perform-           beam width is only required; this means, that
                                                   ance. The net result will be enhanced safety        the available light has a distribution to cover
                                                   because mandatory and advisory messages             the lane width at a significant distance from
                                                   will be displayed on signs that are both            the sign.
FIGURE 4: 3d BEAM WIdTHS                           legible and reliable.                                   “Wider beam widths distribute the light
                                                       The standard defines the parameters of          laterally over a larger angle; and consequently
   At the ROADS 05 conference in October           a VMS by visual and physical performance,           have a shorter viewing distance. Typically to
2005, Denise Plumpton, Director of Informa-        as shown in Table 1. As a designer and manu-        maintain the brightness between beam width
tion of the Highways Agency in England,            facturer of variable message signs, I have al-      classes B1 and B7 the luminance required for
encapsulated the idea of credibility in a          ways had a concern that certain aspects of          B7 class would be approximately 24 times
presentation when she said that to influence       EN12966 could, even with the best inten-            the B1 class. Consequently for the shorter
drivers, information has to be TRUE, mean-         tions, be misinterpreted by individuals             viewing distance the luminance required is
ing: Trusted, Reliable, Useful and Effective.      charged with responsibility for selecting the       less, therefore for wider beam width classes it
                                                   performance classes for visual and physical         is only necessary to select the lower lumi-
Standard meaSUre                                   performance, chapters seven and eight of the        nance classes.
Within Europe VMS had developed country            document respectively.                                  “Because the luminance ratio is linked to
by country with different performance and              The visual and physical parameters offer        luminance for any particular sign or color,
quality standards. To ensure consistency           more than 6,000 combinations. The particu-          the selection of luminance ratio class to be
a technical committee under the auspices           lar sections on which I shall concentrate in        used depends on the luminance and there-
of CEN/ TC226 was established in 1994              the remainder of this article include beam          fore on the beam width. For wider beam
to prepare a standard.                             width, horizontal and vertical alignment and,       width classes it is also only necessary to select
   The outcome, European Standard for              briefly, environmental considerations.              the lower luminance ratio classes.”
Variable Message Signs, EN 12966, is the               If you select the appropriate combination           Well now, did you all understand that?
culmination of many years of diligent effort       of classes for a given application you will ob-     Quite a lot of it I suspect, but included here
by representatives of industry, governments        tain an economical VMS with good reliable           are some tables to support it. Incidentally,
and testing authorities from across the conti-     performance. If you select inappropriate            seven beam width classes B1 to B7 are given
nent. The standard was approved by CEN             classes (especially beam width) you might get       in Table six of the proposed standard. Sets of
(Committee Electrotechnical Normative/             a shock when you see the price...                   three test angles are used to determine the
                                                                                                       various beam width classes.
                                                                                                           To understand this table more graphically
   Table 1: Visual and physical performance                                                            Figure 3 shows the relationship between
                                                                                                       classes. If B1 is considered as one unit then it
   PHOTOMETRIC PARAMETER         CLASS dESIGNATION            REMARKS                                  is easier to see how B7 is 24 times B1.It shows
   Colour                        C1, C2                       C2 is the more restrictive               the relationship between classes. If B1 is con-
   Luminance (La)                L1, L2, L3, L3(*)            L3 has the highest luminance, (*) for    sidered as one unit, then it is easier to see
                                                              specific situations                      how B7 is 24 times B1.
   Luminance (La)                L1(T), L2(T), L3(T)          These classes are for tunnel use             The standard actually states that B7 is only
   Luminance ratio (LR)          R1, R2, R3                   R3 has the highest luminance ratio
                                                                                                       for specific applications. If we consider that
   Beam width                    B1, B2, B3, B4, B5, B6, B7   B7 has the widest beam
                                                                                                       B1 is the choice for, say, a high speed two lane
   PHYSICAL PERFORMANCE                                                                                and safety lane motorway or expressway then
   ENVIRONMENTAL PARAMETER       CLASS dESIGNATION            REMARKS                                  B3 and B4 could be applied to three, four and
   Temperature                   T1, T2, T3                                                            five lane highways and B5 and B6 would
   Pollution                     D1, D2, D3, D4               D4 is the most restrictive
   Protection                    P1, P2, P3                   P3 is the most restrictive
                                                                                                       most likely be the selection for urban applica-
                                                                                                       tions where approach speed is much slower.
                                                                                                       B7 is for special applications and must take

112                                                                                                      TRAFFIC TECHNOLOGY INTERNATIONAL 2005

   Table 2: Beam width class
   B1                     -5 / 0                       +5 / 0       0 / -5
   B2                     -7 / 0                       +7 / 0       0 / -5
   B3                     -10 / 0                      +10 / 0      0 / -5
   B4                     -10 / 0                      +10 / 0      0 / -10
   B5                     -15 / 0                      +15 / 0      0 / -5
   B6                     -15 / 0                      +15 / 0      0 / -10
   B7                     -30 / 0                      +30 / 0      0 / -20

“the driver has no knowledge of
the unseen system and judges the
credibility of the system by the
information displayed”                                                                                   FIGURE 6: VARIABLE MESSAGE SIGNS SUPPLIEd
                                                                                                         FOR TRAFFIC CONTROL AROUNd THE ATHENS

cognisance of exceedingly slow approach                   If distance is equated to approach speed       there is a temperature class to cope and
speeds where wide angle legibility is impor-          by noting that at 110k/h a vehicle travels         manufacturers ready to design and build.
tant such as the approach to car parks and for        30.6m/s, the driver has very little time to read      The Ingress Protection Class or IP rating
cyclists and pedestrians. Frankly it is hard to       the message once he or she is close to the         as it is more commonly known was pre-
know where you would use B7. Three di-                sign. It is much better to concentrate on long     established and definitions can be found in
mensionally the effect of horizontal and verti-       distance legibility by selecting the appropri-     EN 60529 category two.
cal beam widths can be seen dramatically by           ate character height and optical performance
considering classes B1, B3 and B7.                    than to encourage drivers to crane their necks     effIcIency
    The dramatic difference between the class-        to read the message in the last few millisec-      Is there anyone reading this article who has
es can be seen in the three-dimensional repre-        onds. In urban applications wider beam             not heard the arguments supporting global
sentation of beam widths in Figure 4. It can be       widths are necessary where smaller character       warming and the pleas to reduce energy
observed that B1and B3 are suitable for a high        sizes are deployed and approach speeds             consumption? So what has that got to do
speed roads, B1 for two or three lane and B3          are slower.                                        with variable message signs? Quite a lot.
for three to five lanes. B7 horizontal beam               By adjusting the sign alignment horizontally   By selecting the correct beam width for your
width is too wide and simply wastes emitted           and vertically the spread of the beam can be       application you can have an effect on the en-
light in areas where it is of no value to drivers.    optimised to any given location and road lay-      ergy consumption of the VMS. Insisting on
The vertical angle determines the distance            out. Small adjustments to the horizontal and       beam widths that are too wide for the loca-
from the sign at which the emitted light touch-       vertical alignments make a big difference to the   tion costs money, wastes energy and creates
es the road surface and beyond which the              distances at which messages are legible.           light pollution. For a long range viewing ap-
message begins to cut out. In the diagram the             The correct alignment of a VMS in its loca-    plication of, say, 300 metres where a 400 mm
cantilever mounted sign is vertical and has its       tion has a major affect on achieving the con-      high character is required, Class B1 is proba-
central point seven metres above the road sur-        spicuity and legibility criteria of a successful   bly the right choice depending on the number
face. Therefore the approximate distances for         deployment. It is also worth noting that Eu-       of lanes to be covered. If you select B7 just to
the three classes are shown below:                    rope has a wide range of climatic conditions       be on the safe side and to cover every contin-
                                                      from the Artic north to the hot Mediterrane-       gency you will require 24 times the light out-
                                                      an. The temperature classes take this into         put and waste 23 times or 96 per cent of the
   Table 3: distance classification                   account.                                           light output. Can you and your clients really
                                                          Clearly, the vast majority of applications     afford it?
                             (METRES)                 will fall into Class T1 and although T3 covers         VMS Limited’s Rigel LED technology has
   B1       5 up    0 down   80                       northernmost climates it is not expected that      been designed with unique parabolic optical
   B3       10 up   0 down   40                       many signs with this temperature class will        devices that employ the principle of total
   B7       20 up   0 down   20                       be installed because of few roads and sparse       internal reflection to produce extremely
                                                      populations but, where VMS are needed,             accurate beam widths, optical efficacy and
                                                                                                         consequently exceptionally low energy
                                                                                                         costs. I strongly believe that EN 12966 has
   Table 4: Viewing distance and read times                                                              much wider application than just within
                                                                                                         Europe and that road authorities, private
   HEIGHT    VIEWING       REAd TIME IN SECONdS                                                          developers, operators, consultants and
   MM        dIST M 40 KPH 50 KPH  60 KPH 80 KPH                  100 KPH 110 KPH                        designers throughout the world should con-
                                                                                                         sider this Standard for their future variable
   100           60        5.5       4.3       3.5       3        2         -         uRBan
                                                                                                         message sign requirements. n
   160           90        8.2       6.5       5.4       4        3
   200           120       10.9      8.6       7.2       5.5      4.5       4
                                                                                                         The auThoR is The DePuTy ChaiRman of Vms
   240           150       13.6      10.8      9.0       6.8      5.6       4.9
                                                                                                         LimiTeD anD siTs on The CommiTTee foR euRo-
   320           200       18.2      14.4      12.0      9.1      7.4       6.5                          Pean sTanDaRDs foR VaRiaBLe message signs.
   400           300       27.3      21.6      18.0      13.6     11.1      9.8       inTeR uRBan        The Views exPResseD in This aRTiCLe aRe his PeR-
                                                                                                         sonaL Views anD Do noT neCessaRiLy RefLeCT
                                                                                                         The View of The CommiTTee

TRAFFIC TECHNOLOGY INTERNATIONAL 2005                                                                                                               113

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