+-----------+----------------------------------------------------------+
| ![](m     | **Impact of Data Link Technology on Railroad Dispatching |
| edia/imag | Operations**                                             |
| e1.wmf){w |                                                          |
| idth="2.9 |                                                          |
| 895833333 |                                                          |
| 333335in" |                                                          |
| height="  |                                                          |
| 1.4486111 |                                                          |
| 11111111i |                                                          |
| n"}![](me |                                                          |
| dia/image |                                                          |
| 2.wmf){wi |                                                          |
| dth="0.46 |                                                          |
| 111111111 |                                                          |
| 111114in" |                                                          |
| hei       |                                                          |
| ght="0.50 |                                                          |
| 347222222 |                                                          |
| 22222in"} |                                                          |
|           |                                                          |
| U.S.      |                                                          |
| D         |                                                          |
| epartment |                                                          |
|           |                                                          |
| of        |                                                          |
| Trans     |                                                          |
| portation |                                                          |
|           |                                                          |
| **Federal |                                                          |
| R         |                                                          |
| ailroad** |                                                          |
|           |                                                          |
| **Adminis |                                                          |
| tration** |                                                          |
+-----------+----------------------------------------------------------+

+----------------------+-----------------------------------------------+
| Office of Research   | U.S. Department of Transportation             |
|                      |                                               |
| and Development      | Research and Special Programs Administration  |
|                      |                                               |
| Washington, DC 20590 | John A. Volpe National Transportation Systems |
|                      | Center                                        |
|                      |                                               |
|                      | Cambridge, MA 02142                           |
+----------------------+-----------------------------------------------+

![](media/image3.png){width="5.5in" height="3.251388888888889in"}

+------------------------+--------------------+------------------------+
| DOT/FRA/ORD-04/11      | > Final Report     | This document is       |
|                        | >                  | available to the       |
|                        | > October 2004     |                        |
|                        |                    | public through the     |
|                        |                    | National Technical     |
|                        |                    |                        |
|                        |                    | Information Service,   |
|                        |                    | Springfield, VA 22161  |
|                        |                    |                        |
|                        |                    | This document is also  |
|                        |                    | available on           |
|                        |                    |                        |
|                        |                    | the FRA website at     |
|                        |                    | www.fra.dot.gov        |
+------------------------+--------------------+------------------------+

+-----------------------------------------------------------------------+
| > Notice                                                              |
|                                                                       |
| This document is disseminated under the sponsorship of the Department |
| of Transportation in the interest of information exchange. The United |
| States Government assumes no liability for its contents or use        |
| thereof.                                                              |
+-----------------------------------------------------------------------+
|                                                                       |
+-----------------------------------------------------------------------+
| > Notice                                                              |
|                                                                       |
| The United States Government does not endorse products or             |
| manufacturers. Trade or manufacturers' names appear herein solely     |
| because they are considered essential to the objective of this        |
| report.                                                               |
+-----------------------------------------------------------------------+

+------------------+---+--------------+---+-------+---+---+--------------+
| **Report         |   |              |   |       | F |   |              |
| Documentation    |   |              |   |       | o |   |              |
| page**           |   |              |   |       | r |   |              |
|                  |   |              |   |       | m |   |              |
|                  |   |              |   |       | A |   |              |
|                  |   |              |   |       | p |   |              |
|                  |   |              |   |       | p |   |              |
|                  |   |              |   |       | r |   |              |
|                  |   |              |   |       | o |   |              |
|                  |   |              |   |       | v |   |              |
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|                  |   |              |   |       | d |   |              |
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|                  |   |              |   |       | O |   |              |
|                  |   |              |   |       | M |   |              |
|                  |   |              |   |       | B |   |              |
|                  |   |              |   |       | N |   |              |
|                  |   |              |   |       | o |   |              |
|                  |   |              |   |       | . |   |              |
|                  |   |              |   |       | 0 |   |              |
|                  |   |              |   |       | 7 |   |              |
|                  |   |              |   |       | 0 |   |              |
|                  |   |              |   |       | 4 |   |              |
|                  |   |              |   |       | - |   |              |
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|                  |   |              |   |       | 1 |   |              |
|                  |   |              |   |       | 8 |   |              |
|                  |   |              |   |       | 8 |   |              |
+------------------+---+--------------+---+-------+---+---+--------------+
| Public reporting |   |              |   |       |   |   |              |
| burden for this  |   |              |   |       |   |   |              |
| collection of    |   |              |   |       |   |   |              |
| information is   |   |              |   |       |   |   |              |
| estimated to     |   |              |   |       |   |   |              |
| average 1 hour   |   |              |   |       |   |   |              |
| per response,    |   |              |   |       |   |   |              |
| including the    |   |              |   |       |   |   |              |
| time for         |   |              |   |       |   |   |              |
| reviewing        |   |              |   |       |   |   |              |
| instructions,    |   |              |   |       |   |   |              |
| searching        |   |              |   |       |   |   |              |
| existing data    |   |              |   |       |   |   |              |
| sources,         |   |              |   |       |   |   |              |
| gathering and    |   |              |   |       |   |   |              |
| maintaining the  |   |              |   |       |   |   |              |
| data needed and  |   |              |   |       |   |   |              |
| completing and   |   |              |   |       |   |   |              |
| reviewing the    |   |              |   |       |   |   |              |
| collection of    |   |              |   |       |   |   |              |
| information.     |   |              |   |       |   |   |              |
| Send comments    |   |              |   |       |   |   |              |
| regarding this   |   |              |   |       |   |   |              |
| burden estimate  |   |              |   |       |   |   |              |
| or any aspects   |   |              |   |       |   |   |              |
| of this          |   |              |   |       |   |   |              |
| collection of    |   |              |   |       |   |   |              |
| information ,    |   |              |   |       |   |   |              |
| including        |   |              |   |       |   |   |              |
| suggestions for  |   |              |   |       |   |   |              |
| reducing this    |   |              |   |       |   |   |              |
| burden to        |   |              |   |       |   |   |              |
| Washington       |   |              |   |       |   |   |              |
| Headquarters     |   |              |   |       |   |   |              |
| Service,         |   |              |   |       |   |   |              |
| Directorate for  |   |              |   |       |   |   |              |
| information      |   |              |   |       |   |   |              |
| Operations and   |   |              |   |       |   |   |              |
| Reports. 1215    |   |              |   |       |   |   |              |
| Jefferson Davis  |   |              |   |       |   |   |              |
| Highway, Suite   |   |              |   |       |   |   |              |
| 1204, Arlington, |   |              |   |       |   |   |              |
| VA. 222202-4302, |   |              |   |       |   |   |              |
| and to the       |   |              |   |       |   |   |              |
| Office of        |   |              |   |       |   |   |              |
| Management and   |   |              |   |       |   |   |              |
| Budget,          |   |              |   |       |   |   |              |
| Paperwork        |   |              |   |       |   |   |              |
| Reduction        |   |              |   |       |   |   |              |
| Project          |   |              |   |       |   |   |              |
| (0704-0188),     |   |              |   |       |   |   |              |
| Washington, DC   |   |              |   |       |   |   |              |
| 20503.           |   |              |   |       |   |   |              |
+------------------+---+--------------+---+-------+---+---+--------------+
| 1\. Agency Use   |   | 2.  Report   |   | 3.  R |   |   |              |
| Only (*Leave     |   |     Date     |   | EPORT |   |   |              |
| blank*)          |   |              |   |       |   |   |              |
|                  |   | October 2004 |   |  TYPE |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |   AND |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   | DATES |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |    CO |   |   |              |
|                  |   |              |   | VERED |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   | Final |   |   |              |
|                  |   |              |   | R     |   |   |              |
|                  |   |              |   | eport |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   | Sept  |   |   |              |
|                  |   |              |   | ember |   |   |              |
|                  |   |              |   | 1     |   |   |              |
|                  |   |              |   | 998 - |   |   |              |
|                  |   |              |   | Oc    |   |   |              |
|                  |   |              |   | tober |   |   |              |
|                  |   |              |   | 1999  |   |   |              |
+------------------+---+--------------+---+-------+---+---+--------------+
| 4.  Title and    |   |              |   |       | 5 |   |              |
|     subtitle     |   |              |   |       | . |   |              |
|                  |   |              |   |       |   |   |              |
| Impact of Data   |   |              |   |       |   |   |              |
| Link Technology  |   |              |   |       | F |   |              |
| on Railroad      |   |              |   |       | U |   |              |
| Dispatching      |   |              |   |       | N |   |              |
| Operations       |   |              |   |       | D |   |              |
|                  |   |              |   |       | I |   |              |
|                  |   |              |   |       | N |   |              |
|                  |   |              |   |       | G |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       | N |   |              |
|                  |   |              |   |       | U |   |              |
|                  |   |              |   |       | M |   |              |
|                  |   |              |   |       | B |   |              |
|                  |   |              |   |       | E |   |              |
|                  |   |              |   |       | R |   |              |
|                  |   |              |   |       | S |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       | R |   |              |
|                  |   |              |   |       | 2 |   |              |
|                  |   |              |   |       | 1 |   |              |
|                  |   |              |   |       | 0 |   |              |
|                  |   |              |   |       | 3 |   |              |
|                  |   |              |   |       | / |   |              |
|                  |   |              |   |       | R |   |              |
|                  |   |              |   |       | R |   |              |
|                  |   |              |   |       | 2 |   |              |
|                  |   |              |   |       | 0 |   |              |
|                  |   |              |   |       | 4 |   |              |
+------------------+---+--------------+---+-------+---+---+--------------+
| 6.  AUTHOR(S)    |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
| Nicolas Malsch,  |   |              |   |       |   |   |              |
| Thomas Sheridan, |   |              |   |       |   |   |              |
| and Jordan       |   |              |   |       |   |   |              |
| Multer           |   |              |   |       |   |   |              |
+------------------+---+--------------+---+-------+---+---+--------------+
| 7.  PERFORMING   |   |              |   |       | 8 |   |              |
|     ORGANIZATION |   |              |   |       | . |   |              |
|     NAME(S) AND  |   |              |   |       |   |   |              |
|     ADDRESS(ES)  |   |              |   |       |   |   |              |
|                  |   |              |   |       | P |   |              |
| U.S. Department  |   |              |   |       | E |   |              |
| of               |   |              |   |       | R |   |              |
| Transportation   |   |              |   |       | F |   |              |
|                  |   |              |   |       | O |   |              |
| Research and     |   |              |   |       | R |   |              |
| Special Programs |   |              |   |       | M |   |              |
| Administration   |   |              |   |       | I |   |              |
|                  |   |              |   |       | N |   |              |
| John A. Volpe    |   |              |   |       | G |   |              |
| National         |   |              |   |       |   |   |              |
| Transportation   |   |              |   |       |   |   |              |
| Systems Center   |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
| Cambridge, MA.   |   |              |   |       | O |   |              |
| 02142            |   |              |   |       | R |   |              |
|                  |   |              |   |       | G |   |              |
|                  |   |              |   |       | A |   |              |
|                  |   |              |   |       | N |   |              |
|                  |   |              |   |       | I |   |              |
|                  |   |              |   |       | Z |   |              |
|                  |   |              |   |       | A |   |              |
|                  |   |              |   |       | T |   |              |
|                  |   |              |   |       | I |   |              |
|                  |   |              |   |       | O |   |              |
|                  |   |              |   |       | N |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       | D |   |              |
|                  |   |              |   |       | O |   |              |
|                  |   |              |   |       | T |   |              |
|                  |   |              |   |       | - |   |              |
|                  |   |              |   |       | V |   |              |
|                  |   |              |   |       | N |   |              |
|                  |   |              |   |       | T |   |              |
|                  |   |              |   |       | S |   |              |
|                  |   |              |   |       | C |   |              |
|                  |   |              |   |       | - |   |              |
|                  |   |              |   |       | F |   |              |
|                  |   |              |   |       | R |   |              |
|                  |   |              |   |       | A |   |              |
|                  |   |              |   |       | - |   |              |
|                  |   |              |   |       | 0 |   |              |
|                  |   |              |   |       | 4 |   |              |
|                  |   |              |   |       | - |   |              |
|                  |   |              |   |       | 0 |   |              |
|                  |   |              |   |       | 4 |   |              |
+------------------+---+--------------+---+-------+---+---+--------------+
| 9.  SPONS        |   |              |   |       | 1 |   |              |
| ORING/MONITORING |   |              |   |       | 0 |   |              |
|     AGENCY       |   |              |   |       | . |   |              |
|     NAME(S) AND  |   |              |   |       |   |   |              |
|     ADDRESS(ES)  |   |              |   |       | S |   |              |
|                  |   |              |   |       | P |   |              |
| U.S. Department  |   |              |   |       | O |   |              |
| of               |   |              |   |       | N |   |              |
| Transportation   |   |              |   |       | S |   |              |
|                  |   |              |   |       | O |   |              |
| Federal Railroad |   |              |   |       | R |   |              |
| Administration   |   |              |   |       | I |   |              |
|                  |   |              |   |       | N |   |              |
| Office of        |   |              |   |       | G |   |              |
| Research and     |   |              |   |       | / |   |              |
| Development,     |   |              |   |       | M |   |              |
| Mail Stop 20     |   |              |   |       | O |   |              |
|                  |   |              |   |       | N |   |              |
| 1120 Vermont     |   |              |   |       | I |   |              |
| Ave, NW          |   |              |   |       | T |   |              |
|                  |   |              |   |       | O |   |              |
| Washington, DC.  |   |              |   |       | R |   |              |
| 20590            |   |              |   |       | I |   |              |
|                  |   |              |   |       | N |   |              |
|                  |   |              |   |       | G |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       | A |   |              |
|                  |   |              |   |       | G |   |              |
|                  |   |              |   |       | E |   |              |
|                  |   |              |   |       | N |   |              |
|                  |   |              |   |       | C |   |              |
|                  |   |              |   |       | Y |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       | R |   |              |
|                  |   |              |   |       | E |   |              |
|                  |   |              |   |       | P |   |              |
|                  |   |              |   |       | O |   |              |
|                  |   |              |   |       | R |   |              |
|                  |   |              |   |       | T |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       | N |   |              |
|                  |   |              |   |       | U |   |              |
|                  |   |              |   |       | M |   |              |
|                  |   |              |   |       | B |   |              |
|                  |   |              |   |       | E |   |              |
|                  |   |              |   |       | R |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       | D |   |              |
|                  |   |              |   |       | O |   |              |
|                  |   |              |   |       | T |   |              |
|                  |   |              |   |       | / |   |              |
|                  |   |              |   |       | F |   |              |
|                  |   |              |   |       | R |   |              |
|                  |   |              |   |       | A |   |              |
|                  |   |              |   |       | / |   |              |
|                  |   |              |   |       | O |   |              |
|                  |   |              |   |       | R |   |              |
|                  |   |              |   |       | D |   |              |
|                  |   |              |   |       | - |   |              |
|                  |   |              |   |       | 0 |   |              |
|                  |   |              |   |       | 4 |   |              |
|                  |   |              |   |       | / |   |              |
|                  |   |              |   |       | 1 |   |              |
|                  |   |              |   |       | 1 |   |              |
+------------------+---+--------------+---+-------+---+---+--------------+
| 1                |   |              |   |       |   |   |              |
| 1. SUPPLEMENTARY |   |              |   |       |   |   |              |
|     NOTES        |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
+------------------+---+--------------+---+-------+---+---+--------------+
| 12a.             |   |              |   |       | 1 |   |              |
| DISTRIBUT        |   |              |   |       | 2 |   |              |
| ION/AVAILABILITY |   |              |   |       | b |   |              |
| STATEMENT        |   |              |   |       | . |   |              |
|                  |   |              |   |       | D |   |              |
| This document is |   |              |   |       | I |   |              |
| available to the |   |              |   |       | S |   |              |
| public through   |   |              |   |       | T |   |              |
| the National     |   |              |   |       | R |   |              |
| Technical        |   |              |   |       | I |   |              |
| Information      |   |              |   |       | B |   |              |
| Service,         |   |              |   |       | U |   |              |
| Springfield, VA  |   |              |   |       | T |   |              |
| 22161. This      |   |              |   |       | I |   |              |
| document is also |   |              |   |       | O |   |              |
| available on the |   |              |   |       | N |   |              |
| FRA web site at  |   |              |   |       | C |   |              |
| www.fra.dot.gov. |   |              |   |       | O |   |              |
|                  |   |              |   |       | D |   |              |
|                  |   |              |   |       | E |   |              |
+------------------+---+--------------+---+-------+---+---+--------------+
| 13. ABSTRACT     |   |              |   |       |   |   |              |
|     (Maximum 200 |   |              |   |       |   |   |              |
|     words)       |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
| This study       |   |              |   |       |   |   |              |
| examined data    |   |              |   |       |   |   |              |
| link             |   |              |   |       |   |   |              |
| communication as |   |              |   |       |   |   |              |
| an alternative   |   |              |   |       |   |   |              |
| channel to voice |   |              |   |       |   |   |              |
| radio for        |   |              |   |       |   |   |              |
| railroad         |   |              |   |       |   |   |              |
| dispatchers. The |   |              |   |       |   |   |              |
| goal was to      |   |              |   |       |   |   |              |
| compare how data |   |              |   |       |   |   |              |
| link affected    |   |              |   |       |   |   |              |
| performance      |   |              |   |       |   |   |              |
| compared to      |   |              |   |       |   |   |              |
| voice radio only |   |              |   |       |   |   |              |
| communications   |   |              |   |       |   |   |              |
| on measures      |   |              |   |       |   |   |              |
| related to       |   |              |   |       |   |   |              |
| safety,          |   |              |   |       |   |   |              |
| productivity,    |   |              |   |       |   |   |              |
| communication    |   |              |   |       |   |   |              |
| efficiency, and  |   |              |   |       |   |   |              |
| situation        |   |              |   |       |   |   |              |
| awareness. A     |   |              |   |       |   |   |              |
| data link system |   |              |   |       |   |   |              |
| with two         |   |              |   |       |   |   |              |
| addressing       |   |              |   |       |   |   |              |
| options was      |   |              |   |       |   |   |              |
| compared to      |   |              |   |       |   |   |              |
| radio. The       |   |              |   |       |   |   |              |
| discrete message |   |              |   |       |   |   |              |
| capability       |   |              |   |       |   |   |              |
| enabled the      |   |              |   |       |   |   |              |
| dispatcher to    |   |              |   |       |   |   |              |
| send a message   |   |              |   |       |   |   |              |
| to one           |   |              |   |       |   |   |              |
| individual at a  |   |              |   |       |   |   |              |
| time. The        |   |              |   |       |   |   |              |
| broadcast        |   |              |   |       |   |   |              |
| message          |   |              |   |       |   |   |              |
| capability       |   |              |   |       |   |   |              |
| enabled the      |   |              |   |       |   |   |              |
| dispatcher to    |   |              |   |       |   |   |              |
| send a single    |   |              |   |       |   |   |              |
| message to       |   |              |   |       |   |   |              |
| multiple         |   |              |   |       |   |   |              |
| recipients. The  |   |              |   |       |   |   |              |
| experiment was   |   |              |   |       |   |   |              |
| run on a         |   |              |   |       |   |   |              |
| h                |   |              |   |       |   |   |              |
| uman-in-the-loop |   |              |   |       |   |   |              |
| railroad         |   |              |   |       |   |   |              |
| dispatcher       |   |              |   |       |   |   |              |
| simulator.       |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
| Overall, data    |   |              |   |       |   |   |              |
| link proved      |   |              |   |       |   |   |              |
| superior to the  |   |              |   |       |   |   |              |
| voice radio      |   |              |   |       |   |   |              |
| environment, in  |   |              |   |       |   |   |              |
| terms of safety. |   |              |   |       |   |   |              |
| Safety of        |   |              |   |       |   |   |              |
| maintenance      |   |              |   |       |   |   |              |
| workers was      |   |              |   |       |   |   |              |
| improved by both |   |              |   |       |   |   |              |
| data link        |   |              |   |       |   |   |              |
| systems while    |   |              |   |       |   |   |              |
| train safety was |   |              |   |       |   |   |              |
| improved only    |   |              |   |       |   |   |              |
| for broadcast    |   |              |   |       |   |   |              |
| messages. No     |   |              |   |       |   |   |              |
| increase in      |   |              |   |       |   |   |              |
| dispatching      |   |              |   |       |   |   |              |
| productivity     |   |              |   |       |   |   |              |
| (train and track |   |              |   |       |   |   |              |
| maintenance) was |   |              |   |       |   |   |              |
| observed with    |   |              |   |       |   |   |              |
| data link. For   |   |              |   |       |   |   |              |
| communication    |   |              |   |       |   |   |              |
| efficiency, the  |   |              |   |       |   |   |              |
| results depended |   |              |   |       |   |   |              |
| upon message     |   |              |   |       |   |   |              |
| complexity.      |   |              |   |       |   |   |              |
| Dispatchers      |   |              |   |       |   |   |              |
| spent less time  |   |              |   |       |   |   |              |
| exchanging       |   |              |   |       |   |   |              |
| simple messages  |   |              |   |       |   |   |              |
| with voice       |   |              |   |       |   |   |              |
| radio.           |   |              |   |       |   |   |              |
| Conversely,      |   |              |   |       |   |   |              |
| dispatchers      |   |              |   |       |   |   |              |
| exchanged        |   |              |   |       |   |   |              |
| complex messages |   |              |   |       |   |   |              |
| more quickly in  |   |              |   |       |   |   |              |
| the data link    |   |              |   |       |   |   |              |
| environment. The |   |              |   |       |   |   |              |
| differences in   |   |              |   |       |   |   |              |
| communication    |   |              |   |       |   |   |              |
| efficiency as a  |   |              |   |       |   |   |              |
| function of      |   |              |   |       |   |   |              |
| message          |   |              |   |       |   |   |              |
| complexity can   |   |              |   |       |   |   |              |
| be attributed to |   |              |   |       |   |   |              |
| the type of      |   |              |   |       |   |   |              |
| interface:       |   |              |   |       |   |   |              |
| visual or        |   |              |   |       |   |   |              |
| auditory.        |   |              |   |       |   |   |              |
+------------------+---+--------------+---+-------+---+---+--------------+
| 14. SUBJECT      |   |              |   |       |   | 1 |              |
|     TERMS        |   |              |   |       |   | 5 |              |
|                  |   |              |   |       |   | . |              |
|     cognitive    |   |              |   |       |   |   |              |
|     task         |   |              |   |       |   | N |              |
|     analysis,    |   |              |   |       |   | U |              |
|     radio        |   |              |   |       |   | M |              |
|                  |   |              |   |       |   | B |              |
|  communications, |   |              |   |       |   | E |              |
|     data link,   |   |              |   |       |   | R |              |
|                  |   |              |   |       |   |   |              |
| decision-making, |   |              |   |       |   |   |              |
|     displays,    |   |              |   |       |   |   |              |
|     intelligent  |   |              |   |       |   |   |              |
|     railroad     |   |              |   |       |   | O |              |
|     systems,     |   |              |   |       |   | F |              |
|     railroad     |   |              |   |       |   |   |              |
|     dispatcher,  |   |              |   |       |   |   |              |
|     track        |   |              |   |       |   |   |              |
|     allocation,  |   |              |   |       |   |   |              |
|     train        |   |              |   |       |   | P |              |
|     routing      |   |              |   |       |   | A |              |
|                  |   |              |   |       |   | G |              |
|                  |   |              |   |       |   | E |              |
|                  |   |              |   |       |   | S |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   | 7 |              |
|                  |   |              |   |       |   | 6 |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   | 1 |              |
|                  |   |              |   |       |   | 6 |              |
|                  |   |              |   |       |   | . |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   | P |              |
|                  |   |              |   |       |   | R |              |
|                  |   |              |   |       |   | I |              |
|                  |   |              |   |       |   | C |              |
|                  |   |              |   |       |   | E |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   | C |              |
|                  |   |              |   |       |   | O |              |
|                  |   |              |   |       |   | D |              |
|                  |   |              |   |       |   | E |              |
+------------------+---+--------------+---+-------+---+---+--------------+
| 17. SECURITY     | 1 |              | 1 |       |   |   | LIMITATION   |
|                  | 8 |              | 9 |       |   |   | OF ABSTRACT  |
|   CLASSIFICATION | . |              | . |       |   |   |              |
|     OF REPORT    |   |              |   |       |   |   | Unclassified |
|                  | S |              | S |       |   |   |              |
|     Unclassified | E |              | E |       |   |   |              |
|                  | C |              | C |       |   |   |              |
|                  | U |              | U |       |   |   |              |
|                  | R |              | R |       |   |   |              |
|                  | I |              | I |       |   |   |              |
|                  | T |              | T |       |   |   |              |
|                  | Y |              | Y |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  | C |              | C |       |   |   |              |
|                  | L |              | L |       |   |   |              |
|                  | A |              | A |       |   |   |              |
|                  | S |              | S |       |   |   |              |
|                  | S |              | S |       |   |   |              |
|                  | I |              | I |       |   |   |              |
|                  | F |              | F |       |   |   |              |
|                  | I |              | I |       |   |   |              |
|                  | C |              | C |       |   |   |              |
|                  | A |              | A |       |   |   |              |
|                  | T |              | T |       |   |   |              |
|                  | I |              | I |       |   |   |              |
|                  | O |              | O |       |   |   |              |
|                  | N |              | N |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  | O |              | O |       |   |   |              |
|                  | F |              | F |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  | T |              | A |       |   |   |              |
|                  | H |              | B |       |   |   |              |
|                  | I |              | S |       |   |   |              |
|                  | S |              | T |       |   |   |              |
|                  |   |              | R |       |   |   |              |
|                  |   |              | A |       |   |   |              |
|                  |   |              | C |       |   |   |              |
|                  |   |              | T |       |   |   |              |
|                  | P |              |   |       |   |   |              |
|                  | A |              |   |       |   |   |              |
|                  | G |              |   |       |   |   |              |
|                  | E |              |   |       |   |   |              |
|                  |   |              |   |       |   |   |              |
|                  |   |              | U |       |   |   |              |
|                  |   |              | n |       |   |   |              |
|                  |   |              | c |       |   |   |              |
|                  |   |              | l |       |   |   |              |
|                  | U |              | a |       |   |   |              |
|                  | n |              | s |       |   |   |              |
|                  | c |              | s |       |   |   |              |
|                  | l |              | i |       |   |   |              |
|                  | a |              | f |       |   |   |              |
|                  | s |              | i |       |   |   |              |
|                  | s |              | e |       |   |   |              |
|                  | i |              | d |       |   |   |              |
|                  | f |              |   |       |   |   |              |
|                  | i |              |   |       |   |   |              |
|                  | e |              |   |       |   |   |              |
|                  | d |              |   |       |   |   |              |
+------------------+---+--------------+---+-------+---+---+--------------+

METRIC/ENGLISH CONVERSION FACTORS

<table style="width:100%;">
<colgroup>
<col style="width: 23%" />
<col style="width: 1%" />
<col style="width: 0%" />
<col style="width: 23%" />
<col style="width: 0%" />
<col style="width: 23%" />
<col style="width: 0%" />
<col style="width: 1%" />
<col style="width: 0%" />
<col style="width: 0%" />
<col style="width: 24%" />
</colgroup>
<thead>
<tr class="header">
<th colspan="5"><strong>ENGLISH TO METRIC</strong></th>
<th colspan="6"><strong>METRIC TO ENGLISH</strong></th>
</tr>
<tr class="odd">
<th colspan="5"><strong>LENGTH (APPROXIMATE)</strong></th>
<th colspan="6"><strong>LENGTH (APPROXIMATE)</strong></th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td><strong>1 inch (in)</strong></td>
<td><strong>=</strong></td>
<td colspan="2"><strong>2.5 centimeters (cm)</strong></td>
<td colspan="2"><strong>1 millimeter (mm)</strong></td>
<td colspan="3"><strong>=</strong></td>
<td colspan="2"><strong>0.04 inch (in)</strong></td>
</tr>
<tr class="even">
<td><strong>1 foot (ft)</strong></td>
<td><strong>=</strong></td>
<td colspan="2"><strong>30 centimeters (cm)</strong></td>
<td colspan="2"><strong>1 centimeter (cm)</strong></td>
<td colspan="3"><strong>=</strong></td>
<td colspan="2"><strong>0.4 inch (in)</strong></td>
</tr>
<tr class="odd">
<td><strong>1 yard (yd)</strong></td>
<td><strong>=</strong></td>
<td colspan="2"><strong>0.9 meter (m)</strong></td>
<td colspan="2"><strong>1 meter (m)</strong></td>
<td colspan="3"><strong>=</strong></td>
<td colspan="2"><strong>3.3 feet (ft)</strong></td>
</tr>
<tr class="even">
<td><strong>1 mile (mi)</strong></td>
<td><strong>=</strong></td>
<td colspan="2"><strong>1.6 kilometers (km)</strong></td>
<td colspan="2"><strong>1 meter (m)</strong></td>
<td colspan="3"><strong>=</strong></td>
<td colspan="2"><strong>1.1 yards (yd)</strong></td>
</tr>
<tr class="odd">
<td></td>
<td></td>
<td colspan="2"></td>
<td colspan="2"><strong>1 kilometer (km)</strong></td>
<td colspan="3"><strong>=</strong></td>
<td colspan="2"><strong>0.6 mile (mi)</strong></td>
</tr>
<tr class="even">
<td colspan="5"><strong>AREA (APPROXIMATE)</strong></td>
<td colspan="6"><strong>AREA (APPROXIMATE)</strong></td>
</tr>
<tr class="odd">
<td><strong>1 square inch (sq in, in<sup>2</sup>)</strong></td>
<td><strong>=</strong></td>
<td colspan="2"><strong>6.5 square centimeters
(cm<sup>2</sup>)</strong></td>
<td colspan="2"><strong>1 square centimeter
(cm<sup>2</sup>)</strong></td>
<td colspan="3"><strong>=</strong></td>
<td colspan="2"><strong>0.16 square inch (sq in,
in<sup>2</sup>)</strong></td>
</tr>
<tr class="even">
<td><strong>1 square foot (sq ft, ft<sup>2</sup>)</strong></td>
<td><strong>=</strong></td>
<td colspan="2"><strong>0.09 square meter (m<sup>2</sup>)</strong></td>
<td colspan="2"><strong>1 square meter (m<sup>2</sup>)</strong></td>
<td colspan="3"><strong>=</strong></td>
<td colspan="2"><strong>1.2 square yards (sq yd,
yd<sup>2</sup>)</strong></td>
</tr>
<tr class="odd">
<td><strong>1 square yard (sq yd, yd<sup>2</sup>)</strong></td>
<td><strong>=</strong></td>
<td colspan="2"><strong>0.8 square meter (m<sup>2</sup>)</strong></td>
<td colspan="2"><strong>1 square kilometer
(km<sup>2</sup>)</strong></td>
<td colspan="3"><strong>=</strong></td>
<td colspan="2"><strong>0.4 square mile (sq mi,
mi<sup>2</sup>)</strong></td>
</tr>
<tr class="even">
<td><strong>1 square mile (sq mi, mi<sup>2</sup>)</strong></td>
<td><strong>=</strong></td>
<td colspan="2"><strong>2.6 square kilometers
(km<sup>2</sup>)</strong></td>
<td colspan="2"><strong>10,000 square meters
(m<sup>2</sup>)</strong></td>
<td colspan="3"><strong>=</strong></td>
<td colspan="2"><strong>1 hectare (ha) = 2.5 acres</strong></td>
</tr>
<tr class="odd">
<td><strong>1 acre = 0.4 hectare (he)</strong></td>
<td><strong>=</strong></td>
<td colspan="2"><strong>4,000 square meters
(m<sup>2</sup>)</strong></td>
<td colspan="2"></td>
<td colspan="3"></td>
<td colspan="2"></td>
</tr>
<tr class="even">
<td colspan="5"><strong>MASS - WEIGHT (APPROXIMATE)</strong></td>
<td colspan="6"><strong>MASS - WEIGHT (APPROXIMATE)</strong></td>
</tr>
<tr class="odd">
<td><strong>1 ounce (oz)</strong></td>
<td><strong>=</strong></td>
<td colspan="2"><strong>28 grams (gm)</strong></td>
<td colspan="2"><strong>1 gram (gm)</strong></td>
<td colspan="2"><strong>=</strong></td>
<td colspan="3"><strong>0.036 ounce (oz)</strong></td>
</tr>
<tr class="even">
<td><strong>1 pound (lb)</strong></td>
<td><strong>=</strong></td>
<td colspan="2"><strong>0.45 kilogram (kg)</strong></td>
<td colspan="2"><strong>1 kilogram (kg)</strong></td>
<td colspan="2"><strong>=</strong></td>
<td colspan="3"><strong>2.2 pounds (lb)</strong></td>
</tr>
<tr class="odd">
<td><strong>1 short ton = 2,000 pounds (lb)</strong></td>
<td><strong>=</strong></td>
<td colspan="2"><strong>0.9 tonne (t)</strong></td>
<td colspan="2"><strong>1 tonne (t)</strong></td>
<td colspan="2"><p><strong>=</strong></p>
<p><strong>=</strong></p></td>
<td colspan="3"><p><strong>1,000 kilograms (kg)</strong></p>
<p><strong>1.1 short tons</strong></p></td>
</tr>
<tr class="even">
<td colspan="5"><strong>VOLUME (APPROXIMATE)</strong></td>
<td colspan="6"><strong>VOLUME (APPROXIMATE)</strong></td>
</tr>
<tr class="odd">
<td><strong>1 teaspoon (tsp)</strong></td>
<td colspan="2"><strong>=</strong></td>
<td colspan="2"><strong>5 milliliters (ml)</strong></td>
<td colspan="2"><strong>1 milliliter (ml)</strong></td>
<td colspan="3"><strong>=</strong></td>
<td><strong>0.03 fluid ounce (fl oz)</strong></td>
</tr>
<tr class="even">
<td><strong>1 tablespoon (tbsp)</strong></td>
<td colspan="2"><strong>=</strong></td>
<td colspan="2"><strong>15 milliliters (ml)</strong></td>
<td colspan="2"><strong>1 liter (l)</strong></td>
<td colspan="3"><strong>=</strong></td>
<td><strong>2.1 pints (pt)</strong></td>
</tr>
<tr class="odd">
<td><strong>1 fluid ounce (fl oz)</strong></td>
<td colspan="2"><strong>=</strong></td>
<td colspan="2"><strong>30 milliliters (ml)</strong></td>
<td colspan="2"><strong>1 liter (l)</strong></td>
<td colspan="3"><strong>=</strong></td>
<td><strong>1.06 quarts (qt)</strong></td>
</tr>
<tr class="even">
<td><strong>1 cup (c)</strong></td>
<td colspan="2"><strong>=</strong></td>
<td colspan="2"><strong>0.24 liter (l)</strong></td>
<td colspan="2"><strong>1 liter (l)</strong></td>
<td colspan="3"><strong>=</strong></td>
<td><strong>0.26 gallon (gal)</strong></td>
</tr>
<tr class="odd">
<td><strong>1 pint (pt)</strong></td>
<td colspan="2"><strong>=</strong></td>
<td colspan="2"><strong>0.47 liter (l)</strong></td>
<td colspan="2"></td>
<td colspan="3"></td>
<td></td>
</tr>
<tr class="even">
<td><strong>1 quart (qt)</strong></td>
<td colspan="2"><strong>=</strong></td>
<td colspan="2"><strong>0.96 liter (l)</strong></td>
<td colspan="2"></td>
<td colspan="3"></td>
<td></td>
</tr>
<tr class="odd">
<td><strong>1 gallon (gal)</strong></td>
<td colspan="2"><strong>=</strong></td>
<td colspan="2"><strong>3.8 liters (l)</strong></td>
<td colspan="2"></td>
<td colspan="3"></td>
<td></td>
</tr>
<tr class="even">
<td><strong>1 cubic foot (cu ft, ft<sup>3</sup>)</strong></td>
<td colspan="2"><strong>=</strong></td>
<td colspan="2"><strong>0.03 cubic meter (m<sup>3</sup>)</strong></td>
<td colspan="2"><strong>1 cubic meter (m<sup>3</sup>)</strong></td>
<td colspan="3"><strong>=</strong></td>
<td><strong>36 cubic feet (cu ft, ft<sup>3</sup>)</strong></td>
</tr>
<tr class="odd">
<td><strong>1 cubic yard (cu yd, yd<sup>3</sup>)</strong></td>
<td colspan="2"><strong>=</strong></td>
<td colspan="2"><strong>0.76 cubic meter (m<sup>3</sup>)</strong></td>
<td colspan="2"><strong>1 cubic meter (m<sup>3</sup>)</strong></td>
<td colspan="3"><strong>=</strong></td>
<td><strong>1.3 cubic yards (cu yd, yd<sup>3</sup>)</strong></td>
</tr>
<tr class="even">
<td colspan="5"><strong>TEMPERATURE (EXACT)</strong></td>
<td colspan="6"><strong>TEMPERATURE (EXACT)</strong></td>
</tr>
<tr class="odd">
<td><strong>[(x-32)(5/9)] °F</strong></td>
<td colspan="2"><strong>=</strong></td>
<td colspan="2"><strong>y °C</strong></td>
<td colspan="2"><strong>[(9/5) y + 32] °C</strong></td>
<td colspan="2"><strong>=</strong></td>
<td colspan="2"><strong>x °F</strong></td>
</tr>
</tbody>
</table>

![](media/image4.wmf)

![](media/image5.wmf)

For more exact and or other conversion factors, see NIST Miscellaneous
Publication 286, Units of Weights and Measures. Price \$2.50 SD Catalog
No. C13 10286

# PREFACE {#preface .TOC-1}

Voice radio channels have become increasingly congested as railroad
traffic has increased and railroads centralize their operation centers.
Dispatchers control increasingly large territories and their
communication load has increased as a result. The ability of dispatchers
to communicate effectively with train crews and roadway workers will
impact the safety and productivity of railroad operations.

Digital (data link) communications systems can alleviate the burden of
communication congestion by using a larger bandwidth, capable of
displaying information in visual and auditory forms. The effectiveness
of data link systems to assist dispatchers will depend upon how the
interface is designed and the degree to which the design addresses human
performance limitation and abilities. This report focuses on the safety,
efficiency, and productivity issues associated with the introduction of
a visually based (graphical and textual) data link interface for
railroad dispatchers.

# ACKNOWLEDGMENTS {#acknowledgments .TOC-1}

This research was part of a program initiated by the Federal Railroad
Administration (FRA) to examine the use of digital data link
communications in the railroad environment. This work was performed as
part of an ongoing research program at the John A. Volpe National
Transportation Systems Center, in collaboration with the Human-Machine
System Laboratory at the Massachusetts Institute of Technology (MIT).
The FRA's Office of Research and Development supported this study, as
part of its activities to develop intelligent railroad systems (Federal
Railroad Administration, 2002).

The authors would like to thank Dr. Thomas Raslear of the FRA and Dr.
Donald Sussman of the Volpe Center for their interest and support over
the course of this research.

We also would like to express our deep gratitude to all the people who
helped us during the past 2 years. Dr. Emilie Roth provided insightful
comments on the dispatchers' strategies. Stephen Jones supported our
study by making railroad dispatchers available to participate. John
Pollard provided the expertise to solve many of our technical
challenges. Sarah Miescher, Frank Sheelen, and Drew Kendra showed keen
interest in our study and participated in many discussions. Santanu Basu
provided the essential expertise to build and program the simulator. We
thank Nicolas Oriol for his invaluable comments during earlier drafts of
this study. Finally, we thank all the dispatchers who participated in
our study, for their valued time and energy.

# TABLE OF CONTENTS {#table-of-contents .TOC-1}

**[Section]{.underline} [Page]{.underline}**

[Executive Summary ix](#executive-summary)

[1. Introduction 1](#introduction)

[1.1 The Railroad Environment Today 1](#the-railroad-environment-today)

[1.2 The Existing Environment of the Dispatcher
1](#the-existing-environment-of-the-dispatcher)

[1.2.1 The Dispatcher's Strategies 2](#the-dispatchers-strategies)

[1.2.2 Voice Radio Congestion 3](#voice-radio-congestion)

[1.3 Data Link Communication and the Dispatcher
3](#data-link-communication-and-the-dispatcher)

[1.4 Research Goals 4](#research-goals)

[2. Method 5](#method-1)

[2.1 Overview 5](#overview)

[2.2 Simulator Description 6](#simulator-description)

[2.2.1 The Dispatcher's Interface 6](#the-dispatchers-interface)

[2.2.2 The Experimenter's Interface 7](#the-experimenters-interface)

[2.2.3 Equipment 8](#equipment)

[2.3 Routing Interface 8](#routing-interface)

[2.4 Communication Environments 11](#communication-environments)

[2.4.1 Voice Radio Environment 11](#voice-radio-environment)

[2.4.2 Data Link Environment 11](#data-link-environment)

[2.4.3 Discrete Data Link and Broadcast Data Link
14](#discrete-data-link-and-broadcast-data-link)

[2.5 Scenario Description 15](#scenario-description)

[2.5.1 The Train Schedule 17](#the-train-schedule)

[2.5.2 The Hazard Schedule 17](#the-hazard-schedule)

[2.5.3 The MOW Schedule 17](#the-mow-schedule)

[2.6 Experimental Design 18](#experimental-design)

[2.7 Participants 19](#participants)

[2.8 Procedures 19](#procedures)

[3. Results and Discussion 21](#results-and-discussion)

[3.1 Train Safety 21](#train-safety)

[3.2 Mow Safety 22](#mow-safety)

[3.3 Communication Efficiency 23](#communication-efficiency-1)

[3.3.1 Performance Varies with Message Content
23](#performance-varies-with-message-content)

[3.4 Situation Awareness 28](#situation-awareness)

[3.5 Productivity 29](#productivity)

[3.6 Dispatchers' Preferences 30](#dispatchers-preferences)

[4. Conclusions 33](#conclusions)

[4.1 Future Research 35](#future-research)

[Appendix A. Message Trees 37](#appendix-a.-message-trees)

[Appendix B. Event Schedules 43](#appendix-b.-event-schedules)

[Appendix C. Questionnaires 49](#appendix-c.-questionnaires)

[Appendix D. Experiment Documents 53](#appendix-d.-experiment-documents)

[Glossary 59](#glossary)

[References 61](#references)

# LIST OF FIGURES {#list-of-figures .TOC-1}

[Figure]{.underline} Page

1\. Simulator Configuration [6](#__RefHeading___Toc495302016)

2\. Dispatcher's Workstation [7](#__RefHeading___Toc495302017)

3\. Active Track Layout. [10](#__RefHeading___Toc495302018)

4\. Dispatcher Message Console. [12](#__RefHeading___Toc495302019)

5\. Dispatcher Message Menu Hierarchy [13](#__RefHeading___Toc495302020)

6\. Preprogrammed Message [14](#__RefHeading___Toc495302021)

7\. First Level of Experimenter's Message Tree
[15](#__RefHeading___Toc495302022)

8\. Track Layout [16](#__RefHeading___Toc495302023)

9\. Number of Transactions by Time and Environment
[24](#__RefHeading___Toc495302024)

10\. Distribution of Transactions by Time and Type of Message
[25](#__RefHeading___Toc495302025)

11\. Mean Task Completion Time for Simple and Complex Type Messages by
Communication Environment [26](#__RefHeading___Toc495302026)

# LIST OF TABLES {#list-of-tables .TOC-1}

[Table]{.underline} Page

1\. Meaning of Track Color Coding [8](#__RefHeading___Toc495301876)

2\. Menu Structure of Messages Initiated by Dispatcher
[13](#__RefHeading___Toc495301877)

3\. Territory Elements [15](#__RefHeading___Toc495301878)

4\. Experimental Design [18](#__RefHeading___Toc495301879)

5\. Safety of Trains and MOW Crews by Communication Environment
[21](#__RefHeading___Toc495301880)

6\. Mean Transaction Completion Time by Communication Environment
[23](#__RefHeading___Toc495301881)

7\. Characteristics for Selecting Modality in which to Present
Information [27](#__RefHeading___Toc495301882)

8\. Situation Awareness by Activity and Communication Environment
[28](#__RefHeading___Toc495301883)

9\. Productivity by Communication Environment
[29](#__RefHeading___Toc495301884)

10\. Dispatcher Ratings of Workload, Comfort, and Simulator Realism
[30](#__RefHeading___Toc495301885)

11\. Dispatcher Comments on the Use of Data Link
[31](#__RefHeading___Toc495301886)

#  {#section .Appendix-1 .unnumbered}

## EXECUTIVE SUMMARY {#executive-summary .WW-Contents-2}

The ability of dispatchers to communicate effectively with train crews
and roadway workers impacts the safety and productivity of railroad
operations. Voice radio channels have become increasingly congested as
railroad traffic has increased and operations centers become more
centralized. Data link represents a potential solution to supplement
voice radio. Data link communication differs from voice radio because
the information is digitally coded and discretely addressed. Digital
coding allows many new options in providing communications better
tailored to employee needs.

The additional channel capacity of data link will allow more information
to be communicated. However, the use of data link poses challenges, as
the dispatcher must be able to manage the new communications medium
without experiencing information overload.

The goal of this study was to evaluate how data link affects dispatcher
performance compared to the radio. Two data link environments were
designed and evaluated against the current voice radio environment. The
level of improvement was evaluated in terms of safety, efficiency, and
productivity. Also examined were the dispatcher's attention allocation
strategies.

### Method {#method .WW-Contents-3}

A visual (text-based) data link interface was designed as an alternative
to the current voice radio communication environment. This data link
system was compared to voice radio for common information transmissions
using a railroad dispatcher simulator to evaluate its impact on
dispatcher performance.

The data link interface was modeled after an e-mail application. To send
a message, the dispatcher used a mouse to select from a set of message
templates related to the task being performed. Keyboard entry was needed
only to tailor the message. A data link system was designed with
discrete and broadcast addressing capabilities. The discrete message
capability enabled only private "one to one" communications in which the
dispatcher could send a message to a single recipient. The broadcast
message capability enabled the dispatcher to send a single message to
multiple recipients.

The dispatcher's workstation enabled the dispatcher to route trains and
communicate with workers in the field. The dispatcher used two or three
monitors depending on the communication environment. Two of these
monitors displayed the track layout (routing interface), and one served
as the dispatcher's data link display (communication interface). In the
voice radio environment, a two-way radio was used in place of the data
link display. The dispatcher interacted with the routing (track layout)
monitors using a mouse. For the data link display, a keyboard and mouse
were used. For communication in the data link condition, the dispatcher
used only the data link interface to initiate communication requests or
to reply to people in the field.

Two scenarios were designed using 15 scheduled trains in each. To
evaluate safety, each scenario included two types of hazards:
trespassers on the track and children stoning the train. Each scenario
also included maintenance-of-way (MOW) activities. Using the track
layout screens, the dispatcher routed trains, blocked track, cleared
routes, and took other actions to control equipment in the field.

The following three safety measures were collected: percent of trains
alerted in response to a hazardous event, the percent of MOW crews
properly protected, and situation awareness scores. The questionnaire
was divided into four groups of questions: routing, hazards, MOW
activities, and communications.

To evaluate communication efficiency, total transaction time was
measured. Total transaction time represented the duration of a
transaction between the dispatcher and the respondent. A single
transaction could include multiple exchanges of information.

MOW activity and the "on time" performance of the routed trains were
evaluated. The number of late trains entering the stations were
recorded, as well as the number of trains that were more than five
minutes late. MOW activity was evaluated by recording the number of
granted MOW requests.

The participants were six professional dispatchers: one woman and five
men. Three participants had 7 to 9 years dispatching experience, while
the other three had less than 2 years. Participants were paid the same
hourly rate they received for performing their usual job duties.

Each dispatcher participated in two scenarios, with a different
communication environment each time. Before each trial, dispatchers were
trained on the interface they would use. After the experiment, there was
a short debriefing session. Each trial lasted one hour, and was
interrupted once after 30 minutes so the participant could complete a
situation awareness questionnaire. The participant's task was to perform
their usual dispatching task given the constraints imposed by the new
environments. At the conclusion of each scenario, the dispatcher
completed a brief questionnaire.

### Data Link Improves Communication {#data-link-improves-communication .WW-Contents-3}

Our results suggest that data link can improve communication efficiency,
safety, and situation awareness. The differences between conditions were
not always statistically significant, but in almost every case, they
favored data link. Compared to voice radio, both data link systems
improved safety and situation awareness. For productivity, no
differences were observed between data link conditions and voice radio.

With data link, dispatchers protected a greater percentage of trains and
MOW crews as compared to the radio. By providing information in a visual
format, data link eliminated readback errors and hearback errors
associated with the auditory modality. Translating track requests from
alphanumeric text to a graphic display on the track layout display made
the request even easier to process. The visual presentation of
information in the data link systems minimized the demand placed on the
dispatcher's memory. Anecdotal comments by the participants suggested it
also reduced stress by giving the dispatcher the opportunity to respond
to messages when time allowed, providing a quieter environment in which
to work.

The advantage of communicating information in visual form was evident in
the evaluation of situation awareness. Situation awareness for data link
was better than voice radio for routing, hazard awareness, and
communication. While the dispatcher devoted more resources to processing
visual information with data link than with radio (there were three
displays to monitor, instead of two), no adverse impact was evident. MOW
activity was the only category in which performance was as good or
better than the radio condition. Dispatchers had a visual form of
information to assist them in situation awareness.

Overall, the differences between the discrete data link condition and
the broadcast data link condition were small. The broadcast version
showed a greater improvement in train safety than the discrete version.
The broadcast version minimized communication workload by providing a
simple way to reach multiple recipients, allowing the dispatcher to
attend to other tasks. For example, the dispatcher could use a single
message to alert all trains along a particular branch, while the
discrete system required the dispatcher to contact each train
individually.

Communication efficiency for voice radio and data link varied as a
function of the characteristics of each medium. Information communicated
by voice radio was presented in an auditory format. Information
communicated via data link was presented in a visual format. Each form
proved better suited for presenting some kinds of information than
others.

Voice radio proved better suited to communicating short and informal
communications as well as time-critical messages that required immediate
action (i.e., a dispatcher reporting no speed restrictions when a
locomotive engineer called to request a temporary speed-restriction
bulletin, or alerting a locomotive engineer to the presence of a
trespasser). For these types of communications, data link doubled the
communication times over voice radio. These results were due to the
auditory format in which the information was presented.

In this experiment, data link was better suited for communications whose
length or complexity imposed a significant burden on memory. In railroad
operations, these characteristics are typical of safety critical
messages that require formal acknowledgement procedures (i.e., granting
a Foul Time request or authorizing a train movement using a Form D).
Data link provided an efficient channel for these communications. As a
result, communication times were reduced by a factor of two. The concept
of not having to repeat a message multiple times was also appealing to
the dispatchers in our study.

In the voice radio and data link conditions, the performance differences
observed between the two types of messages were due to the modality or
format in which the information was presented, not the communication
medium. While information sent over voice radio is presented in an
auditory form, digital communications systems like data link provide
more options for presentation. Data link supports both auditory and
visual modalities.

The differences identified between radio and data link also depended
upon the details of how each interface was implemented. Had the data
link interface required the dispatcher to make heavier use of the
keyboard to enter messages than with the current design, the results
might have been quite different. Successful implementation of a data
link interface will depend upon applying principles of good human
factors design and usability testing to meet the needs of dispatchers
who use this communication interface.

The current study suggests that dispatchers benefit from both voice and
data link communication modes. In recommending the conditions under
which each medium should be used, this study suggests that voice radio
is best suited for communicating simple, time-sensitive messages to one
recipient. Data link system is best suited for communicating lengthy
messages. Sending discrete messages works best where privacy is
important or the message content would benefit only the recipient for
which the message is intended. Sending broadcast messages works best
when there is a need to communicate the same information to multiple
recipients.

#  {#section-1 .unnumbered}

# INTRODUCTION

## The Railroad Environment Today

Railroad traffic has increased in recent years. As a result, railroads
have improved their infrastructure by investing in faster trains and new
technologies to enhance train movements. Between 1992 and 1995,
railroads bought more than 800 new locomotives (Railroad Facts, 1996).
The Federal Railroad Administration (FRA) and the railroad industry are
working together on the development of intelligent railroad systems that
include new computer and communications technologies in train control
and the scheduling of railroad operations (FRA, 2002).

One consequence of these changes is the movement toward more efficient
communication. Dispatchers must work closely with train crews and
roadway workers to manage track use. Managing the communication process
is a challenge, given the current voice radio channel availability.
Using voice radio as the primary communication channel in the railroad
environment has resulted in communication congestion. Data link
communication can provide capabilities not available through voice
radio. However, the use of data link itself poses challenges, as the
dispatcher must be able to manage the additional communications.

Currently, the dispatcher acquires information from parties in the field
by way of voice radio and telephone. By what criteria will a dispatcher
select the communication medium, when data link becomes available for
sending and receiving information? What kind of information is
appropriate for each medium? To address these questions it is important
to first understand how the dispatcher acquires and shares information
in the current environment. To begin answering these questions, the
current communication environment of the dispatcher was analyzed.

## The Existing Environment of the Dispatcher

Railroad dispatchers are responsible for managing track use, ensuring
that trains are routed safely and efficiently, and ensuring the safety
of the maintenance-of-way (MOW) personnel working on and around the
track (Devoe, 1974). These tasks require integrating multiple sources of
information, projecting track use into the future, and balancing
multiple demands from various sources. The railroad dispatcher is
responsible for the safety of people and equipment on the track as well
as the efficient use of railroad resources. By contrast, in the aviation
environment, these two job functions are divided between the air traffic
controller whose primary concern is safety and the airline dispatcher
whose primary concern is productivity.

Successful performance of the train routing task depends on the ability
of the dispatchers to monitor train movements beyond their territory,
balance multiple demands placed on track use, and factor in unplanned
events in allocating track. This requires monitoring train positions and
MOW activities. In CTC territories, the dispatcher monitors train
position via signals communicated by track circuitry, on a visual
display (i.e., a computer display or mimic board) and monitors events
through two-way radio communications with railroad crews in the field.
In territories, where information about train position is not available
(either Automatic Block Signal territory or dark territory), the
dispatcher must rely upon voice radio communications with railroad
personnel in the field as the only means to monitor train movements.

Voice radio traffic places significant demands on the dispatcher's
attention and memory. To stay informed and in control the dispatcher
performs a variety of tasks. These tasks include: answering requests,
determining the current state of railroad operations (delays, speed
restrictions, and track outages), informing railroad entities of the
current state of operations, coordinating with other railroad
"supervisors" (e.g., train masters and yard masters), and filling out
paperwork.

These tasks contribute to three types of demands on the dispatcher:

-   Demands on attention associated with monitoring the radio channel
    and responding to radio requests.

-   Demands on memory, associated with the need to keep track of many
    more elements than the ones actually displayed on the routing or
    communication interface.

-   Demands on decision-making strategies associated with the assignment
    of track to trains or MOW crews.

### The Dispatcher's Strategies

Dispatchers have developed several strategies for meeting their job
demands (Roth, Malsch and Multer, 1999). Awareness of dispatcher
strategies is important for designers considering new aiding
technologies. Strategies can signal problems in the current dispatching
environment that dispatchers are compensating for, and may suggest ideas
for new aids. When introducing new technologies, designers need to be
careful not to inadvertently create conditions that prevent the
dispatchers from implementing their strategies, especially if there is
no replacement strategy.

One strategy consists of off-loading memory requirements. A great amount
of information needs to be considered when making track allocation or
routing decisions. Some of this information can be found in rulebooks,
schedules, memos, and daily bulletins. Dispatchers have developed
techniques to extract key pieces of information in a more accessible
form. One example is the "cheat sheet," which is a piece of paper
summarizing the most relevant information in the schedule. Another
example is the desk book, a clipboard including formal memos, speed
bulletins, scheduled track outages, or informal notes written by the
dispatcher. Both tools provide the dispatcher with a convenient way of
keeping track of changes and updates.

A second set of strategies is to anticipate unplanned events and plan
ways to address these events. These strategies include coordination with
the dispatchers for abutting territories and from the people in the
field (i.e., asking adjoining dispatchers about changes in the usual
routing and alerting them to changes caused by unplanned events). The
dispatcher develops a "game plan" to work out meets and passes depending
on train schedules and priorities for each shift and territory ahead of
time. Dispatchers may summarize parts of the game plan in their cheat
sheets. To maintain the "big picture" they monitor activity beyond their
territory. If an overview display showing track use for all territories
is available, they monitor where trains are on the track even before
they enter their territory. Dispatchers also take advantage of the party
line feature of the voice radio. Dispatchers listen for information on
the radio channel not directly addressed to them. This information can
provide important clues to potential delays or problems. Typically,
dispatchers listen for "train out of station" messages, equipment
problems, (when a locomotive engineer is talking to the mechanical
department), and other dispatcher commitments that might have an impact
on their territories.

Dispatchers plan by developing contingencies for unplanned events such
as engine failures and late or unscheduled trains. Planning includes
taking advantage of the windows of opportunity for track usage. If track
that was previously in use becomes available earlier than expected,
dispatchers will call up a MOW crew to let them know it is available. In
the same manner, they will call locomotive engineers before a train is
scheduled to leave the station to give them the speed bulletin for the
trip.

A third strategy is to level workload. Dispatchers try to shift the work
from high workload periods to lower workload periods. For example
dispatchers will pre-name trains, clear routes in anticipation of needs,
and give provisional authority (giving track away until further notice).
Other methods include reducing the amount of communication (especially
for work crews), and performing multiple tasks in parallel (e.g.,
clearing a route for a train and answering the radio for a MOW person).

### Voice Radio Congestion

There was consensus among the interviewed dispatchers that the voice
radio channel is often overloaded. Furthermore, there was agreement that
voice radio is not well suited for some communication tasks. For
example, long dialogues intended to convey detailed information such as
exact location, should be conducted on a more private voice channel
(i.e., telephone).

## Data Link Communication and the Dispatcher

Data link technology provides an alternative that can supplement voice
radio and telephone communications. Data link communication differs from
voice radio because the information is digitally coded. This makes it
possible to discretely address individual receivers or multiple
recipients.

Data link would benefit the railroad industry by making data available
in real time, while improving information in terms of quantity,
reliability, and quality (Vanderhorst, 1990). Real time transmission of
information could improve the dispatcher decision-making process. The
contribution of real time information can be understood when one
observes the current dispatching environment. For example, at one
dispatching center, with passenger trains comprising the majority of
traffic, the system shows delays for each train. However, the
information is not displayed in real time. As a result, the dispatchers
cannot rely on this information for time-critical decisions. They need
to solicit additional sources of information and use strategies for
allocating track that depends upon a coarser level of information.
Current data link technologies could help.

Additional channel capacity of data link means that more information can
be communicated. However, increasing the amount of data could lead to
information overload. To use the new technology efficiently, data link
must provide additional data that can be turned into useful information.
Information normally provided aurally could be displayed visually. This
feature would assist dispatchers in managing their workload.

Data link also has the potential to address the voice radio congestion
problem. Data link will reduce congestion in the radio environment by
providing an alternative, higher bandwidth communication channel.
Currently, only one person can transmit over a given voice radio
channel. When someone transmits a message, other parties are blocked
from transmitting their messages over the same channel. Data link
enables many people to transmit multiple messages simultaneously. Data
link may also change the order in which messages are answered.
Currently, the order in which messages are answered depends upon the
dispatcher's implicit, situationally dependent priority. The ability to
store and display messages will require that messages are organized to
facilitate the dispatcher's tasks. This organization can make explicit
(observable) the dispatcher's priorities. Thus, data link changes the
nature of the communication problem for the dispatcher. Instead of
answering messages in the order they arrive, now the dispatcher or the
system must prioritize the order in which messages are answered. In the
current radio environment, the dispatcher faces a similar situation
because there are several frequencies over which people can communicate.
Data link highlights this challenge for the dispatcher. Designers will
need to consider ways to help the dispatcher prioritize the order in
which messages are answered.

Data link also provides the ability to design flexible interfaces
(either visual or aural) for delivering information. However, the
success of this communication channel is likely to depend upon its
implementation. Simply adding data link technology without considering
how information will be presented may create new problems. Advantages
present in the current voice radio environment can be lost if designers
do not understand their importance.

Using data link, information can be presented aurally or visually. Each
modality has advantages and disadvantages. What information should be
sent via data link and what information should be communicated by voice?
This study seeks to answer this question by examining how data link
affects railroad dispatcher performance. As the focal point for
communications in the railroad control environment, the benefits and
drawbacks of implementing data link in the dispatcher's working
environment were investigated.

## Research Goals

The goal of this study was to evaluate how data link affected dispatcher
performance compared to the current voice radio channel. Using a
railroad dispatcher simulator, two data link environments were designed
and evaluated against the current voice radio system. The level of
improvement in terms of safety, efficiency, and productivity within this
new environment was evaluated. The dispatcher's attention allocation
strategies were also examined.

# METHOD

## Overview

The performance differences between data link and voice radio were
measured using a human-in-the-loop railroad dispatcher simulator. In the
voice condition, messages were communicated by two-way radio.
Transactions communicated by radio were synchronous; the transaction
between sender and receiver took place at the same point in time. Use of
a voice radio channel by a sender blocked its use by other potential
senders. Therefore, a message could only be sent by one person at time.
However, anyone in range of the communication could listen to the
message.

A user interface for a data link system was created to operate similarly
to an email system. The dispatcher interacted with the data link system
using a computer monitor, keyboard, and mouse. Unlike voice radio, the
data link system was asynchronous. Transactions communicated by radio
were asynchronous; transactions between senders and receivers could take
place at different points in time. The sender of a message could send a
message to one recipient or to many recipients.

Although a real-world system would have both capabilities, in the
current study, these two ways of sending messages were separated into
two experimental data link conditions to evaluate their impact on
dispatcher performance. The two data link conditions were called
discrete and broadcast. In the discrete condition, messages were sent to
a single recipient. In the broadcast condition, messages were sent to
multiple designated recipients. Each type of message distribution has
advantages and disadvantages. Sending a single message to multiple
recipients in one transaction by the dispatcher requires less work than
sending the same message multiple times. The challenge is determining
who received the message. For safety critical transactions, the
dispatcher needs confirmation that the recipient received the message.
Sending messages to recipients who don't need this information may
overload the recipients with unnecessary information. Conversely,
failing to send it to a recipient who should have received this
information could contribute to a mishap.

In the two data link conditions, voice radio was not used. The two
communication environments were evaluated separately to identify the
effects of each communication environment on dispatcher performance.

Dispatchers performed their normal duties routing trains and allocating
track to maintenance of way (MOW) crews. Each participant was exposed to
two scenarios in which a variety of events occurred such as trespassers
on the tracks, delayed trains, and requests from track personnel for
Foul Time. Participant performance was measured in terms of efficiency
(minimizing communication time), productivity (minimizing train delays
and maximizing maintenance work), safety (avoiding collisions), and
attention allocation.

![](media/image6.png){width="5.997916666666667in"
height="3.9743055555555555in"}

[]{#__RefHeading___Toc495302016 .anchor}Figure 1. Simulator
Configuration

## Simulator Description

The simulator was divided into two parts as shown in Figure 1: the
dispatcher's workstation and the experimenter's workstation. Each
workstation was composed of two display elements, reflecting the two
main activities of the dispatcher: routing and communication. The
routing interface displayed the track layout and was modeled after a
Central Traffic Control (CTC) based signal system. It simulated routing
activity for a track network on the Northeast Corridor. The
communication interface was either a portable two-way radio or a data
link display, depending on the experimental condition.

### The Dispatcher's Interface

The dispatcher's workstation enabled the dispatcher to route trains and
communicate with workers in the field. The dispatcher used two or three
monitors depending on the communication environment. Two of these
monitors displayed the track layout (routing interface) and one served
as the dispatcher's data link display (communication interface) as seen
in Figure 2. In the voice radio environment, a two-way radio was used in
place of the data link display. The dispatcher interacted with the
routing (track layout) monitors using a mouse. For the data link
display, a keyboard and mouse were used.

![](media/image7.png){width="5.572222222222222in"
height="3.532638888888889in"}

[]{#__RefHeading___Toc495302017 .anchor}Figure 2. Dispatcher's
Workstation

Using the track layout screens, the dispatcher routed trains, blocked
track, cleared routes, and took other actions to control equipment in
the field. For communication in both data link environments, the
dispatcher used the data link interface to initiate communication
requests or to reply to people in the field.

### The Experimenter's Interface

The experimenter's workstation enabled the experimenter to monitor the
experiment and to play the roles of other entities with whom the
dispatcher would interact. These entities included: train crews, MOW
crews, yardmasters, trespassers, and other dispatchers. For example, the
experimenter could halt, reverse direction, or derail a train. Although
the experimenter's workstation consisted of the same three monitors as
the dispatcher's workstation (as shown in Figure 2), the experimenter's
workstation did not allow dispatching activities. The experimenter
controlled the routing interface and data link interface with the
appropriate keyboard and mouse.

Two monitors displayed the track layout. The third monitor displayed the
data link interface. In the radio environment, the experimenter used
three portable radios in place of the data link display. Playing the
role of other railroad staff involved the use of assistants
communicating with each other and the dispatcher about events taking
place.

In the data link environment, the experimenter used the message console
to communicate with the dispatcher. Preprogrammed messages were created
to play the part of other railroad operating personnel. However, the
type of preprogrammed messages differed from those available to the
dispatcher. In the voice radio environment, the experimenter(s) still
used the message console because it provided the appropriate message to
read aloud on the radio. For more details about the operation of the
simulator, see Basu (1999).

### Equipment

The railroad dispatcher simulator was comprised of six personal
computers (PCs) connected via a local area network (LAN), and a set of
four portable radios. Each was a Windows™ based machine with a Pentium™
II class processor. Seventeen-inch cathode ray tube (CRT) type monitors
were used. The simulation was programmed using Java™.

The dispatcher's workstation consisted of three PCs. The experimenter's
workstation was located in an adjacent room, and consisted of three PCs.
The three PCs in the dispatcher's room were connected via a LAN to the
three PCs in the experimenter's room. The experimenter initiated actions
or created conditions to which the dispatcher responded. Alternatively,
the experimenter, playing the role of locomotive engineer, roadway
worker, or another dispatcher, responded to events or action initiated
by the dispatcher.

Four Motorola HT/MT1000 portable radios were used to simulate voice
radio communication. One radio was present in the dispatcher's room, and
the experimenter and two assistants used the remaining three radios. In
the voice radio condition, three people simulated the communications of
the operating personnel amongst themselves and with the dispatcher. A
video camera located in the participants' room recorded all experimental
trials.

## Routing Interface

The routing simulation was modeled on an Amtrak passenger railroad
dispatching system. It showed a color-coded track display with text to
display the current track state.

**Color-coding** *-* The color of individual track segments (referred to
as blocks) represented how the track was allocated. The color-coding
conformed to the conventions as seen in Table 1.

  --------------------------------- ----------------------------------------------------------
  []{#__RefHeading___Toc495301876   
  .anchor}Table 1. Meaning of Track 
  Color Coding                      

  **Color**                         **Meaning**

  Red                               Indicates the presence of a train. Other trains are not
                                    allowed in this block.

  Green                             Cleared route. Train has permission to enter this block.

  Blue                              Indicates track work is occurring. Trains are not allowed
                                    to enter without permission of MOW workers.

  White                             Track is currently unallocated.
  --------------------------------- ----------------------------------------------------------

**Text information** *-* Train numbers were displayed above the track if
traveling outbound and below the track if traveling inbound. Inbound
trains had even numbers and outbound trains had odd numbers. In
addition, an arrow was located on the left or on the right of the train
number to indicate travel direction. Finally, a plus or minus sign was
displayed on the left of the train number to indicate whether the train
was ahead of or behind schedule. This display was only updated when a
train passed an interlocking. Stations and interlockings were named.

**Track layout** *-* The track consisted of a terminal station named
Boston, with ten platforms from which four branches departed towards New
York City as shown in Figure 3. The four branches, labeled A, B, C, and
D respectively, varied in length and number of stations.

**Routing activities** *-* The main routing tasks were accomplished
using mouse-activated buttons located at the bottom of the screen;
clearing and unclearing a route as well as blocking and unblocking
tracks. Clearing a route enabled a train to move over that section of
track. Other trains were prohibited by the signal system from entering
track sections occupied by the train. Unclearing a route made the
previously cleared track available for other uses. The track uncleared
automatically after the train went through. The unclearing delay
typically encountered by dispatchers when correcting a mistake was not
implemented. If a switch was changed while the train was in an
interlocking, the change did not affect the train's movement. A
two-aspect signal system (clear route or route occupied) was
implemented. The dispatcher blocked a track to enable roadway workers
and their equipment to occupy the track. Unblocking the track removed
this protection for the roadway worker crew and equipment and made the
track available for train movements or other MOW crews. The simulator
propagated the state of the signal to the adjacent block. Hence, trains
slowed down and eventually stopped if a cleared route was not available.

![](media/image8.wmf)

[]{#__RefHeading___Toc495302018 .anchor}Figure 3. Active Track Layout

## Communication Environments

### Voice Radio Environment

The experimental communication procedures were modeled after a
communication protocol used at a scheduled train operations dispatching
center. Messages transmitted to the dispatcher were computer generated
in accordance with the dispatcher's routing decision. If the simulator
was programmed to act on the presence of a trespasser within a given
time span, and the dispatcher was routing a train through the area where
the trespasser was, the simulator would then send a message to the
experimenter. The experimenter, playing the role of the locomotive
engineer on that particular train, then called the dispatcher on the
radio to warn of the trespasser's presence. If the dispatcher routed no
trains through the territory while trespassers were supposedly present
there, these trespassers went unnoticed by the dispatcher.

Communications were not always directed to the dispatcher. To simulate
communications among field personnel, the experimenter and several
assistants used a set of computer-generated cues to talk amongst
themselves using the three radios. The experimenters used the same
communication protocol as the dispatcher.

### Data Link Environment

The data link environment was displayed visually using an e-mail-like
interface. The data link interface contained a menu of preprogrammed
messages. The voice radio was unavailable in the data link conditions.
The data link interface consisted of a monitor with a mouse and keyboard
for information input. To send a message, the dispatcher used a mouse to
select from a set of message templates (containing text) relating to the
task being performed. Keyboard entry was needed only to tailor the
message. This approach minimized the need for time-consuming keyboard
use. Two ways of sending messages using the data link system were
designed: discrete and broadcast. The discrete message capability
enabled only private "one to one" communications in which the dispatcher
could send a message to a single recipient. The broadcast message
capability enabled one to many communications in which the dispatcher
could send a message to multiple recipients. The screen was split into
four windows as shown in Figure 4.

**Received messages window** *-* The upper left window of Figure 4
displays the list of received messages. With each incoming message, an
additional line was added to the list specifying the sender. Messages
were sorted by arrival time. If unselected, messages were preceded by a
series of four question marks. Once highlighted, messages were preceded
by a series of stars. If the dispatcher used the reply button to answer
a message, the message was preceded by a series of "Rs."

**Text message window for received messages** *-* The lower left window
of Figure 4 displays the entire text of the selected message. If this
message referred to a track location, this location was highlighted in
yellow on the track layout display.

![](media/image9.wmf)

[]{#__RefHeading___Toc495302019 .anchor}Figure 4. Dispatcher Message
Console

**Sent message window** *-* The upper right window in Figure 4 displays
the list of outgoing messages. With each sent message, another line was
added to the list. Each line contained the recipient and the subject of
the message.

**Text message window for sent messages** *-* The lower right window
shown in Figure 4, displays the entire text of the message the
dispatcher highlighted in the sent message window. This text window
lacked the track location-highlighting feature.

**Message creation: the dispatcher's message-tree** - To facilitate
message creation, the most frequently used message types were
preprogrammed. The dispatcher scrolled within a hierarchical menu to
select a message. The menu contained a small number of fundamental
messages. Clicking the reply button or the send message button at the
bottom of the received-messages window displayed a menu. The menu
consisted of a four level tree, through which the sender proceeded in
sequence, from level one to level four. The menu hierarchy is shown in
Table 2 and Figure 5.

+-------+--------------------------+-----------------------------------+
| [     |                          |                                   |
| ]{#__ |                          |                                   |
| RefHe |                          |                                   |
| ading |                          |                                   |
| ___To |                          |                                   |
| c4953 |                          |                                   |
| 01877 |                          |                                   |
| .an   |                          |                                   |
| chor} |                          |                                   |
| Table |                          |                                   |
| 2.    |                          |                                   |
| Menu  |                          |                                   |
| Stru  |                          |                                   |
| cture |                          |                                   |
| of    |                          |                                   |
| Mes   |                          |                                   |
| sages |                          |                                   |
| Init  |                          |                                   |
| iated |                          |                                   |
| by    |                          |                                   |
| Dispa |                          |                                   |
| tcher |                          |                                   |
+-------+--------------------------+-----------------------------------+
| **Le  | **Content**              | **Example**                       |
| vel** |                          |                                   |
+-------+--------------------------+-----------------------------------+
| 1     | Message Priority         | High, medium or low               |
+-------+--------------------------+-----------------------------------+
| 2     | Recipient                | Engineer, MOW                     |
+-------+--------------------------+-----------------------------------+
| 3     | General subject          | Trespasser, Kids throwing stones  |
+-------+--------------------------+-----------------------------------+
| 4     | Detailed message content | Track Work -- Foul Time Granted   |
|       |                          |                                   |
|       |                          | Track Work -- Foul Time Refused   |
+-------+--------------------------+-----------------------------------+

Clicking a button in the fourth level of the message tree hierarchy
displayed a window with the desired message. If the dispatcher wanted to
send a message not found in the message tree, a "blank message" could be
created.

+-----------------------------------+-----------------------------------+
| ![](med                           | ![](media/image11.                |
| ia/image10.png){width="2.06875in" | png){width="1.5409722222222222in" |
| height="3.9541666666666666in"}    | height="1.1993055555555556in"}    |
|                                   |                                   |
| First two levels of message tree  |                                   |
+-----------------------------------+-----------------------------------+
|                                   | Third level of message tree       |
+-----------------------------------+-----------------------------------+
|                                   | ![](media/image12.                |
|                                   | png){width="2.3194444444444446in" |
|                                   | height="1.695138888888889in"}     |
+-----------------------------------+-----------------------------------+
|                                   | Fourth level of message tree      |
+-----------------------------------+-----------------------------------+
| []{#__RefHeading___Toc495302020   |                                   |
| .anchor}Figure 5. Dispatcher      |                                   |
| Message Menu Hierarchy            |                                   |
+-----------------------------------+-----------------------------------+

The entire dispatcher message tree used in the data link environments is
shown in Appendix A. To complete a message, the dispatcher filled in the
blanks using the mouse or keyboard (see Figure 6). Typically, the
dispatcher filled in a location, time, and train number. To specify
location or train number, the dispatcher used the mouse. By selecting
the location or train number on the track layout display, the blank
fields in the message were completed automatically. Once a field was
filled in, the cursor moved to the next blank field. In the final step,
the dispatcher pressed the send button to deliver the message. Once
sent, messages were always acknowledged.

![](media/image13.png){width="4.004166666666666in"
height="3.8493055555555555in"}

[]{#__RefHeading___Toc495302021 .anchor}Figure 6. Preprogrammed Message

### Discrete Data Link and Broadcast Data Link

With the discrete data link condition, messages were sent to only
[one]{.underline} recipient. In the broadcast data link condition,
messages were always sent to [multiple]{.underline} recipients. To send
a message, the dispatcher specified one primary recipient and a group of
secondary recipients (see Appendix A for the list of the groups). It was
assumed that recipients always properly acknowledged messages.

The experimenter's data link interface was identical to the dispatcher's
message console. To create a message, the experimenter used the same
procedure as the dispatcher. However, the experimenter had message trees
available for all railroad entities such as a dispatcher tree, an
engineer tree, a MOW tree, and a "miscellaneous" tree as shown in Figure
7. The message trees were similar in structure to the previously
described dispatcher message tree. The experimenter message tree can be
found in Appendix A.

![](media/image14.png){width="1.3604166666666666in" height="2.275in"}

[]{#__RefHeading___Toc495302022 .anchor}Figure 7. First Level of
Experimenter's Message Tree

## Scenario Description

Two scenarios were designed. Each experimental run started at the
beginning of a new shift and lasted one hour. Figure 8 represents the
territory for which the dispatcher was responsible. The territory for
both scenarios was the same. The territory contained the elements shown
in Table 3. The top track layout shows the terminal on the left. The
track at the right side of the top track layout is located south of the
track to the left. On the bottom display, the left side of the track
layout continues the display shown on the right hand side of the top
track layout.[^1]

  -----------------------------------------------------------------------
  []{#__RefHeading___Toc495301878 .anchor}Table 3. Territory Elements

  **Territory Elements**

  Four branches: A, B, C, D

  One Terminal station

  Four intermediate stations: A, BL, BR, D

  One drawbridge (not displayed, between D7 and D8)
  -----------------------------------------------------------------------

![](media/image15.png){width="5.997222222222222in"
height="3.9034722222222222in"}

![](media/image16.png){width="5.99375in" height="4.007638888888889in"}

[]{#__RefHeading___Toc495302023 .anchor}Figure 8. Track Layout

### The Train Schedule

Fifteen scheduled trains were used during each scenario. The schedule
and the territory were designed so that if the dispatcher routed the
trains perfectly, all trains could arrive on time or slightly early. If
the dispatcher made a significant routing mistake (i.e., forgetting
about a train for five minutes or longer), the affected train could not
make up for the delay. Small routing mistakes (one or two minutes) did
not appear in the data. This was done to simulate the fact that
engineers will try to make up for their delays. During the experiment,
dispatchers had a copy of the schedule readily available.

Trains outside of the stations were moving when the simulation began.
All trains were on time and had sufficient track to move at full speed
for the first three minutes of the simulation without any action by the
dispatcher. The entire train schedule is shown in Appendix B.

### The Hazard Schedule

To evaluate safety, two types of hazards were used; each scenario
included five hazards. The first type of hazard was the presence of
trespassers on the track. Two or three times during each experiment,
trespassers were present on the track for a certain period. If during
that period of time a train passed through the area, the locomotive
engineer saw the trespassers and the dispatcher was alerted. The
dispatcher was expected to relay the trespasser alert to all other
trains that would travel through that area. The second type of hazard
was children stoning the train, which occurred twice during each
experiment. If trains were routed into the hazardous area at the "right"
time, the dispatcher was alerted and had to relay the information to the
other trains near the hazard.

To collect enough data, these two types of hazards were scheduled to
take place in an area with heavy train traffic. The appropriate hazard
occurrence time was chosen so that delays between five and ten minutes
would not prevent the experimenter from gathering enough data. The
territory was busy enough and the hazard schedule designed to account
for variations in routing. For details on the hazard presence times and
on the expected "alerter trains," see Appendix B.

### The MOW Schedule

Each scenario included MOW activities. To provide enough data points to
compare performance between conditions and to create a moderately
stressful workload, the number of MOW requests a dispatcher would
normally face was exaggerated. After preliminary testing, 12 track
requests were made during each scenario. These 12 requests included:

-   2 bridge lifting requests

-   2 management-scheduled track outages

-   8 unscheduled MOW requests

At the beginning of each experiment, the dispatcher took over the
protection of two MOW crews who were granted permission by the previous
dispatcher on the shift.

There were two types of unscheduled MOW activity. The first activity was
signal work. Signal workers requested protection for work on the signals
near an interlocking. The second type of activity was track work. Track
work was requested and performed either by track cars (special trucks
riding on the track and checking its condition) or by repair crews. In
the data link case, there were two different answer messages, one for
each type of MOW crew. Dispatchers were expected to use the appropriate
reply message, depending on the type of request. In the radio condition,
dispatchers were instructed to use the "Form D" movement authority for
all MOW requests.

The MOW schedule was designed to create challenging "meets and passes"
problems for the dispatcher. At least one MOW request could not be
granted if all trains were on time. Appendix B shows the MOW schedule.

## Experimental Design

The type of communication environment was the independent variable.
There were three levels: radio, discrete data link (DD), and broadcast
data link (BD). The experimental design is shown in Table 4. A balanced
incomplete block design (Lindman, 1992) was used. All dispatchers
started with a data link scenario.

  --------------------------------- ----------------- --------------- ---------------
  []{#__RefHeading___Toc495301879                                     
  .anchor}Table 4. Experimental                                       
  Design                                                              

  **Dispatcher**                    **Environment**                   

                                    **Radio**         **Data link**   

                                                      **Discrete**    **Broadcast**

  1                                 Scenario 1        Scenario 2      

  2                                 Scenario 2        Scenario 1      

  3                                 Scenario 1                        Scenario 2

  4                                 Scenario 2                        Scenario 1

  5                                                   Scenario 1      Scenario 2

  6                                                   Scenario 2      Scenario 1
  --------------------------------- ----------------- --------------- ---------------

The dependent variables (i.e., measured variables) can be classified
into three groups:

-   Safety

-   Efficiency measurements of the communication system

-   Productivity

#### Safety Measures

Three safety measures were collected. Two measures related to action
taken by the dispatcher to warn or protect trains and MOW crews. The
third safety measure concerned situation awareness. The two safety
measures related to warning or protecting trains and MOW crews were: the
percent of trains alerted in response to a hazardous event, and the
percent of MOW crews properly protected.

In the first safety measure for each hazard, a fixed number of trains
were supposed to receive a warning message. For each train properly
warned, the dispatcher earned one point.[^2] All scores were converted
into percentages.

The second safety measure was the number of MOW crews protected properly
when Foul Time or Form D movement authority was granted. For each MOW
request granted, the pieces of track asked for and the pieces of track
given away were recorded. When MOW people were protected, the dispatcher
earned one point. The number of points varied with each dispatcher. The
percentage of MOW crews protected was calculated by dividing the number
of properly protected MOW crews by the number of MOW requests granted
for each dispatcher.

The third safety measure was situation awareness, which was evaluated
using the Situation Awareness Global Assessment Technique (SAGAT)
developed by Endsley (1993). During the experiment, the simulation was
paused so that the participant could complete a questionnaire. The
questionnaire was divided into four groups of questions: routing,
hazards, MOW activities, and communications questions. A dispatcher
received one point for each correct answer. Partial credit was given if
the answer was partially correct. For details about the questionnaire,
see Appendix C.

#### Communication Efficiency

To evaluate communication efficiency, total transaction time was
measured. Total transaction time represented the duration of a
transaction between the dispatcher and the respondent. A single
transaction could include multiple exchanges of information. The
duration was measured from the time at which an initial message was
received by the dispatcher to the time at which final response was sent
by the dispatcher.

In the radio environment in this experiment, the initiation of the
message and reception occurred simultaneously. In the data link
environment, a delay could occur between the time the message was
displayed on the monitor and the time the dispatcher observed and read
the message. In the data link condition, the time at which the message
was displayed on the monitor represented the initiating event for
measuring total transaction time. The transaction was considered
complete in the radio environment when the dispatcher completed the
verbal response. In the data link condition, the transaction was
completed after the message was sent and the experimenter forwarded the
message to the appropriate recipient.

#### Productivity Operations

MOW activity and the "on time" performance of the trains were evaluated.
The number of trains entering a station was known for all dispatchers.
The number of late trains entering the stations were recorded, as well
as the number of trains that were more than five minutes late. MOW
activity was evaluated by recording the number of granted MOW requests.

## Participants

The participants were six professional Amtrak dispatchers: one woman and
five men. Three participants had 7 to 9 years dispatching experience.
Three others had less than 2 years experience. Participants were paid at
the same hourly rate they received for performing their usual job
duties.

## Procedures

Each dispatcher was present in the laboratory for six to eight hours.
Each dispatcher participated in two scenarios, with a different
communication environment each time. Before each trial, dispatchers were
trained on the interface they would use. After the experiment, there was
a short debriefing session.

A short training program was designed to familiarize each participant
with the simulator and the communication environments they would
experience. The training consisted of two phases. In the first phase,
the dispatcher learned how the simulator operated (approximately 30
minutes). During the second phase of training, dispatchers learned the
schedule (approximately 90 minutes).

The voice radio communication equipment was different from what
participants were accustomed to and so training was given. In the data
link environments, training was necessary to introduce the dispatcher to
the data link interface, to gain familiarity with the message tree and
learn the rules (when to alert a train and how to alert it). During this
first training phase, the experimenter explained the routing procedures.
On a training scenario, the dispatcher practiced routing trains (with
eight trains, four inbound trains and four outbound trains, and a yard
move). Then, the experimenter walked the dispatcher through the voice
radio or the data link system. Next, the participant practiced routing
and communicating on the training scenario modified by adding hazards
and MOW requests. During this training, the experimenter sat next to the
dispatcher to answer questions about the system. Dispatchers were given
the structure of the message tree in written form (Appendix A).

During the second phase, the experimenter prepared the dispatcher for
the experimental trials. The experimenter trained each dispatcher on the
schedule for the next scenario. Dispatchers were given up to an hour and
a half to become familiar with the schedule by practicing with the
routing part of the simulator. Familiarization training was repeated
before the second trial, as the scenario was different.

Just before the experiment began, the experimenter reviewed all the
rules (transmission rules for voice radio and message handling for data
link) with the dispatcher. The participant was allowed to use any notes
prepared during the training. The document showing the structure of the
message tree, and the Form Ds were made available. The documents
provided to the dispatchers in addition to the schedule for each
scenario can be found in Appendix D.

Each trial lasted one hour and was interrupted once after 30 minutes to
complete the situation awareness questionnaire. The participant's task
was to perform their usual dispatching task given the constraints
imposed by the new environments. At the conclusion of each trial, the
dispatcher completed a brief questionnaire. Dispatchers were asked to
evaluate workload, comfort with the system, and the usefulness of data
link. Questionnaires for all three environments can be found in
Appendix C. After completing the second trial, the dispatcher also
answered some open-ended questions about the two environments and ranked
the environments by preference.

# RESULTS AND DISCUSSION

## Train Safety

Train safety was evaluated by calculating the ratio of actually alerted
trains to the number of trains that needed to be alerted. Table 5 shows
these ratios for each communication environment.

  --------------------------------- ------------- --------------- ----------------
  []{#__RefHeading___Toc495301880                                 
  .anchor}Table 5. Safety of Trains                               
  and MOW Crews by Communication                                  
  Environment                                                     

                                    Environment                   

                                                  Data link       

  Safety Measure                    Voice Radio   Discrete (%)    Broadcast (%)
                                    (%)                           

  Trains Alerted                    33            45              93

  MOW crews protected               64            94              97
  --------------------------------- ------------- --------------- ----------------

The broadcast data link was the safest environment. The percent of
trains alerted was highest in the broadcast condition, followed by the
discrete data link environment and the radio environment. The
differences observed between the broadcast data link case and the two
other conditions were statistically significant (t~(6)~ = 6.02, p.\< .05
comparing discrete to broadcast data link and t~(6)~ = 9.36, p.\< .05
comparing voice radio to broadcast data link). The better performance of
the broadcast data link case was due to the ease with which multiple
designated trains could be notified. In this environment, dispatchers
were free to broadcast the alerting message to all trains on one branch
or to all trains on their territory. Thus, the dispatcher could alert
all trains entering the hazardous area with only one message. The
drawback of the broadcast environment was that forgetting to send one
alert message endangered multiple trains. In one case, a dispatcher
neglected to warn trains of a hazard, which resulted in 20 percent of
the trains failing to receive the warning. A second drawback could occur
if warnings resulted in false alarms. If the train never encountered the
trespasser, but received the warning, the crew might give less credence
to this type of warning in the future.

In the radio and discrete conditions, the dispatcher alerted each train
individually. If the dispatcher was busy when notified of the hazard,
the dispatcher might delay alerting some or all of the trains. The
differences between the voice radio and discrete data link condition
were not statistically significant. Although the differences were not
statistically significant, the direction of the differences favors the
discrete condition. Dispatchers alerted a greater percentage of trains
in the discrete data link condition than in the voice radio condition.
The train closest to the hazardous area was notified in 83 percent of
the cases for the voice radio, and 100 percent of the cases in the
discrete environment. In the voice radio environment after alerting the
closest train, the dispatchers may have allocated their attention to
other tasks and forgotten to alert the other trains. Alternatively, the
dispatcher's criterion for which trains should be notified in the voice
radio condition may have differed from their criterion in the discrete
data link condition. The dispatcher may have decided that only some
trains traveling on a specific branch were at risk and therefore only
notified the trains perceived to be at risk.

## Mow Safety

Dispatchers normally control the entire track territory for which they
are responsible. However, when maintenance is necessary on or near the
track, dispatchers give temporary control of the track section to the
MOW crew. To make sure the track section under repair is protected, the
dispatcher blocks that track section so that other trains are denied
permission to enter. Trains cannot enter the protected track without the
permission of the MOW crew. However, sometimes there is confusion about
the exact track section the MOW crew requests. For example, where there
are two tracks the MOW crew may request authority to work on track one,
but the dispatcher may inadvertently give them authority to work on
track two. Alternatively, after receiving permission to work on a
section of track, the MOW crew may inadvertently work on unprotected
track instead of the protected track. Both of these situations can
compromise safety for the MOW crew.

The number of MOW crews properly protected during each experiment was
recorded. Whenever dispatchers blocked the track requested or a portion
of track greater than requested, MOW crews were assumed safe. A
dispatcher who granted a track request, but failed to physically block
the track, resulted in an unprotected MOW crew. Table 5 shows the
results in percentages for each environment. In the voice radio
environment, 24 MOW crews were protected properly out of 37. In the
discrete environment, 29 MOW crews were protected properly out of 31,
and in the broadcast environment, 25 out of 26 MOW crews were protected
properly.

Both data link systems were clearly superior to the voice radio
communication environment. The differences observed were statistically
significant (t~(6)~ = 5.98, p. \< .05 comparing voice radio to discrete
data link and t~(6)~ = 7.32, p. \< .05 comparing voice radio to
broadcast data link). The two data link environments did not exhibit a
significant difference. In the voice radio condition, the process of
listening to a track request and transcribing it was time-consuming and
error prone. If the voice radio transmission was unclear, the
dispatchers asked the sender to repeat the message. If an error was
detected during the initial transmission or during the acknowledgement,
the process was repeated. Dispatchers made errors in hearing and
transcribing the message. These kinds of errors are typical of the
errors that occur in voice radio environments. They have also been
documented in the aviation environment (Monan, 1983; Monan 1988; and
Golaszewski, 1989).

In the data link conditions, the MOW foreman (represented by the
experimenter in our study) requested authority to work on selected
portions of the track by sending an email message to the dispatcher. The
location and duration of the track request was displayed in a text
format. The location was also displayed on the track layout display,
color-coded in yellow.

Errors in the data link environment usually came from a peculiarity of
track layout interface. When the dispatcher viewed a message requesting
work authority on a particular section of track, the track layout
interface displayed this information by showing the requested track
section in yellow. When a dispatcher granted a MOW crew's authorization
to work on a track section (blocking the track for use by others), the
track section was color-coded blue on the track layout display. If the
request message was still displayed in the text message window of the
data link interface, the operator could not see if the track was
properly blocked because the yellow color-coding of the MOW request
masked the blue color-coding of the granted authorization.

The results illustrate that a visual display has the potential to
improve safety by minimizing data entry errors and reducing memory load
for the recipient. However, the details of how the interface is
implemented will also impact safety.

## Communication Efficiency

~~The average transaction time for each environment was calculated. The
results are summarized in Table 6. Lower transaction times were observed
for the two data link environments, compared to the radio. The
difference observed between the broadcast data link environment and the
voice radio environment was statistically significant (t~(157)~ = 2.28,
p \< .05, comparing voice radio to broadcast data link). The difference
between the discrete data link and the voice radio condition was not
statistically significant, although the trend was in the same direction
as the broadcast data link condition.~~

  --------------------------------- --------------- ----------- ------------
  []{#__RefHeading___Toc495301881                               
  .anchor}Table 6. Mean Transaction                             
  Completion Time by Communication                              
  Environment                                                   

                                    Environment                 

                                                    Data link   

                                    Voice Radio     Discrete    Broadcast

  Mean Transaction Time (s)         227             174         135
  --------------------------------- --------------- ----------- ------------

### Performance Varies with Message Content

To understand why transaction times were lower for both data link
conditions, the distribution of messages by transaction time was
examined. Figure 9 shows the distribution of message transactions by
time. For all three conditions, the majority of transactions were
completed in two minutes or less. In each condition, there were a small
number of messages that took longer to complete. For the voice radio
condition, there were more of these lengthy transactions compared to the
data link conditions. In the voice radio environment, the percentage of
messages completed after five minutes was 85 percent. By contrast, in
the data link conditions the percentage of messages processed was 97
percent or greater. Thus, some messages took longer to communicate in
the voice radio condition. Similarly, 9 percent of messages were never
answered (presumably forgotten) in the voice radio condition. By
contrast, in the data link conditions, dispatchers forgot significantly
fewer messages. None of the messages were forgotten in the broadcast
condition, and only 1 percent of the messages were forgotten in the
discrete condition.

The difference between voice radio and data link may be partly explained
by the additional memory load required to process messages in the voice
radio condition. Dispatchers were heard asking at least once during each
voice radio condition, "Who was that on the voice radio a couple of
minutes ago?" In the data link interface, the visual display provided an
easy way to remember who called.

[]{#__RefHeading___Toc495302024
.anchor}![](media/image17.wmf){width="5.998611111111111in"
height="2.8868055555555556in"}Figure 9. Number of Transactions by Time
and Environment

To understand what type of message might account for the longer
transaction time, messages were divided into categories by content.
Figure 10 shows the transaction time distribution by the type of
message. The message types included: denied MOW requests, granted MOW
requests, messages between train crews and the dispatcher, miscellaneous
messages, and messages that were not forwarded. Figure 10 shows that
granted MOW requests accounted for the difference between the data link
conditions and the voice radio condition. There were a comparatively
large number of granted MOW requests that took longer than 500 seconds
compared to the two data link conditions.

To clarify the distinction between message types and communication
efficiency in the three communications environments, the communication
transactions were separated into two types depending on the type of
answer. The first type of communication, referred to as simple
communications, included denied MOW requests (i.e., Foul Time), requests
for bulletins on temporary speed restriction bulletins (TSRBs) when
there were none, and the hazard alerts communications. The second type
of communications called complex communications included only one type
of communication - granting a MOW request. In each environment, simple
and complex messages were compared and transmitted as a function of
time. Figure 11 shows the average transaction time for the two
communication types by environment.

As expected, in all three environments the average transaction time was
shorter for simple messages than for complex ones. For simple messages
there were statistically significant differences between the voice radio
condition and the two data link conditions (t~(90)~=3.36, p \< .05
comparing voice radio and direct data link and t~(100)~ = 2.48, p \< .05
comparing voice radio to broadcast data link). In both cases, the
transaction times were lower in the voice radio condition. The average
transaction time was 62 seconds in the voice radio condition compared to
111 seconds in the discrete data link condition, and 161 seconds in the
broadcast data link condition. For complex messages, the voice radio
condition performed worse than the two data link conditions. The average
transaction time was 463 seconds in the voice radio condition compared
to 199 seconds in the discrete data link condition, and 197 seconds in
the broadcast data link condition. Again, these differences were
statistically significant (t~(55)~ = 3.07, p. \< .05 comparing voice
radio to discrete data link and t~(53)~ = 2.95, p. \< .05 comparing
voice radio to broadcast data link). There were no statistically
significant differences between the discrete and broadcast
conditions.![](media/image18.wmf){width="3.948611111111111in"
height="7.479861111111111in"}

[]{#__RefHeading___Toc495302026 .anchor}Figure 11. Mean Task Completion
Time for Simple and Complex Type Messages by Communication Environment

In general, the differences in performance between voice radio and data
link can be related to the way information in different sensory
modalities is processed, and the design of the two communication
interfaces. In the voice radio environment, information was presented in
auditory form. In the data interface, information was presented in a
visual form.

Van Cott and Kinkade (1972) provide guidance on message format. They
indicate that short simple messages are more effectively presented in
auditory form. Lengthy and complex messages are more effectively
presented in visual form. Table 7, adapted from Van Cott and Kinkade
shows the criteria for selecting the form information should take -
either auditory or visual. In the voice radio environment, the simple
messages met several of the criteria for selecting the auditory channel.
The simple messages were generally short addressed events in time that
needed to be acted upon immediately. By contrast, the complex messages
were lengthy and needed to be available to the dispatcher for a longer
period.

The advantage of the data link environments over the radio in processing
complex messages can be attributed to the reduced memory needed to
process information displayed visually. The data link systems gave a
visual representation of train and MOW crew locations in text form and
on the track layout display. MOW crews did not need to repeat which
section of track was needed because of a failure to hear, transcribe, or
understand the track section being described. The dispatcher could read
the information in the text message or see the section requested on the
track layout display color-coded in yellow.

  ----------------------------------- -----------------------------------
  []{#__RefHeading___Toc495301882     
  .anchor}Table 7. Characteristics    
  for Selecting Modality in which to  
  Present Information                 

  **Auditory**                        **Visual**

  Simple                              Complex

  Short                               Long

  Message not referred to later       Message referred to later

  Addresses events in time            Addresses events in space

  Message acted upon immediately      Message not acted upon immediately

  Visual system is overburdened       Auditory system is overburdened

  Environment is too bright or dark   Environment is too noisy
  adaptation is necessary             

  Receiver must move about            Receiver remains stationary

  Adapted from Van Cott and Kinkade   
  (1972)                              
  ----------------------------------- -----------------------------------

By contrast, the dispatcher in the voice radio environment dictated
specific information to MOW workers when they were granted Foul Time
(i.e., dispatcher name, date, time span granted, location, and number of
work crew among others). While the dispatcher dictated the authority to
work on the track, MOW people transcribed the information on paper.
Then, the MOW person acknowledged the transmission by reading back that
same information to the dispatcher. For Form Ds, dispatchers verified
the readback by writing this information on paper. This process was
time-consuming and prone to errors. With the data link interface, the
dispatcher filled in the form directly on the computer and transmitted
the message to the roadway worker. Upon receiving the message, the
roadway worker read and acknowledged the message by sending a written
confirmation back to the dispatcher. The time-consuming process of
listening to the message and repeating it back to the sender was
minimized because the visual display of the work authority was available
to the dispatcher and could be acted upon more quickly.

Favorable comments by the dispatchers indicated that the visual
representation of location information on the track layout display was
particularly helpful in supporting the dispatcher's communication task,
as well as managing the territory. The graphic representation lowered
memory load by making information about the track visible over time. By
displaying this information directly on the track display, the
dispatcher could also see how it would impact the movement of trains or
allocation of track to other MOW crews.

Specific aspects of the visual interface also facilitated the completion
of complex transactions. During the design of the data link interface,
interviews with dispatchers indicated they would not use an interface
that required use of a keyboard to enter information. The development of
message templates facilitated the data entry process. The dispatcher
simply chose the appropriate message type from a menu of message types
and filled in the key information. This procedure minimized transaction
time by reducing the amount of data entry by the dispatcher. A system
that required greater keyboard entry would have reduced the benefits of
the visual interface compared to the auditory interface inherent with
voice radio.

## Situation Awareness

Table 8 shows the percentage of questions answered correctly, and
summarizes the evaluation of situation awareness. While none of the
differences between scores were statistically significant, an
examination of the data is interesting. For voice radio, situation
awareness scores were best for MOW activity followed by hazard
awareness, communications, and routing. For both data link conditions,
situation awareness scores were best for hazard awareness followed by
MOW activity, communications, and routing. For both voice radio and data
link conditions, routing ranked last. This finding suggests that
dispatchers were devoting more resources to communication activities
than to routing activities. Given the higher workload demands associated
with this experiment compared to normal railroad operations, this seems
reasonable. However, it is also reasonable to expect that the
competition for visual resources in the data link condition by the
visual presentation of text might result in a performance decrement in
the data conditions compared to voice radio. Because vision requires
selective attention, the dispatcher can focus on only one display at a
time. However, a performance decrement for data link did not occur.
Routing situation awareness scores were actually better in both data
link conditions, although these differences were not statistically
significant.

For three of the four activities measured, routing, hazard awareness,
and communication performance were better with data link than with voice
radio. The dispatchers demonstrated better knowledge of the train
schedule, current train location, hazard location, and also when
messages were sent and their content. Although the results were not
statistically significant, the trend suggests that data link does not
impair situation awareness compared to the use of voice radio. It may
actually improve situation awareness.

  --------------------------------- ----------------- ------------------ ------------------
  []{#__RefHeading___Toc495301883                                        
  .anchor}Table 8. Situation                                             
  Awareness by Activity and                                              
  Communication Environment                                              

                                    Percent Correct                      
                                    Response by                          
                                    Environment                          

                                                      Data link          

  Activity                          Voice Radio (%)   Discrete (%)       Broadcast (%)

  Routing                           43                63                 63

  Hazards                           57                85                 74

  Communication                     56                71                 66

  MOW activity                      82                85                 72
  --------------------------------- ----------------- ------------------ ------------------

A number of factors may have contributed to the improved performance
trends in the data link conditions for these three measures. The visual
persistence of messages enabled dispatchers to examine this information
at their leisure while lowering memory load at the same time. Displaying
information about routing and hazard location on the track layout
display provided a method for relating this information to the train
schedule. For example, in the data link conditions the dispatchers saw
the hazardous area highlighted in yellow on the track layout display
when they viewed the alerting message. In the voice radio environment,
dispatchers relied on memory to retrieve this information. In current
railroad operations, dispatchers write a personal note or report it in a
"desk book." The visual display found in the data link interface saves
time and resources by avoiding the process of putting this information
in a visual form. By saving the cognitive and physical resources for
other activities, dispatchers can devote more time to other tasks.

For MOW activity, situation awareness scores were similar for voice
radio and data link conditions. Here, situation awareness for voice
radio was slightly worse than the discrete condition and better than the
broadcast condition. Of the four measures of situation awareness, MOW
activity was the measure for which dispatchers showed the best
performance in the voice radio condition. In the voice radio and data
link conditions, the dispatcher made use of a visual display to process
information about MOW activity. In current railroad operations, the
dispatcher must prepare paperwork when granting a MOW request. This
paper work (i.e., Form D) describes in visual form the track location
and time for which the track authority is requested. In our experiment,
dispatchers followed these procedures. Thus, the information received by
voice radio was translated early on into a visual form. When the
dispatcher put the MOW request into effect, this track authority was
also displayed on the track layout display. This provided an additional
visual cue, similar to what was displayed in the data link conditions.
Thus, in both voice radio and data link conditions, a visual aid was
available to assist the dispatcher.

These results suggest that data link does not impair situation
awareness. Overall, a trend towards better situation awareness in the
two data link conditions was observed compared to the voice radio
condition. This improvement was attributed to the lower memory demands
associated with information that was made available in visual form.
Although the visual interface in the data link conditions increased
attention to communication activities, routing situation awareness did
not suffer.

## Productivity

Two measures were used to assess productivity: the number of trains
entering a station late (i.e., with a delay more than five minutes), and
the number of MOW requests granted.

  --------------------------------- ----------------- ------------- ---------------
  []{#__RefHeading___Toc495301884                                   
  .anchor}Table 9. Productivity by                                  
  Communication Environment                                         

                                    Environment                     

                                                      Data link     

  Productivity Measure              Voice Radio (%)   Discrete (%)  Broadcast (%)

  Late Trains                       27                24            13

  MOW requests granted              63                65            54
  --------------------------------- ----------------- ------------- ---------------

Table 9 shows the percent of trains more than five minutes late by
environment and the percentage of MOW requests granted for each
environment. For both measures, the results were not statistically
significant. For both measures, the voice radio and the discrete data
link environment show similar results. The broadcast data link condition
shows the smallest percentage of late trains compared to the two other
conditions. Having fewer alerting messages in the broadcast case might
have lead to more free time to route trains. However, dispatchers
granted fewer MOW requests in the broadcast condition. Overall, the data
suggests that the data link interface did not adversely affect
productivity compared to the voice radio interface.

## Dispatchers' Preferences

The debriefing questionnaire gave the dispatchers an opportunity to
comment on our data link designs as well as on the voice radio
condition. Table 10 summarizes the answers to the debriefing
questionnaires. The numbers in Table 10 represent average scores across
participants on a scale from one to seven. A score of one represents a
low or negative value (low workload, uncomfortable, unrealistic compared
to revenue service). A score of seven represents a high or positive
value (high workload, comfortable, realistic compared to revenue
service). No statistically significant differences were observed.

  --------------------------------- ------------------ -------------- ------------------- --
  []{#__RefHeading___Toc495301885                                                         
  .anchor}Table 10. Dispatcher                                                            
  Ratings of Workload: Comfort and                                                        
  Simulator Realism                                                                       

                                    Environment                                           

                                                       Data link                          

                                    Voice Radio        Discrete       Broadcast           

  Workload                          6.3                6.0            5.8                 

  Comfort                           5.9                5.0            4.3                 

  Realism                           2.1                N/A            N/A                 
  --------------------------------- ------------------ -------------- ------------------- --

The dispatcher rated workload high in all three environments with an
average score around six. The workload was perceived slightly lower in
both data link environments. Dispatchers rated the realism of the voice
radio environment 2.1 out of 7. Dispatchers commented, "No way is a
territory that busy..." One dispatcher said, "No way can a man deal with
that during eight hours. It is totally unrealistic." This rating can be
attributed to the high workload. No dispatcher criticized the voice
radio environment for lack of similarity with the current environment in
respects other than workload.

All dispatchers felt relatively comfortable with the data link
environments (see Table 10). Before the experiment began, most
dispatchers expressed a negative attitude towards data link. However,
after the experiment the dispatchers felt it would be very useful in
addition to voice radio. The dispatchers also gave comments on the use
and implementation of data link. These comments are summarized in Table
11.

  --------------------------------- ---------------------------------------------------------
  []{#__RefHeading___Toc495301886   
  .anchor}Table 11. Dispatcher      
  Comments on the Use of Data Link  

  **Category**                      **Comment**

  Choice of communication channel   Data link would be good for communicating TSRBs (with
                                    speed restrictions announcements), Form Ds for MOW crews
                                    and engineers, Foul Time, train crew and consist
                                    information, car placement information, planned track
                                    outage information, and emergency phone numbers.

                                    Choose voice radio for emergencies and when an immediate
                                    response is required.

  Interface                         A sound alert for incoming messages would be welcome in
                                    the data link environment.

                                    Provide capability to print paper copies of messages.

                                    Distinguish answered from unanswered messages.

                                    Use voice recognition.

                                    The highlighting feature makes a MOW request very clear,
                                    however, blocking actions should remove the yellow color
                                    code.

  Safety                            The dispatcher needs to know whether the recipient read
                                    the message. The acknowledgment procedure requires
                                    further work.

                                    When Foul Time is given back, dispatcher should
                                    acknowledge the message.

                                    Data link allows messages to be acknowledged when one has
                                    the time. There is no audio pressure to respond
                                    immediately.

                                    The broadcast feature could be misused in the same way as
                                    voice radio. MOW crews might take advantage of
                                    information about train and equipment movements to work
                                    without permission.
  --------------------------------- ---------------------------------------------------------

#  {#section-2 .unnumbered}

# CONCLUSIONS

Voice radio congestion is a significant problem in the current
dispatching environment. Data link has been proposed as an alternative
communication channel to solve this problem. In particular, information
presented orally over the radio can be presented in visual (text and
graphic) or aural form with data link. The objective of this study was
to evaluate how the introduction of data link technology might affect
dispatcher performance. The results suggest that data link can improve
communication efficiency without adversely affecting productivity,
situation awareness, or safety. Even where the results were not
statistically significant, they favored data link. Compared to voice
radio, data link improved safety and situation awareness. For
productivity, no statistically significant differences were observed
between data link and voice radio.

Data link improved safety compared to the voice radio. In data link,
dispatchers protected a greater percentage of trains and MOW crews
compared to the voice radio. By providing information in a visual
format, data link eliminated readback errors and hearback errors
associated with the auditory modality. Eliminating these errors helped
shorten the duration of complex, safety critical messages like temporary
speed restrictions. Translating track requests from alphanumeric text to
a graphic display on the track layout display made the request even
easier to process. The visual nature of information presented in the
data link systems reduced the demand placed on the dispatcher's memory.
The dispatchers were much less likely to forget to respond to messages
with data link than with voice radio. Anecdotal comments by the
participants suggested it also reduced stress by providing a quieter
environment in which to work, giving the dispatcher greater control over
when messages were answered.

Communicating information in visual form did not negatively impact
situation awareness scores. Where the differences between the data link
and voice radio conditions were not statistically significant, the
trends showed a positive impact for data link. Situation awareness
scores for both data link conditions were better than voice radio for
routing, hazard awareness, and communication. While the dispatcher
devoted more resources to processing visual information with the data
link conditions than with voice radio, (there were three displays to
monitor instead of two), no adverse impact was evident. The dispatcher
appeared to benefit by having a visually persistent display of
information that reduced memory load. MOW activity was the only category
in which performance was as good or better than the voice radio
condition. Dispatchers had a visual form of information to assist them
in situation awareness. In the voice radio condition, dispatchers wrote
the track requests on paper as part of the track authorization process,
which helped in acknowledging the request. This finding reinforces the
importance of the visually persistent forms of information in supporting
the dispatcher in processing complex information.

Overall, the differences between the discrete data link condition and
the broadcast data link condition were small. The broadcast version
showed a greater improvement in train safety than the discrete version.
The broadcast version minimized communication workload by providing a
simple way to reach multiple recipients and freed the dispatcher to
attend to other tasks. For example, the dispatcher could use a single
message to alert all trains along a particular branch. The discrete
system required the dispatcher to contact each train individually.

However, implementing broadcast data link in revenue service will
require addressing two issues related to information distribution and
acknowledgment procedures. If a dispatcher failed to send a message as
happened in one instance, or the message failed to reach the intended
recipients, the consequences were larger since multiple parties were
affected. Failure to send a single message placed multiple trains at
risk. Thus, a single error can increase the risk of harm, compared to a
system that only allows messages to be sent to one party at a time.
System designers will need to consider how to minimize the impact of
these types of errors.

A second issue for broadcast data link concerns acknowledging the
receipt of messages. Acknowledgement means that the train crew has read
and understood the message. Since dispatchers alert multiple trains
simultaneously, they need to determine whether all trains received the
message. Therefore, the dispatcher will need a method to keep track of
acknowledgments. Designing the data link interface to support tracking
of multiple acknowledgements will be an important requirement.

Communication efficiency for voice radio and the two data link
conditions varied as a function of the characteristics of each medium.
Information communicated by voice radio was presented in an auditory
format. Information communicated via data link was presented in a visual
format. Each form proved better suited for presenting some kinds of
information than others. Voice radio proved to be better suited for
communicating short and informal communications as well as time-critical
messages that required immediate action (i.e., a dispatcher reporting no
speed restrictions when a locomotive engineer called to request a
temporary speed-restriction bulletin or alerting a locomotive engineer
to the presence of a trespasser). For these types of communications,
data link doubled the communication times over voice radio. These
results were due to the auditory format in which the information was
presented.

In this experiment, data link proved better suited for communications
whose length or complexity imposed a significant burden on memory. In
railroad operations, these characteristics are typical of safety
critical messages that require formal acknowledgement procedures (i.e.,
granting a Foul Time request or authorizing a train movement using a
Form D). Data link provided an efficient channel for these
communications; transaction times were reduced by a factor of two. The
idea of not having to repeat a message multiple times was also appealing
to the dispatchers in our study.

In voice radio and data link conditions, the differences observed
between the two types of messages were due to the modality or format in
which the information was presented, not the communication medium. While
information sent over the radio is presented in an auditory form,
digital communications systems like data link afford more presentation
options. Thus, data link supports both auditory and visual modalities.
The properties listed in Table 7 suggest what format a message should
take.

The differences identified between voice radio and data link also
depended upon the details of how each interface was implemented. Had the
data link interface required the dispatcher to make more use of the
keyboard to enter messages than with the current design, the results
might have been quite different. Pilot testing indicated that heavy use
of a keyboard was unacceptable to the dispatcher population, and would
have resulted in longer response times. Similarly, the ability to show
track-related information in text or graphic format reduced
communication errors and dispatcher response time. This feature also
generated positive comments from the dispatchers. Successful
implementation of a data link interface is dependent upon applying
principles of good human factors design and usability testing to meet
the needs of dispatchers who use this communication interface.

The current study suggests that dispatchers benefit from both voice
radio and data link communication modes. In recommending the conditions
under which medium should be used, this study suggests that voice radio
is best suited for communicating simple, time-sensitive messages to one
recipient. Data link system is best suited for communicating lengthy
messages. Sending discrete messages works best where privacy is
important or the message content would benefit only the recipient for
which the message is intended. Sending broadcast messages works best
when there is a need to communicate the same information to multiple
recipients.

##  Future Research

This study suggests that data link technology has the potential to
improve the safety and communication efficiency of the dispatching
environment. However, the introduction of new technology and new
interfaces raises new issues along with solving old problems. The
current study compared voice radio to data link where each was the only
medium. However, in actual operations both types of communication
systems will be available. Currently, data link affords more flexibility
in terms of how information is presented. The challenge for designers of
future railroad communication and information systems will be deciding
the format that different kinds of information should take.

As an example, consider the acknowledgment procedures for granting train
movements or authorizing track use by MOW crews. For safety reasons, the
acknowledgment procedure is needed to assure the sender that the message
was received and understood. This issue is particularly important for
messages concerning train movement authorization and track allocation
procedures that are governed by formal operating procedures. The kinds
of errors associated with the verbal acknowledgement procedures are less
likely to occur when this information is presented in a visual format.
Nevertheless, different methods of entering information (e.g., keyboard,
mouse, or touch screen) will create new errors as well. Keyboard entry
may result in transposition errors while mouse and touch screen entry
may contribute to selection errors. Identifying these error types will
be important to their mitigation.

Another example concerns how dispatchers allocate their attention to
incoming messages. The temporal nature of messages received by voice
radio calls for an immediate response by the dispatcher. In practice,
however, the dispatcher does not immediately answer all calls (Roth,
Malsch, and Multer, 2001). The dispatcher constantly evaluates whether
to continue with the current task or switch to a different activity.
When there is more than one call to answer, the dispatcher must decide
which call will be attended to first. In this experiment, simples
messages from train crews were acted upon more quickly than messages
from MOW crews requesting track in the radio condition. This behavior
was not observed with data link. Did the lower workload associated with
granting a MOW request in the data link condition change how the
dispatchers allocated their attention? How will dispatchers allocate
their attention when voice radio and data link are used together? More
research will be needed to understand how the use of both voice radio
and data link impacts the dispatcher's attention allocation.

Several related challenges for designers will come from the increasing
complexity of these information systems. By increasing the bandwidth
over which information is communicated, data link will increase the
quantity of information available to the dispatcher. To handle the
increasing quantity of information, the interface for managing this
information and railroad operations will also increase in complexity.
Data link technology offers the ability to create public (shared) and
private communication channels. What information should remain private
and what information should be shared? For shared communication, how
much information can be communicated before the operator becomes
overloaded? How should the interface be designed to address information
overload?

Both visual and auditory interfaces have limits to the amount of
information that can be effectively displayed. Thus, large amounts of
information may be hidden from the dispatcher. One challenge concerns
getting lost in this information space (Elm and Woods, 1985; Woods,
Roth, Stubler, and Mumaw, 1990; and Burns, 2000).

A second challenge concerns the management of the interface itself. As
the information space increases in size, more cognitive resources will
be devoted to dealing with the interface. Fewer resources will be
devoted to cognitive activities directly associated with the operational
task (e.g., deciding whether to authorize a train movement). Designers
will need to carefully consider how the interface design impacts the
dispatcher's ability to quickly find information so that attention
remains on the operational task.

Finally, it is unclear from our results to what extent dispatchers are
affected by the loss of information they acquire over voice radio that
is not specifically directed to them. Roth, Malsch, and Multer (2001)
observed that dispatchers in actual railroad operations took advantage
of information overheard on the radio but not intended for them. The
participants in this study did not appear to make use of this additional
information. Further research will be necessary to determine the need
for information now available through the party line and how that
information could be provided in a data link system.

# APPENDIX A. MESSAGE TREES {#appendix-a.-message-trees .Appendix-1}

This appendix shows the message trees for the dispatcher and
experimenter. In addition, the distribution list used by the dispatcher
to specify the group of secondary recipients in the data link broadcast
environment was included.

The Dispatcher Message Tree Used During the Experiment

<table style="width:100%;">
<colgroup>
<col style="width: 22%" />
<col style="width: 4%" />
<col style="width: 2%" />
<col style="width: 11%" />
<col style="width: 11%" />
<col style="width: 7%" />
<col style="width: 3%" />
<col style="width: 14%" />
<col style="width: 0%" />
<col style="width: 20%" />
</colgroup>
<tbody>
<tr class="odd">
<td colspan="7"><strong>High Priority</strong></td>
<td colspan="3"></td>
</tr>
<tr class="even">
<td colspan="7"><em>To Engineer- Fatalities</em></td>
<td colspan="3"></td>
</tr>
<tr class="odd">
<td colspan="3">Trespasser hit</td>
<td colspan="4">Train derailment</td>
<td colspan="3"></td>
</tr>
<tr class="even">
<td colspan="3"><p>Notified RT – protection set up.</p>
<p>Med. Assistance – help underway.</p></td>
<td colspan="4"><p>Notified RT help underway.</p>
<p>To other trains – routing delays.</p>
<p>To MOW – train derailed –busy time.</p></td>
<td colspan="3"></td>
</tr>
<tr class="odd">
<td colspan="7"><em>To Rescue Team</em></td>
<td colspan="3"></td>
</tr>
<tr class="even">
<td colspan="3">Trespasser hit</td>
<td colspan="4">Train derailment</td>
<td colspan="3"></td>
</tr>
<tr class="odd">
<td colspan="3">Alert rescue team.</td>
<td colspan="4">Alert rescue team.</td>
<td colspan="3"></td>
</tr>
<tr class="even">
<td colspan="8"><strong>Medium Priority</strong></td>
<td colspan="2"></td>
</tr>
<tr class="odd">
<td colspan="8"><em>To Engineer – Danger Warning</em></td>
<td colspan="2"></td>
</tr>
<tr class="even">
<td colspan="2">Trespasser</td>
<td colspan="3">Obstruction – train stalled</td>
<td colspan="3">Kids throwing stones</td>
<td colspan="2"></td>
</tr>
<tr class="odd">
<td colspan="2"><p>Trespassers on track ahead.</p>
<p>Trespassers are gone.</p>
<p>Trespassers have been taken care of.</p></td>
<td colspan="3"><p>Vehicle on track.</p>
<p>Train stuck on track.</p>
<p>Information request about stalled train.</p>
<p>Locomotive is coming.</p></td>
<td colspan="3"><p>Kids are playing.</p>
<p>Kids are gone.</p></td>
<td colspan="2"></td>
</tr>
<tr class="even">
<td colspan="5"><em>To MOW –Danger Warning</em></td>
<td colspan="3"></td>
<td colspan="2"></td>
</tr>
<tr class="odd">
<td colspan="5">NOW on the wrong track</td>
<td colspan="3"></td>
<td colspan="2"></td>
</tr>
<tr class="even">
<td colspan="5">Notification</td>
<td colspan="3"></td>
<td colspan="2"></td>
</tr>
<tr class="odd">
<td colspan="8"><strong>Low Priority</strong></td>
<td colspan="2"></td>
</tr>
<tr class="even">
<td colspan="8"><em>To Engineer – Standard Communication</em></td>
<td colspan="2"></td>
</tr>
<tr class="odd">
<td>Temporary Speed Restrictions (TSR)</td>
<td colspan="3">Track Problem</td>
<td colspan="2">State of Engine</td>
<td colspan="4">Special Train Movement</td>
</tr>
<tr class="even">
<td><p>No TSRB</p>
<p>TSRB follows</p>
<p>TSRB update</p>
<p>Special speed restrictions</p></td>
<td colspan="3"><p>Track repaired – reduced speed</p>
<p>Track out of service – delay and reroute</p></td>
<td colspan="2">Special routing due to risk of total failure</td>
<td colspan="4">Special movement</td>
</tr>
<tr class="odd">
<td colspan="4"><em>Dispatcher to MOW – Standard Communication</em></td>
<td colspan="5"><em>To Yard Routing preferences</em></td>
<td><em>To Lifting Bridge</em></td>
</tr>
<tr class="even">
<td>Track Work</td>
<td colspan="3">Signal Work</td>
<td colspan="2">Track Wishes</td>
<td colspan="3">Need Locomotive</td>
<td>Bridge Lifting</td>
</tr>
<tr class="odd">
<td><p>Foul Time granted.</p>
<p>Foul Time refused.</p>
<p>Other Foul Time proposal</p>
<p>Foul Time ends.</p></td>
<td colspan="3"><p>Foul Time granted.</p>
<p>Foul Time denied.</p></td>
<td colspan="2"><p>Not possible – other track or wait.</p>
<p>Okay for required track.</p></td>
<td colspan="3">Can we have a locomotive?</td>
<td><p>Okay to lift bridge.</p>
<p>Impossible to lift bridge.</p></td>
</tr>
</tbody>
</table>

Broadcast Group Selection

The broadcast group selection has two layers. The first layer is the
type of recipient and the second is the location of these recipients.
The broadcast group selection tree used in the experiment has the
following structure:

(Recipient) [Trains]{.underline}

(Location) *On branch A*

*On branch B*

*On branch C*

*On branch D*

*All*

Trains and MOW

*On branch A*

*On branch B*

*On branch C*

*On branch D*

*All*

MOW

*On branch A*

*On branch B*

*On branch C*

*On branch D*

*All*

Everybody

Experimenter's Message Tree

[ENGINEER MESSAGE TREE]{.underline}

[High priority]{.underline}

*Engineer to Dispatcher*

Trespasser hit

Train hit a trespasser

Medical help is needed

Passenger dead/injured

Assistance in station

Assistance right away?

Train derailed

Need help

[Medium priority]{.underline}

*Engineer to Dispatcher*

Trespasser

Seen on track

Engine failure

Train stuck on track

Freight train stuck

Power insufficient -- need power/loco

Threat for people in the train

Chemicals released

Bomb on the track

Kids throwing stones

Kids throwing stones

Not there any more

Obstruction

Engine failure - train stuck on track

Trees across the track

No trees any more

Additional locomotive needed -- freight train

Failures

Total power loss -- Train stuck

In cab system failure

Re-crewing

Crew outlawed

Re-crewing position OK

What is up?

Need information -- What are you doing?

[Low priority]{.underline}

*Engineer to Dispatcher*

Engine state

Engine OK

Engine state -- serious trouble

Track problem

Track damaged

Bad weather

Thunderstorm -- reduce speed

Leaves on the track -- reduce speed

Special events

Dignitaries on the train

Bulletin

Bulletin request

Warning

Long/large/high train!

Position report

Current position

*Engineer to Support staff*

Engine state

Engine OK

Engine state -- serious trouble

[MISCELLANIOUS MESSAGE TREE]{.underline}

[High priority]{.underline}

*Police to Dispatcher*

Police intervention

Stop the train

Corpse near the track

*Rescue Team to dispatcher*

Fatality

Everything under control

Train derailment

Everything under control

Passenger dead/injured

Everything under control

MOW fatality/injury

Everything under control

*System to Dispatcher*

MOW in danger

Protection forgotten

Gave Foul Time but unprotected!

[Medium priority]{.underline}

*System to Dispatcher*

MOW person on the wrong track

Worker not protected

Trespasser

Trespasser on track

Obstruction

Vehicle stranded on grade crossing

Unprotected station

Station with no bridge crossing

Electrification problem

Power cable failure

Loss of electrification/power

Re-crewing

Crew outlawed

Loco power problem

Power insufficient

CETC problem

Not updating -- shift to radio communication

Field signal problem -- messaging routing

*Electrification Department to Dispatcher*

Power loss

Power outage on track.

Power problem repaired

[Low priority]{.underline}

*System to Dispatcher*

Engine state

Engine OK

State of the engine -- serious trouble

Information

Rescue operation -- World information

Unprotected station -- World information

Notified - Height limitation on given track

Notified - Speed limitation on given track

Emergency phone numbers

Special events

Dignitaries on train

Special train

Special car

Delays

Slow crew

Scheduled meet not possible

Bulletin

Bulletin request

Warnings

Long/large/high train!

Operation at limit capacity

Reminder -- Train priorities

Signal workers on track

Two meets and passes at same time

Time to recover - alert

Possible dispatching mistakes

Omitted a warning

Unnecessary route cleared

Routing mistake -- Lack of protection?

Too much track given away

Routing mistake -- No power!

*Yard to Dispatcher*

Train servicing

Request particular track

*System to Engineer*

Engine state

Engine OK

State of the engine -- serious trouble

Bulletin

No bulletin

Bulletin -- restrictions

Bulletin -- update

*Bridge Lifting to Dispatcher*

Bridge Lifting

Ship waiting for bridge

The ship passed

[MOW MESSAGE TREE]{.underline}

[High priority]{.underline}

*MOW to Dispatcher*

MOW fatality/injury

Railroad person dead (heart attack)

Medical assistance needed

[Medium Priority]{.underline}

*MOW to Dispatcher*

Track Work

Track Work permission request

Track Work protection request

Work completed

Additional time requested

Signal Work

Signal Work permission request

Signal Work protection request

Track car failure

Track car stuck

Track car out of the way

Track problem

Track damaged

Work performed -- Speed restrictions

Power loss

Power outage on track.

# APPENDIX B. EVENT SCHEDULES {#appendix-b.-event-schedules .Appendix-1}

Appendix B contains the schedules for the trains, hazards, and MOW work.
The train schedule was provided to dispatchers during the experiment.

The following is the train schedule for Scenario #1

![](media/image21.png){width="6.0in" height="3.9451388888888888in"}

![](media/image23.png){width="6.0in" height="4.022916666666666in"}The
following is the train schedule for Scenario #2

![](media/image24.png){width="5.999305555555556in"
height="4.095138888888889in"}

The following is the hazard schedule for scenario #1 (with MOW crew
calling times). The gray area indicates the presence of a trespasser in
a specific area of the track. Under each hazard are the identification
numbers of the trains that would pass through this area if the trains
ran on schedule. The first number in the gray area represents the number
of the "alerter train"; the other numbers in the gray area represent the
trains the dispatcher had to alert.

![](media/image25.wmf)

The following is the hazard schedule for scenario #2 (with MOW crew
calling times)

![](media/image26.wmf)

The following are the MOW schedules respectively for scenario #1 and
scenario #2

![](media/image27.wmf)

![](media/image28.wmf)

# APPENDIX C. QUESTIONNAIRES {#appendix-c.-questionnaires .Appendix-1}

Appendix C includes all the questionnaires: the situation awareness
questionnaire, the post-experiment questionnaires for all three
environments, and the final debriefing questionnaire.

**Situation Awareness Questionnaire**

Please answer the following questions as best as you can. Keep your
answers as short as possible. You will have very little time and will
not be allowed to use the dispatching system; hence, you are not
expected to answer all questions properly.

1.  What is the number of the most delayed train?

2.  Can you estimate the time delay for that train?

3.  What is the number of the least delayed train?

4.  Can you estimate the time delay for that train?

5.  When is your next train due out of the terminal?

6.  Do you see any routing conflicts?

7.  Do you have "hazards" somewhere on the territory?

8.  Where?

9.  Any particular restrictions on the track usage?

10. Where are your MOW crews?

11. Which MOW crew will complete its work next?

12. What track could you give away for a 15 minute span to a MOW crew?

13. Whom did you last talk to?

14. When did you last talk?

15. What was the subject of your communication?

16. What was the last message you heard that wasn\'t intended for you
    directly? (used only in the radio environment and in the DB
    environment)

## Post Experiment Questionnaire {#post-experiment-questionnaire .Appendix-2}

Radio environment

Please answer the following questions as best as you can. If you have
any problems, we are here to help. Don't feel limited by the questions.

-   Did you route before answering the messages, answer messages before
    routing, or neither -- it depends on the situation?

```{=html}
<!-- -->
```
-   How realistic do you think the replica of the radio environment?

> [Very Unrealistic]{.underline} [Very Realistic]{.underline}
>
> 1 2 3 4 5 6 7

-   How would you rank the workload during the experiment?

> [Very Low]{.underline} [Very High]{.underline}
>
> 1 2 3 4 5 6 7

-   How comfortable were you in the radio communication environment?

> [Very Uncomfortable]{.underline} [Very Comfortable]{.underline}
>
> 1 2 3 4 5 6 7

-   Any suggestions to make the system better. Improvements. Any comment
    is welcome. Feel free to write anything, especially critiques!

DD environment

-   Would you like the data link directed environment in addition to
    your current radio environment? Why?[^3]

```{=html}
<!-- -->
```
-   Did you route before answering the messages, answer messages before
    routing, or neither -- it depends on the situation?

```{=html}
<!-- -->
```
-   How would you rank the workload during the experiment?

> [Very Low]{.underline} [Very High]{.underline}
>
> 1 2 3 4 5 6 7

-   How comfortable did you feel with the data link directed system?

> [Very Uncomfortable]{.underline} [Very Comfortable]{.underline}
>
> 1 2 3 4 5 6 7

-   How helpful would it be to have such data link capacities in your
    current environment?

> [Very Unhelpful]{.underline} [Very Helpful]{.underline}
>
> 1 2 3 4 5 6 7

-   Any suggestions to make the system better. Improvements. Any comment
    is welcome. Feel free to write anything, especially critiques!

DB environment

-   Would you like the data link broadcast environment in addition to
    your current radio environment? Why?

```{=html}
<!-- -->
```
-   Did you route before answering the messages, answer messages before
    routing, or neither -- it depends on the situation?

```{=html}
<!-- -->
```
-   How would you rank the workload during the experiment?

> [Very Low]{.underline} [Very High]{.underline}
>
> 1 2 3 4 5 6 7

-   How comfortable did you feel with the data link broadcast system?

> [Very Uncomfortable]{.underline} [Very Comfortable]{.underline}
>
> 1 2 3 4 5 6 7

-   How helpful would it be to have such data link capacities in your
    current environment?

> [Very Unhelpful]{.underline} [Very Helpful]{.underline}
>
> 1 2 3 4 5 6 7

-   Any suggestions to make the system better. Improvements. Any comment
    is welcome. Feel free to write anything, especially critiques!

## Final Debriefing Questionnaire {#final-debriefing-questionnaire .Appendix-2}

Please answer the following questions as best as you can. If you have
any problems, we are here to help. Don't feel limited by the questions.

-   Which environment did you like most (Data link Directed, Data link
    Broadcast or radio)? Why?

-   Would you like the data link directed system in addition to your
    current radio environment? Why?

-   Could you please rank the following starting with the best?

> Radio only
>
> Data link Directed only
>
> Data link Broadcast only
>
> Radio and Data link Directed
>
> Radio and Data link Broadcast

-   Would any environment be good for training? Why?

-   Any suggestions to make the system better. Improvements. Any comment
    is welcome. Feel free to write anything, especially critiques!

# APPENDIX D. EXPERIMENT DOCUMENTS  {#appendix-d.-experiment-documents .Appendix-1}

Appendix D contains all the documents provided to the dispatcher during
the two one-hour experiments, except the train schedules and the message
tree structure. Train schedules for the experiments can be found in
Appendix B and the message tree structure can be found in Appendix A. In
order, we have the explanatory text for the use of the simulator, the
train schedule for the training scenario, the transfer sheets, the
Form D sheets, and the Foul Time sheets.

## Simulator quick user's manual {#simulator-quick-users-manual .Appendix-2}

[About the routing:]{.underline}

1.  A red track is a track occupied by a train. When there is no train,
    the track is white.

2.  Every train leaving the terminal has to be sent a bulletin before
    he/she can leave. Assume that, in any other station, the train has
    already started the ride and received a TSRB.

3.  To clear the route, click first on the "clear route" button at the
    bottom of the screen. Then click on the entry and exit signals of
    the interlocking according to the route you want the train to take.
    The color of the track changes to green.

4.  To unclear a route, click first on the "unclear" button at the
    bottom of the screen. Then click on entry or exit signal of the
    interlocking according to the route you want the train to take. The
    color of the track changes back to white.

5.  The route will unclear automatically if a train has used it. The
    color of the track will change back to white.

6.  To block a route for MOW activity, click first on the "block" button
    at the bottom of the screen. Then click on the part of the track you
    are giving away. You have to repeat the process if you want to block
    more track.

7.  To unblock a route, click first on the "unblock" button at the
    bottom of the screen. Then click on the part of the track you want
    to unblock. You have to repeat the process if you want to unblock
    more track.

[Names:]{.underline}

The territory has four main branches named A, B, C, and D respectively.
Stations on these branches have the name of the branch. There are four
stations: station A, station BR, station BL, and station D.

Interlockings have names composed of a letter (the branch) and a number,
the number representing the order of the interlocking from left to
right.

To identify blocks during communications, we use a set of three
elements. First, the general position i.e. the interlocking, the station
or interlockings on the left and on the right. Second, the number of the
track - knowing that tracks are numbered from top to bottom and third,
the number of the block.

[About the messaging system:]{.underline}

1.  The message console is divided in two parts: the left window handles
    received messages and the right window shows the messages that were
    sent out. In each of these windows, there are two elements: a list
    of all appropriate messages and the message, currently highlighted
    in the list displayed at the bottom of the window.

2.  The dispatcher would answer a message by pressing the "send message"
    or "reply" button, and a list of preprogrammed messages will appear.
    These messages are sorted into a message tree. The tree has four
    levels: the priority, the recipient, the subject of the message and
    the preprogrammed message itself. A layout of the tree will be
    provided and explained to you.

3.  To fill in the blanks in the messages, you can use either the
    keyboard or the mouse. Most blanks can be specified by double
    clicking on the adequate field and by clicking the target train or
    by using the keyboard directly (without double-click). This is valid
    for train numbers, MOW crew identifiers, and name of block to be
    worked on. The cursor automatically moves from one field to the
    next. When a message is highlighted, i.e., read, the blocks
    specified in the text of the message turn yellow on the routing
    screen.

[About the work allocation:]{.underline}

There are two groups of messages related to work request. Each group is
described below:

1.  **Track work**- Track Cars or Repair Crews usually perform track
    work. We expect the dispatcher to answer their request using the
    correct branch of the message tree. The type of work will be
    indicated in the work request message.

2.  **Signal work**- Signal Workers usually perform repairs on signal.
    They expect to receive answers from the signal work sub tree. Here
    again the type of work in the request message will help decide which
    branch of the tree to use.

About the message "replying," sending, and forwarding requirements:

1.  Any update about hazards has to be transmitted to all other trains
    scheduled to ride the branch on which the hazard is located. These
    messages include: trespasser on the track and trespasser are gone,
    kids throwing stones and kids are gone, and finally, bad weather
    zone and bad weather zone is gone.

2.  Overweight events and engine state messages are for your personal
    information.

## Training Scenario Train Schedule {#training-scenario-train-schedule .Appendix-2}

![](media/image29.png){width="5.999305555555556in"
height="2.113888888888889in"}

## Transfer Sheets {#transfer-sheets .Appendix-2}

Dispatchers take over the track given away by the previous dispatcher on
the shift when they start their experiment. Dispatchers also get written
information about the scheduled work during their shift. This
information is usually found on a transfer sheet. The following are our
transfer sheets (Note that the only similarity with the real world is
the name and the type of information. The same is true for the Form Ds
that follow.).

Transfer Sheet for scenario #1

Scheduled work information (provided when the dispatcher start the
experiment):

1.  Track outage is scheduled at 1:30 p.m. between interlocking B1 and
    B2 on track 1 and track 2 block 2, at interlocking B2 T11, at
    interlocking B2 T12, and at interlocking B2 T22 block 1. Repair Crew
    #3 will ask for protection around 1:25 p.m. Form D required.

2.  Track outage is scheduled at 1:30 p.m. between interlocking C4 and
    C5 on track 3 block 1 and at interlocking C5 T33 block 1. The MOW
    crew will ask for protection around 1:25 p.m. Form D required.

Please follow the platform indications as closely as possible. As at
South Station, some trains have a longer consist and might not fit
everywhere. The schedule has been drafted accordingly. Also, you might
want to pay particular attention to the incoming train appearing during
the simulation given that you don't have a big overview display.

Transfer Sheet for scenario #2

Scheduled work information (provided when the dispatcher starts the
experiment):

1.  Track outage is scheduled at 4:38 p.m. at interlocking C4 T32,
    interlocking C4 T22, block 2, and interlocking C4 T33, block 2.
    Repair Crew #8 will ask protection around 4:33 p.m. Form D is
    required in the radio environment.

2.  Track outage is scheduled at 4:19 p.m. between interlocking B1 and
    B2 on track 3 block 1 and 2 and on track 4 block 1 and 2. Repair
    Crew will ask for protection around 4:15 p.m. Form D is required in
    the radio environment.

Please follow the platform indications as closely as possible. As at
South Station, some trains have a longer consist and might not fit
everywhere. The schedule has been drafted accordingly.

Also, you might want to pay particular attention to the incoming train
appearing during the simulation given that you don't have a big overview
display.

## Form D {#form-d .Appendix-2}

**Form D**

Work Crew \# \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Date Dispatcher's name

Starting Time Ending Time

Location

##   {#section-3 .Appendix-2}

## Foul Time form {#foul-time-form .Appendix-2}

**Foul Time Request**

Work Crew \# \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

Date Dispatcher's name

Starting Time Ending Time

Location

# GLOSSARY {#glossary .Appendix-1}

**Block:** A length of track with defined limits on which train
movements are governed by block signals, cab signals, or Form D.

**Broadcast data link:** A form of data link in which a message is sent
to multiple designated parties.

**Cognitive Task Analysis (CTA):** Analysis of the cognitive demands of
a complex task. This includes the knowledge, mental processes, and
decisions that are required to perform the task. The goals of a CTA are
(1) to identify what factors contribute to cognitive performance
difficulty; (2) to uncover the knowledge and skills that expert
practitioners have developed to cope with task demands; and (3) to
specify ways to improve individual and team cognitive performance in a
domain through new forms of training, user interfaces, or decision-aids.

**Consist:** The make-up of a train, including locomotives and cars.
Also described by its locomotive power, tonnage, number, and type of
cars, and location and type of hazardous materials.

**Crossover:** A combination of two switches connecting two adjacent
tracks. When aligned, this switch combination allows movements to cross
from one track to the other.

**Centralized Traffic Control (CTC**)**:** A signal system that allows
the dispatcher to know which blocks are occupied by trains and roadway
workers, and to control switches and signals remotely from the dispatch
center.

**Data link:** A digital communications capability which supports moving
information between office-based and field-based computers and their
operators. In the railroad environment, operators include: dispatchers,
train crews, and roadway workers. Information is digitally coded and
messages can be discretely addressed to individuals or multiple
recipients. Information can be presented in multiple sensory modalities
(e.g., visual or auditory).

**Discrete data link:** A form of data link in which a message is sent
to a single party.

**Form D:** A track usage authority form that is issued by a railroad
dispatcher. A Form D contains written authorization, restrictions, or
instructions issued by the dispatcher to specified individuals. Form Ds
permit trains and other track users to occupy specific segments of track
identified by the railroad dispatcher.

**Foul Time:** Time during which track is temporarily obstructed for
work on or around the track. The term "Foul Time" is used by railroads
that follow the NORAC operating rules. Other railroads use different
terms (e.g., track and time) to refer to the same condition.

**Interlocking:** A configuration of switches and signals interconnected
to direct trains along different routes, the limits of which are
governed by interlocking signals.

**Maintenance-of-Way (MOW):** On-track maintenance for repairing,
testing, and inspecting track or wayside apparatus such as signals and
communication devices.

**NORAC:** Northeast Operating Rules Advisory Committee.

**Operating Rules:** A book of rules that govern a particular railroad's
operating procedures and practices.

**Roadway worker:** Any employee of a railroad or of a contractor to a
railroad whose duties include the inspection, construction, maintenance
or repair of railroad track, bridges, roadway, signal and communication
systems and electric traction systems on or near the track. This
definition also applies to employees or contractors who have the
potential to foul the track and employees responsible for their
protection.

**Shunt:** Activate automatic block or interlocking signals when present
on track.

**Territory:** A section of railroad for which a dispatcher is
responsible for the safe and efficient movement of trains and other
on-track equipment.

**TGV:** Train à Grande Vitesse, the French high-speed train.

**Track car:** Equipment, other than trains, operated on a track for
inspection or maintenance. Track cars might not shunt track circuits.

**Track and Time:** Time during which track is temporarily obstructed
for work on or around the track. Other railroads use different terms
(e.g., Foul Time) to refer to the same condition.

**TSRB:** Temporary Speed Restriction Bulletin(s).

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[^1]: The track is not displayed to scale.

[^2]: The dispatcher could alert trains that did not need alerts.
    Participants received no credit when this event occurred, nor were
    they penalized.

[^3]: The term discrete was used in place of directed in the body of the
    report because it more aptly describes the characteristics of this
    data link environment.