+---------------------+----+----------+----------+---+---+---+-------------+
| # REPORT            |    |          |          | * |   |   |             |
|  DOCUMENTATION PAGE |    |          |          | F |   |   |             |
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|                     |    |          |          | O |   |   |             |
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|                     |    |          |          | N |   |   |             |
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|                     |    |          |          | . |   |   |             |
|                     |    |          |          | 0 |   |   |             |
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|                     |    |          |          | 4 |   |   |             |
|                     |    |          |          | - |   |   |             |
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|                     |    |          |          | * |   |   |             |
+---------------------+----+----------+----------+---+---+---+-------------+
| 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     |    |          |          |   |   |   |             |
| other aspect of     |    |          |          |   |   |   |             |
| this collection of  |    |          |          |   |   |   |             |
| information,        |    |          |          |   |   |   |             |
| including           |    |          |          |   |   |   |             |
| suggestions for     |    |          |          |   |   |   |             |
| reducing this       |    |          |          |   |   |   |             |
| burden, to          |    |          |          |   |   |   |             |
| Washington          |    |          |          |   |   |   |             |
| Headquarters        |    |          |          |   |   |   |             |
| Services,           |    |          |          |   |   |   |             |
| Directorate for     |    |          |          |   |   |   |             |
| Information         |    |          |          |   |   |   |             |
| Operations and      |    |          |          |   |   |   |             |
| Reports, 1215       |    |          |          |   |   |   |             |
| Jefferson Davis     |    |          |          |   |   |   |             |
| Highway, Suite      |    |          |          |   |   |   |             |
| 1204, Arlington, VA |    |          |          |   |   |   |             |
| 22202-4302, and to  |    |          |          |   |   |   |             |
| the Office of       |    |          |          |   |   |   |             |
| Management and      |    |          |          |   |   |   |             |
| Budget, Paperwork   |    |          |          |   |   |   |             |
| Reduction Project   |    |          |          |   |   |   |             |
| (0704-0188),        |    |          |          |   |   |   |             |
| Washington, DC      |    |          |          |   |   |   |             |
| 20503.              |    |          |          |   |   |   |             |
+---------------------+----+----------+----------+---+---+---+-------------+
| 1\. AGENCY USE ONLY |    | 2\.      |          | 3 |   |   |             |
|                     |    | REPORT   |          | \ |   |   |             |
|                     |    | DATE     |          | . |   |   |             |
|                     |    | August   |          | R |   |   |             |
|                     |    | 2003     |          | E |   |   |             |
|                     |    |          |          | P |   |   |             |
|                     |    |          |          | O |   |   |             |
|                     |    |          |          | R |   |   |             |
|                     |    |          |          | T |   |   |             |
|                     |    |          |          | T |   |   |             |
|                     |    |          |          | Y |   |   |             |
|                     |    |          |          | P |   |   |             |
|                     |    |          |          | E |   |   |             |
|                     |    |          |          | A |   |   |             |
|                     |    |          |          | N |   |   |             |
|                     |    |          |          | D |   |   |             |
|                     |    |          |          | D |   |   |             |
|                     |    |          |          | A |   |   |             |
|                     |    |          |          | T |   |   |             |
|                     |    |          |          | E |   |   |             |
|                     |    |          |          | S |   |   |             |
|                     |    |          |          | C |   |   |             |
|                     |    |          |          | O |   |   |             |
|                     |    |          |          | V |   |   |             |
|                     |    |          |          | E |   |   |             |
|                     |    |          |          | R |   |   |             |
|                     |    |          |          | E |   |   |             |
|                     |    |          |          | D |   |   |             |
|                     |    |          |          | F |   |   |             |
|                     |    |          |          | i |   |   |             |
|                     |    |          |          | n |   |   |             |
|                     |    |          |          | a |   |   |             |
|                     |    |          |          | l |   |   |             |
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|                     |    |          |          | e |   |   |             |
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|                     |    |          |          | D |   |   |             |
|                     |    |          |          | e |   |   |             |
|                     |    |          |          | c |   |   |             |
|                     |    |          |          | e |   |   |             |
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|                     |    |          |          | 9 |   |   |             |
|                     |    |          |          | - |   |   |             |
|                     |    |          |          | - |   |   |             |
|                     |    |          |          | D |   |   |             |
|                     |    |          |          | e |   |   |             |
|                     |    |          |          | c |   |   |             |
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|                     |    |          |          | 2 |   |   |             |
+---------------------+----+----------+----------+---+---+---+-------------+
| 4\. TITLE AND       |    |          |          |   | 5 |   |             |
| SUBTITLE            |    |          |          |   | \ |   |             |
| Development of      |    |          |          |   | . |   |             |
| Requirement         |    |          |          |   | F |   |             |
| Specifications for  |    |          |          |   | U |   |             |
| Transit Frontal     |    |          |          |   | N |   |             |
| Collision Warning   |    |          |          |   | D |   |             |
| System              |    |          |          |   | I |   |             |
|                     |    |          |          |   | N |   |             |
|                     |    |          |          |   | G |   |             |
|                     |    |          |          |   | N |   |             |
|                     |    |          |          |   | U |   |             |
|                     |    |          |          |   | M |   |             |
|                     |    |          |          |   | B |   |             |
|                     |    |          |          |   | E |   |             |
|                     |    |          |          |   | R |   |             |
|                     |    |          |          |   | S |   |             |
+---------------------+----+----------+----------+---+---+---+-------------+
| 6\. AUTHOR(S) Xiqin |    |          |          |   |   |   |             |
| Wang, Joanne Chang, |    |          |          |   |   |   |             |
| Ching-Yao Chan,     |    |          |          |   |   |   |             |
| Scott Johnston, Kun |    |          |          |   |   |   |             |
| Zhou, Aaron         |    |          |          |   |   |   |             |
| Steinfeld, Matt     |    |          |          |   |   |   |             |
| Hanson, and Wei-Bin |    |          |          |   |   |   |             |
| Zhang               |    |          |          |   |   |   |             |
+---------------------+----+----------+----------+---+---+---+-------------+
| 7\. PERFORMING      |    |          |          |   | 8 |   |             |
| ORGANIZATION        |    |          |          |   | \ |   |             |
| NAME(S) AND         |    |          |          |   | . |   |             |
| ADDRESS(ES)         |    |          |          |   | P |   |             |
| California PATH     |    |          |          |   | E |   |             |
| Program, Institute  |    |          |          |   | R |   |             |
| of Transportation   |    |          |          |   | F |   |             |
| Studies, University |    |          |          |   | O |   |             |
| of California,      |    |          |          |   | R |   |             |
| Berkeley, Richmond  |    |          |          |   | M |   |             |
| Field Station, 1357 |    |          |          |   | I |   |             |
| South 46^th^        |    |          |          |   | N |   |             |
| Street, Bldg. 452,  |    |          |          |   | G |   |             |
| Richmond, CA        |    |          |          |   | O |   |             |
| 94804-4648          |    |          |          |   | R |   |             |
|                     |    |          |          |   | G |   |             |
|                     |    |          |          |   | A |   |             |
|                     |    |          |          |   | N |   |             |
|                     |    |          |          |   | I |   |             |
|                     |    |          |          |   | Z |   |             |
|                     |    |          |          |   | A |   |             |
|                     |    |          |          |   | T |   |             |
|                     |    |          |          |   | I |   |             |
|                     |    |          |          |   | O |   |             |
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|                     |    |          |          |   | O |   |             |
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|                     |    |          |          |   | T |   |             |
|                     |    |          |          |   | N |   |             |
|                     |    |          |          |   | U |   |             |
|                     |    |          |          |   | M |   |             |
|                     |    |          |          |   | B |   |             |
|                     |    |          |          |   | E |   |             |
|                     |    |          |          |   | R |   |             |
|                     |    |          |          |   | U |   |             |
|                     |    |          |          |   | C |   |             |
|                     |    |          |          |   | B |   |             |
|                     |    |          |          |   | - |   |             |
|                     |    |          |          |   | I |   |             |
|                     |    |          |          |   | T |   |             |
|                     |    |          |          |   | S |   |             |
|                     |    |          |          |   | - |   |             |
|                     |    |          |          |   | P |   |             |
|                     |    |          |          |   | R |   |             |
|                     |    |          |          |   | R |   |             |
|                     |    |          |          |   | - |   |             |
|                     |    |          |          |   | 2 |   |             |
|                     |    |          |          |   | 0 |   |             |
|                     |    |          |          |   | 0 |   |             |
|                     |    |          |          |   | 4 |   |             |
|                     |    |          |          |   | - |   |             |
|                     |    |          |          |   | 1 |   |             |
|                     |    |          |          |   | 4 |   |             |
+---------------------+----+----------+----------+---+---+---+-------------+
| 9\.                 |    |          |          |   | 1 |   |             |
| SP                  |    |          |          |   | 0 |   |             |
| ONSORING/MONITORING |    |          |          |   | \ |   |             |
| AGENCY NAME(S) AND  |    |          |          |   | . |   |             |
| ADDRESS(ES)         |    |          |          |   | S |   |             |
|                     |    |          |          |   | P |   |             |
| ### Federal Tra     |    |          |          |   | O |   |             |
| nsit Administration |    |          |          |   | N |   |             |
|                     |    |          |          |   | S |   |             |
| U.S. Department of  |    |          |          |   | O |   |             |
| Transportation      |    |          |          |   | R |   |             |
|                     |    |          |          |   | I |   |             |
| Washington, DC      |    |          |          |   | N |   |             |
| 20590 Website URL   |    |          |          |   | G |   |             |
| \[www.fta.dot.gov\] |    |          |          |   | / |   |             |
|                     |    |          |          |   | M |   |             |
|                     |    |          |          |   | O |   |             |
|                     |    |          |          |   | N |   |             |
|                     |    |          |          |   | I |   |             |
|                     |    |          |          |   | T |   |             |
|                     |    |          |          |   | O |   |             |
|                     |    |          |          |   | R |   |             |
|                     |    |          |          |   | I |   |             |
|                     |    |          |          |   | N |   |             |
|                     |    |          |          |   | G |   |             |
|                     |    |          |          |   | \ |   |             |
|                     |    |          |          |   | A |   |             |
|                     |    |          |          |   | G |   |             |
|                     |    |          |          |   | E |   |             |
|                     |    |          |          |   | N |   |             |
|                     |    |          |          |   | C |   |             |
|                     |    |          |          |   | Y |   |             |
|                     |    |          |          |   | R |   |             |
|                     |    |          |          |   | E |   |             |
|                     |    |          |          |   | P |   |             |
|                     |    |          |          |   | O |   |             |
|                     |    |          |          |   | R |   |             |
|                     |    |          |          |   | T |   |             |
|                     |    |          |          |   | N |   |             |
|                     |    |          |          |   | U |   |             |
|                     |    |          |          |   | M |   |             |
|                     |    |          |          |   | B |   |             |
|                     |    |          |          |   | E |   |             |
|                     |    |          |          |   | R |   |             |
|                     |    |          |          |   |   |   |             |
|                     |    |          |          |   | F |   |             |
|                     |    |          |          |   | T |   |             |
|                     |    |          |          |   | A |   |             |
|                     |    |          |          |   | - |   |             |
|                     |    |          |          |   | T |   |             |
|                     |    |          |          |   | R |   |             |
|                     |    |          |          |   | I |   |             |
|                     |    |          |          |   | - |   |             |
|                     |    |          |          |   | 0 |   |             |
|                     |    |          |          |   | 5 |   |             |
|                     |    |          |          |   | . |   |             |
|                     |    |          |          |   | 2 |   |             |
+---------------------+----+----------+----------+---+---+---+-------------+
| 11. Supplementary   |    |          |          |   |   |   |             |
|     Notes.          |    |          |          |   |   |   |             |
+---------------------+----+----------+----------+---+---+---+-------------+
| 12a.                |    |          |          |   |   | 1 |             |
| DISTRI              |    |          |          |   |   | 2 |             |
| BUTION/AVAILABILITY |    |          |          |   |   | b |             |
| STATEMENT           |    |          |          |   |   | . |             |
|                     |    |          |          |   |   | D |             |
| **Available From:** |    |          |          |   |   | I |             |
| National Technical  |    |          |          |   |   | S |             |
| Information         |    |          |          |   |   | T |             |
| Service/NTIS, 5285  |    |          |          |   |   | R |             |
| Port Royal Road,    |    |          |          |   |   | I |             |
| Springfield,        |    |          |          |   |   | B |             |
| Virginia, 22161.    |    |          |          |   |   | U |             |
| Phone 703.605.6000, |    |          |          |   |   | T |             |
| Fax 703.605.6900,   |    |          |          |   |   | I |             |
| Email               |    |          |          |   |   | O |             |
| \[orders@           |    |          |          |   |   | N |             |
| ntis.fedworld.gov\] |    |          |          |   |   | C |             |
|                     |    |          |          |   |   | O |             |
|                     |    |          |          |   |   | D |             |
|                     |    |          |          |   |   | E |             |
+---------------------+----+----------+----------+---+---+---+-------------+
| 12. ABSTRACT This   |    |          |          |   |   |   |             |
|     report          |    |          |          |   |   |   |             |
|     documents the   |    |          |          |   |   |   |             |
|     development of  |    |          |          |   |   |   |             |
|     a preliminary   |    |          |          |   |   |   |             |
|     specification   |    |          |          |   |   |   |             |
|     for a transit   |    |          |          |   |   |   |             |
|     bus frontal     |    |          |          |   |   |   |             |
|     collision       |    |          |          |   |   |   |             |
|     warning system, |    |          |          |   |   |   |             |
|     based on a      |    |          |          |   |   |   |             |
|     system          |    |          |          |   |   |   |             |
|     engineering     |    |          |          |   |   |   |             |
|     approach. The   |    |          |          |   |   |   |             |
|     research        |    |          |          |   |   |   |             |
|     efforts         |    |          |          |   |   |   |             |
|     included: 1) a  |    |          |          |   |   |   |             |
|     literature      |    |          |          |   |   |   |             |
|     review, 2)      |    |          |          |   |   |   |             |
|     detailed        |    |          |          |   |   |   |             |
|     analyses of the |    |          |          |   |   |   |             |
|     five-year       |    |          |          |   |   |   |             |
|     safety records  |    |          |          |   |   |   |             |
|     of a group of   |    |          |          |   |   |   |             |
|     California      |    |          |          |   |   |   |             |
|     transit         |    |          |          |   |   |   |             |
|     properties to   |    |          |          |   |   |   |             |
|     identify the    |    |          |          |   |   |   |             |
|     causes of their |    |          |          |   |   |   |             |
|     safety          |    |          |          |   |   |   |             |
|     problems, 3) an |    |          |          |   |   |   |             |
|     in-depth data   |    |          |          |   |   |   |             |
|     collection and  |    |          |          |   |   |   |             |
|     analysis from   |    |          |          |   |   |   |             |
|     instrumented    |    |          |          |   |   |   |             |
|     buses serving   |    |          |          |   |   |   |             |
|     San Mateo       |    |          |          |   |   |   |             |
|     County, CA,     |    |          |          |   |   |   |             |
|     and 4)          |    |          |          |   |   |   |             |
|     development and |    |          |          |   |   |   |             |
|     testing of      |    |          |          |   |   |   |             |
|     three           |    |          |          |   |   |   |             |
|     generations of  |    |          |          |   |   |   |             |
|     transit bus     |    |          |          |   |   |   |             |
|     frontal         |    |          |          |   |   |   |             |
|     collision       |    |          |          |   |   |   |             |
|     warning         |    |          |          |   |   |   |             |
|     systems,        |    |          |          |   |   |   |             |
|     incorporating   |    |          |          |   |   |   |             |
|     enhancements to |    |          |          |   |   |   |             |
|     meet the needs  |    |          |          |   |   |   |             |
|     identified by   |    |          |          |   |   |   |             |
|     the bus drivers |    |          |          |   |   |   |             |
|     using the       |    |          |          |   |   |   |             |
|     prototype       |    |          |          |   |   |   |             |
|     systems. The    |    |          |          |   |   |   |             |
|     analyses of the |    |          |          |   |   |   |             |
|     safety records  |    |          |          |   |   |   |             |
|     and the         |    |          |          |   |   |   |             |
|     combination of  |    |          |          |   |   |   |             |
|     video and       |    |          |          |   |   |   |             |
|     engineering     |    |          |          |   |   |   |             |
|     data from the   |    |          |          |   |   |   |             |
|     instrumented    |    |          |          |   |   |   |             |
|     buses provide a |    |          |          |   |   |   |             |
|     uniquely rich   |    |          |          |   |   |   |             |
|     pool of data    |    |          |          |   |   |   |             |
|     for diagnosing  |    |          |          |   |   |   |             |
|     transit bus     |    |          |          |   |   |   |             |
|     safety          |    |          |          |   |   |   |             |
|     challenges. The |    |          |          |   |   |   |             |
|     prototype       |    |          |          |   |   |   |             |
|     warning systems |    |          |          |   |   |   |             |
|     incorporated    |    |          |          |   |   |   |             |
|     innovations in  |    |          |          |   |   |   |             |
|     signal          |    |          |          |   |   |   |             |
|     processing to   |    |          |          |   |   |   |             |
|     ensure that     |    |          |          |   |   |   |             |
|     warnings are    |    |          |          |   |   |   |             |
|     issued with     |    |          |          |   |   |   |             |
|     high            |    |          |          |   |   |   |             |
|     reliability and |    |          |          |   |   |   |             |
|     low rates of    |    |          |          |   |   |   |             |
|     false alerts.   |    |          |          |   |   |   |             |
|     Finally, the    |    |          |          |   |   |   |             |
|     results of this |    |          |          |   |   |   |             |
|     work led to the |    |          |          |   |   |   |             |
|     definition of a |    |          |          |   |   |   |             |
|     preliminary     |    |          |          |   |   |   |             |
|     specification   |    |          |          |   |   |   |             |
|     for a frontal   |    |          |          |   |   |   |             |
|     collision       |    |          |          |   |   |   |             |
|     warning system  |    |          |          |   |   |   |             |
|     for subsequent  |    |          |          |   |   |   |             |
|     field testing.  |    |          |          |   |   |   |             |
+---------------------+----+----------+----------+---+---+---+-------------+
| 14\. SUBJECT TERMS  |    |          |          |   |   |   | 15\. NUMBER |
| Forward collision   |    |          |          |   |   |   | OF PAGES    |
| warning, collision  |    |          |          |   |   |   | 181         |
| warning, urban      |    |          |          |   |   |   |             |
| transit, human      |    |          |          |   |   |   |             |
| factors, collision  |    |          |          |   |   |   |             |
| avoidance, crash    |    |          |          |   |   |   |             |
| avoidance.          |    |          |          |   |   |   |             |
+---------------------+----+----------+----------+---+---+---+-------------+
|                     |    |          |          |   |   |   | 16\. PRICE  |
|                     |    |          |          |   |   |   | CODE        |
+---------------------+----+----------+----------+---+---+---+-------------+
| 17\. SECURITY       | 18 |          | 19\.     |   |   |   | 20\.        |
| CLASSIFICATION\     | \. |          | SECURITY |   |   |   | LIMITATION  |
| OF REPORT           | SE |          | CLASSIF  |   |   |   | OF ABSTRACT |
|                     | CU |          | ICATION\ |   |   |   |             |
| Unclassified        | RI |          | OF       |   |   |   |             |
|                     | TY |          | ABSTRACT |   |   |   |             |
|                     | C  |          |          |   |   |   |             |
|                     | LA |          | Uncl     |   |   |   |             |
|                     | SS |          | assified |   |   |   |             |
|                     | IF |          |          |   |   |   |             |
|                     | IC |          |          |   |   |   |             |
|                     | AT |          |          |   |   |   |             |
|                     | IO |          |          |   |   |   |             |
|                     | N\ |          |          |   |   |   |             |
|                     | OF |          |          |   |   |   |             |
|                     | TH |          |          |   |   |   |             |
|                     | IS |          |          |   |   |   |             |
|                     | PA |          |          |   |   |   |             |
|                     | GE |          |          |   |   |   |             |
|                     |    |          |          |   |   |   |             |
|                     | Un |          |          |   |   |   |             |
|                     | cl |          |          |   |   |   |             |
|                     | as |          |          |   |   |   |             |
|                     | si |          |          |   |   |   |             |
|                     | fi |          |          |   |   |   |             |
|                     | ed |          |          |   |   |   |             |
+---------------------+----+----------+----------+---+---+---+-------------+

## *DISCLAIMER NOTICE*

This document is disseminated under the sponsorship of the U.S.
Department of Transportation in the interest of information exchange.
The United States Government assumes no liability for its contents or
use thereof.

The United States Government does not endorse products of manufacturers.
Trade or manufacturers' names appear herein solely because they are
considered essential to the objective of this report.

![](media/image1.png){width="1.0104166666666667in" height="1.03125in"}

![](media/image2.png){width="1.7604166666666667in"
height="1.3645833333333333in"}

  ----------------------------------- -----------------------------------
  **PROJECT No.**                     **COPY No. \_\_\_\_\_**

  ----------------------------------- -----------------------------------

Development of Requirement Specifications for Transit Frontal Collision
Warning System

**Final Report**

Xiqin Wang, Joanne Chang, Ching-Yao Chan, Scott Johnston, Kun Zhou,

Aaron Steinfeld[^1], Matt Hanson, and Wei-Bin Zhang

California PATH Program

University of California, Berkeley

in collaboration with

Federal Transit Administration

San Mateo Transit District

California Department of Transportation

and

Gillig Company

August 2003

  ---------------------------------------------------- ---------------------------------------------------- ---------------------------------------------------- ----------------------------------------------------
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TABLE OF CONTENTS

Page

EXECUTIVE SUMMARY x

INTRODUCTION 1

BACKGROUND 4

**SECTION ONE**: **UNDERSTANDING TRANSIT FRONTAL COLLISIONS** 9

> 1\. ACCIDENT DATA ANALYSIS 10
>
> 2\. FIELD DATA ANALYSIS 41

**SECTION TWO: DEVELOPMENT OF PROTOTYPE\
TRANSIT FRONTAL COLLISION WARNING SYSTEMS** 64

> 3\. DEVELOPMENT OF A PROTOTYPE TRANSIT FCWS 65
>
> 4\. DESIGN OF THE FCWS DRIVER VEHICLE INTERFACE (DVI) 92

**SECTION THREE: DEVELOPMENT OF\
PRELIMINARY SPECIFICATIONS** 115

> 5\. DEVELOPMENT OF PRELIMINARY SPECIFICATIONS 116
>
> 6\. TRANSIT BUS FRONTAL COLLISION-WARNING\
> SYSTEMS: PRELIMINARY PERFORMANCE SPECIFICATIONS 123
>
> 7\. SUMMARY 132
>
> 8\. APPENDIX 135
>
> APPENDIX I: List of 32-CALTIP Members 136
>
> APPENDIX II: Sample JGAA Cost Report 137
>
> APPENDIX III: Loss Code Description 138
>
> APPENDIX IV: Accident Data as shown in Bar Charts 140
>
> APPENDIX V: Development of Data Acquisition System (DAS) 142
>
> APPENDIX VI: Suggestions on other Display Modalities 162
>
> APPENDIX VII: FCWS Survey Questions 164
>
> APPENDIX VIII: FCWS Evaluation Questionnaire 165

LIST OF FIGURES

Page

Figure 1. Typical bus x

Figure 2. Frontal collision warning system functions 3

Figure 3. Service coverage of 35 transit agencies 12

Figure 4. Agency I: Accident costs by accident type 14

Figure 5. Agency I: Collision accident costs by initial point of impact
14

Figure 6. Agency II: Accident costs by accident type 15

Figure 7. Agency II: Collision accident costs by initial point of impact
15

Figure 8. Agency III: Accident costs by accident type 16

Figure 9. Agency III: Collision accident costs by initial point of
impact 16

Figure 10. Agency IV: Accident costs by accident type 17

Figure 11. Agency IV: Collision accident costs by initial point of
impact 17

Figure 12. Claim and cost distributions for collision accidents costing
less then 10K 19

Figure 13. Claim and cost distributions for all collision accidents 19

Figure 14. Agency V: Accident costs by accident type 20

Figure 15. Agency V: Accident costs by initial point of impact 20

Figure 16. 30-CalTIP members: Accident costs by accident type 21

Figure 17. 30-CalTIP members: Collision accident costs by initial point
of impact 21

Figure 18. 35-transit agencies: General collision accident costs by
initial point of impact 24

Figure 19. 35-transit agencies: Cost per claim by initial point of
impact 25

Figure 20. 35-transit agencies: General collisions by fiscal year 26

Figure 21. 35-transit agencies: General collisions by fiscal year and
initial point of impact 26

Figure 22. 35-transit agencies: General collision accident costs by
collision object 27

Figure 23. 35-transit agencies: General vehicle collision accident costs
by accident scenario 28

Figure 24. 35-transit agencies: Five collision scenarios by fiscal year
29

Figure 25. 35-transit agencies: Five collision scenarios 29

Figure 26. 35-transit agencies: General passenger injuries by fiscal yea
31

Figure 27. 35-transit agencies: Passenger injuries by bus maneuver 32

Figure 28. 35-transit agencies: Passenger injuries on stopping bus among
all general injuries 32

Figure 29. Number of accidents and traffic volume vs. hour 37

Figure 30. Number of accidents and traffic volume vs. hour 37

Figure 31. Sensor arrangements of the Data Acquisition System Schematic
41

Figure 32. Diagram of the data acquisition system 42

Figure 33. Snapshot of the data playback tool window 43

Figure 34. Relative frequency distribution of bus speed when bus is
moving 46

Figure 35. Percentage of time for bus speed 47

Figure 36. Relative frequency distribution of bus acceleration when bus
is moving 48

Figure 37. Percentage of time for bus acceleration 49

Figure 38. Percentage of time for no-brake vs. brake 50

Figure 39. Relative frequency distribution of brake pressure 51

Figure 40. Percentage of time for brake with different pressure levels
51

Figure 41. Relative frequency distribution of front wheel angle
(+left/-right) 52

Figure 42. Relative frequency distribution of minimum following distance
53

Figure 43. Relative frequency distribution of closing rate 54

**LIST OF FIGURES (cont.)**

Page

Figure 44. Percentage of time for closing rate 55

Figure 45. Bus speed histogram 56

Figure 46. Onset brake pressure histogram 57

Figure 47. Target range histogram 57

Figure 48. Target speed histogram 58

Figure 49. Time to-collision histogram 59

Figure 50. Bus speed histogram 60

Figure 51. *Vt*-to-*Vb* ratio histogram 61

Figure 52. Clusters of target following scenarios 62

Figure 53. JDL data fusion process model 66

Figure 54. Bus collision-warning algorithm architecture 69

Figure 55. Algorithm framework 70

Figure 56. Tracking algorithm diagram 71

Figure 57. Multiple target tracking result 73

Figure 58. Multiple target trajectories 73

Figure 59. Display of the preliminary algorithm in Windows™ environment
77

Figure 60. Trajectories of objects in radar's coordinate system 78

Figure 61. Trajectories of objects (blue) and the bus (red) in the
inertial system 79

Figure 62. Clustering of braking onset timing 80

Figure 63. Track file structure 81

Figure 64. ID queue structure 82

Figure 65. Object state buffer structure 82

Figure 66. Vehicle kinematic model 85

Figure 67. Vehicle state model 85

Figure 68. Coordinate transformation 87

Figure 69. Preliminary DVI design 99

Figure 70. Simulated FCWS DVI 101

Figure 71. Spatial coverage illustration 118

Figure 72. Spatial coverage illustration 127

Figure 73. Sensors installed on a bus 143

Figure 74. System layout on the bus 144

Figure 75. FCS and front sensors 146

Figure 76. RCS and rear sensors 147

Figure 77. LIDAR calibration geometry 148

Figure 78. Control point images 152

Figure 79. δy of four cameras 153

Figure 80. δx of four cameras 154

Figure 81. Object locations for system alignment 156

Figure 82. PRADAR data for system alignment 157

Figure 83. DRADAR data for system alignment 157

Figure 84. LIDAR data for system alignment 158

Figure 85. Object locations reported by sensors 158

LIST OF TABLES

Page

Table 1: Buses involved in all crashes by the initial point of impact 10

Table 2: Accident cost data for 35-transit agencies (for 5 years) 13

Table 3: Collision accident cost data for 35-transit agencies (5 years)
22

Table 4: Total accident cost data for 35-transit agencies (5 years) 22

Table 5: Serious casualties for 35-transit agencies (5 years) 23

Table 6: List of accident scenarios 27

Table 7: Severe passenger injuries for 35-transit agencies (5 years) 30

Table 8: Maneuver types prior to an accident 31

Table 9: Accident costs 1997 dollars in California comprehensive cost
method 35

Table 10: Accidents Involving Buses on California State Highways
1996--1998 36

Table 11: Cost Estimates of Accidents Involving Buses 1996--1998 36

Table 12: Categories of bus speed 60

Table 13: Categories of speed ratio 61

Table 14: Total numbers of cases in each cluster 62

Table 15: JDL process model components summary 66

Table 16: Distance matrix 84

Table 17: Operator comments on the current physical operating
environment 93

Table 18: Operator requirements of a FCWS 94

Table 19: Operators comment of when a FCWS would be most helpful 95

Table 20: Operator suggestions for design of the warning 96

Table 21: Operator comments on visual warnings 97

Table 22: Top down illumination method 101

Table 23: Looming illumination method 102

Table 24: Operator Feedback of FCWS System 106

Table 25: Operator ratings sheet of the visual DVI 110

Table 26: Claim and cost distributions for collision accidents with cost
less then 10K 140

Table 27: Claim and cost distributions for all collision accidents 140

Table 28: Transit agencies: General collision accident costs by initial
point of impact 140

Table 29: Transit agencies: General collision accident costs by
collision object 141

Table 30: Transit agencies: General vehicle collision costs by accident
scenario 141

Table 31: Transit agencies: Passenger injuries by bus movements 141

Table 32: DAS calibration abbreviations 145

Table 33: Front sensor locations 146

Table 34: Rear sensor locations 147

Table 35: LIDAR lateral position test 148

Table 36: LIDAR range test 148

Table 37: LIDAR vertical position test 149

Table 38: Focal length of cameras 149

Table 39: Parameter table 151

Table 40: Intrinsic and extrinsic parameters 155

Table 41: Derived parameters 156

Table 42: Object locations reported by sensors 159

Table 43: Host vehicle parameter biased values 160

Table 44: Accelerometer sensitivity 161

LIST OF TABLES (cont.)

Page

Table 45: Audible warnings feedback from operators and trainers 162

Table 46: Tactile warnings feedback from operators and trainers 162

Table 47: Vehicle control feedback from operators and trainers 163

ACKNOWLEDGMENTS

This project was sponsored by the U.S. Department of Transportation,
Federal Transit Administration (FTA) under the National Intelligent
Vehicle Initiative Program. This report was prepared in cooperation with
the State of California, Business Transportation and Housing Agency,
Department of Transportation. The contents of this report reflect the
views of the authors, who are responsible for the facts and the accuracy
of the data presented herein. The contents do not necessarily reflect
the official views or policies of the State of California or the Federal
Transit Administration. This report does not constitute a standard,
specification, or regulation.

The project team would like to thank Denso Co. for its contribution and
costshare of the lidars used for the prototype collision warning system.
The authors of this report would also like to express our appreciation
to Brian Cronin of FTA for his guidance and support, Alan Lochlead

Dave Nelson, Paul Kretz, Dan Empey, Bart Duncil, Thang Lian, Mark
Miller, Doug Cooper, Steven Shladover and Yongquan Zhang of PATH, Sonja
Sun and Ron Deleon of Caltrans, Chuck Harvey, Jerie Moeller and James
Castagno of SamTrans and Gail Ewing and Brian Macloed of Gillig for
their technical assistance and support, and the Advisory Committee
members for their active participation of the project.

Executive Summary

![](media/image7.jpeg){width="2.5in" height="2.4319444444444445in"}Bus
transit systems need to use all the tools at their disposal to enhance
the public perception of the desirability of their service, including
its safety. Although bus transit is already a very safe mode of travel,
more can be done to help bus drivers avoid crashes and the near-misses
that may require them to brake suddenly. This project has explored how
ITS technologies can be used to help avoid frontal collisions
(collisions with other vehicles or objects located ahead of the bus).
The project has followed a system engineering approach, beginning with a
definition of the problem, preliminary identification of the
requirements, preliminary design, testing and evaluation, and then
several iterations of redesign and re-evaluation to refine the system
and to lead toward the definition of a system specification.

The safety challenges posed by frontal crashes have been defined first,
based on a literature review, analysis of the safety records of a group
of California transit properties, and then an extensive program of data
collection on buses serving San Mateo County, CA. Based on the knowledge
gained from this information, three generations of frontal collision
warning systems have been developed and tested in daily use by bus
drivers, with refinements to the designs incorporated at each generation
based on the reactions of the drivers. Finally, the results of this work
led to the definition of a preliminary specification for a frontal
collision warning system to be field tested in wider use.

Fig. 1 Typical bus

This project was sponsored by the U.S. Department of Transportation,
Federal Transit Administration (FTA), under the Intelligent Vehicle
Initiative (IVI) Program. The U.S. DOT selected a
public/private/academic partnership of industry specialists and
researchers to define the most effective means of mitigating frontal
collisions. The team includes the San Mateo County Transit District
(SamTrans), University of California PATH Program (PATH), California
Department of Transportation (Caltrans) and Gillig Corporation. Most of
the transit agencies in the San Francisco Bay Area are also
participating in the project at an advisory level and have provided
significant inputs to the project.

Crash Data Analyses

The national statistics (from the NHTSA GES database) indicate that the
initial point of impact for 28% of bus crashes is frontal, and therefore
these should be susceptible to mitigation using a frontal collision
warning system. More detailed data are available from the insurance
records of the individual transit properties, and for this project the
relevant data from 35 California transit properties (including three
large ones in the San Francisco Bay Area) were analyzed in greater
depth. Over a five-year period, these agencies experienced 5255 crashes,
of which 31 were classified "serious" (costing over \$100 K), for a
total cost of over \$22 million (more than half of which was
attributable to the small number of serious crashes). Among the 31
serious crashes, eleven were for "bus hitting pedestrian" and nine were
for "bus rear-ending another vehicle". Among the 23 "severe passenger
injury" incidents, costing a total of about \$4.4 million over five
years, one quarter of the events and the costs were because "passenger
fell due to abrupt stop". Of the bus crashes that involved serious
casualties, 55% were frontal collisions, and about half of the collision
costs were also for frontal collisions. So, although the frontal crashes
involving buses are not dominant in their frequency of occurrence, they
are dominant in their severity.

The crash data were augmented with advice provided by the project
advisory committee of representatives from most of the major transit
properties in and around the Bay Area. They helped confirm the
importance of some of the observations derived from the crash data:

-   Most of the crashes occurred at speeds below 30 mph;

-   The crashes are typically in complex urban and suburban driving
    environments with heavy traffic, pedestrians, bicyclists and parked
    vehicles, rather than in the more open highway environment;

-   Many of the incidents occur around the front corners of the bus,
    when it is pulling out from a stop or turning a corner, or when
    another vehicle is moving aggressively ahead of the bus;

-   It is not only important to avoid crashes, but it is also important
    to help the driver react early to threats in order to avoid hard
    braking events that cause standing passengers to fall and injure
    themselves, even if an impact with another vehicle is avoided.

These aspects of the transit bus operations indicate the unsuitability
of the commercially available collision warning systems for this
application. Those systems are designed for use in the highway
environment, where the patterns of movement of the equipped vehicle and
the surrounding vehicles are much simpler and do not change as rapidly.

Field Data Collection and Analysis

In order to design a collision warning system that bus drivers must use
every day, not just in the rare emergency condition, it is necessary to
have an accurate characterization of their driving environment. Samtrans
buses operate under a very diverse set of conditions, ranging from the
highest urban densities of downtown San Francisco to suburban commercial
and residential arterials, rural roads and high-speed suburban freeways.
In order to develop a solid quantitative characterization of these
operating conditions, three Samtrans buses were equipped with sensors
and data acquisition systems. These included video cameras looking ahead
on both sides of the bus, together with forward-looking laser and
millimeter-wave radar and sonar sensors to measure the distances and
closing rates to objects that could represent hazards to the bus, plus
internal sensors to record engineering data about the bus location,
speed, accelerations and driver actions (steering, braking, etc.).

The recorded video data enabled the analysts to understand the
environmental conditions associated with the data acquired from the
other sensors. This also made it possible to determine the effectiveness
of those sensors in detecting different types of potential hazards, when
the sensor outputs were examined in conjunction with the video. The
sonar sensors were not found to be useful for frontal collision warning
because of their severely limited range. The laser and millimeter wave
radars that were tested had complementary characteristics based on their
specific designs, but these are not necessarily inherent attributes of
other sensors using these respective technologies. The laser radar
provided a wider field of view, with good azimuth angle resolution and
accurate target range data, but no information about range rate (closing
speed). The millimeter wave radar relied on the Doppler effect, which
provided it with good range and range rate capabilities when the targets
were moving at a significant speed relative to the bus, but led to a
loss of target at low relative speed. The millimeter wave radar had a
narrower field of view and poorer azimuth angle resolution, but was less
vulnerable to degraded performance in wet weather conditions.

The recorded engineering data provided the basis for characterizing the
statistical distributions of operating speed and acceleration of the
buses, as well as other features such as the distribution of brake use
at different levels of brake pressure, and minimum following distances
and closing rates to other vehicles. These data taken individually do
not necessarily reveal much about safety considerations, but when they
are combined they can be more useful. For example, these data made it
possible to define the distribution of bus speed at the time the driver
first applies the brakes, showing that most brake initiations are at
speeds between 9 and 27 mph. The data also show clearly that the level
of brake pressure at the onset of braking is very heavily weighted
toward small values, indicating that the large majority of braking is
smooth rather than abrupt.

The forward ranging sensor data provide useful statistical information
about the range and closing speed to forward targets at the initiation
of braking. The probability distribution of forward target range at the
time of brake application is broad, with a peak at about 30 m and
relatively smooth slopes from zero at the short end to maximum sensor
range at the long end. The distribution of time-to-collision to the
closest target at the onset of braking shows a peak at about 6 seconds,
with smooth slopes away from that on both sides, but very few samples
below 2 seconds. This needs to be treated cautiously because the targets
that were measured here may not have been the direct reasons for the
braking to occur (not in the lane of travel, etc.). When the
distribution of the ratio of the speed of the target to the speed of the
bus at the onset of braking is plotted, there are two peaks, at ratios
of 0.04 and 0.9. This indicates that most of the targets the driver is
trying to avoid are either very slow (stationary) or moving at a speed
similar to that of the bus. Cross-plotting this ratio with the bus speed
for all braking events provides a visual indication of the kinds of
circumstances in which the driver is more or less likely to find the
need to apply the brakes.

Prototype Forward Collision-Warning System Design and Evaluation

Based on the knowledge of the transit bus driving and crash hazard
environment, prototype forward collision warning systems were designed,
developed and tested in use by Samtrans drivers. The primary sensor for
the prototype warning system was the laser radar (lidar), based on its
wider field of view and accurate range measurements, while the
measurements from the other sensors were recorded for later analysis and
evaluation. The key challenge in the design of the warning system, as
with most such systems, was in setting the warning threshold low enough
to issue alerts under all serious hazard conditions without making it so
low that it would issue too many false or nuisance alerts (when the
driver would not consider the alert to be appropriate). If the nuisance
alert rate is too high, the driver will dislike the system and will come
to disregard its alerts, even when they may indeed be valid.

All of the warning algorithms had to build on a foundation of strong
signal processing to identify and track targets from the raw radar data.
Once the targets were identified and tracked, several approaches were
applied to decide when to issue warnings to the drivers. The first
approach used linear prediction to estimate the time to collision (TTC)
between the bus and the targets. This was not well accepted by the
drivers because it tended to generate too many false positives,
primarily associated with objects to the side of the vehicle's travel
path (parked cars, guard rails) and with yaw motions of the bus.

The problem with the yaw motions was greatly reduced in the second
iteration of the warning algorithm design by using a coordinate
transformation, based on compensating for the yaw rotation of the
vehicle, to express all target measurements in an inertial reference
frame rather than the vehicle's (rotating) reference frame. This greatly
simplified the analysis needed to assess the threats posed by each of
the targets, so that attention could be focused on the targets that were
really in the path of the vehicle. The result was the elimination of
most of the false positives that occurred while the bus was turning.

The third iteration of the warning algorithm further reduced the
nuisance alert level by changing from a TTC warning criterion to a
criterion defined based on the rate of braking the driver would need to
apply to avoid hitting the target. The naturalistic driving data
collected from the Samtrans bus drivers was used to define the braking
onsets in the phase plane of range and range rate measurements. This
scatter plot showed dramatic clustering of braking onsets, indicating a
well-defined boundary of combinations of range and range rate at which
the large majority of drivers would apply the brakes. This boundary, as
an empirical representation of the braking preferences of the drivers,
provides an excellent way of specifying the warning frontier to minimize
nuisance alerts, and the drivers who have tested-driven the warning
systems based on it have generally accepted it.

The driver-vehicle interface (DVI) is a critical element in the design
of the warning system, and has benefited substantially from continuing
involvement of the Samtrans drivers in the design process. The bus
driving application is very specialized because they are professional
drivers, like truck drivers, but they are also sensitive to the
reactions of the passengers they are serving. Therefore, it is important
to them that the DVI not be so salient that it attracts the attention of
their passengers, when it issues a warning. Also, because of the
importance of avoiding hard braking events that could injure standing
passengers, they need to receive the warnings early enough to be able to
brake at a moderate deceleration rate. The night-time drivers prefer an
audible alert to a visual alert because they are concerned about the
visual distraction of a lighted display in the bus when they are trying
to watch a dark driving scene, but the day-time drivers tend to prefer
the visual alert because it is less likely to draw the attention of
their passengers. Because of the diversity of driving styles, there was
also a significant preference among the drivers for adjustability of the
warning sensitivity and the salience of the DVI alert.

The prototype warning system uses two vertical rows of colored LEDs
installed on the center and left A-pillars of the bus. These are
illuminated in a sequence from yellow to red and from top to bottom as
the urgency of the threat increases. If the threat is primarily to one
side or the other of the bus, the LEDs on the more seriously threatened
side are illuminated, but if it is straight ahead, both LED rows are
illuminated.

The drivers who have used it have generally accepted the warning system
and its DVI, but the sample of drivers and extent of their usage remains
limited. Longer-term test-driving results will be needed to determine
the extent to which their driving behavior is modified based on their
experience with the warning system.

Preliminary Performance Requirement Specification

Based on the knowledge gained from the successive cycles of system
design and evaluation, a preliminary performance requirement
specification has been defined for the frontal collision warning system.
This can serve as the basis for the design of the next generation system
for larger-scale field-testing and evaluation, to lead toward the
development of a system that can eventually be widely deployed on buses
throughout the U.S.

Introduction

The U.S. Department of Transportation (US DOT) initiated the Intelligent
Vehicle Initiative (IVI) Program with the goal of improving safety
through the application of advanced technologies. The frontal collision
warning function has been identified as one of the key safety
improvement measures for the transit vehicle platform of the IVI
Program. Frontal collision, defined as a bus colliding with a vehicle in
front of the bus, is a frequent incident in transit bus operations and
the cause of property damage, personal injuries, and interruption to bus
operations. A team that includes San Mateo County Transit District
(SamTrans), the University of California PATH Program (PATH), California
Department of Transportation (Caltrans), and the Gillig Corporation has
been selected by the US DOT to develop and validate performance and
technical requirement specifications for Frontal Collision Warning
Systems (FCWS) for transit buses. Additionally, a group of local transit
agencies are participating in the project in an advisory level. The
project began in January 2000 with a planned duration of two years.

SamTrans operates a fleet of 316 buses in the counties of San Mateo,
Santa Clara, and San Francisco that covers one of the most congested
areas in the United States. Accident statistics tracked by SamTrans in
recent years indicate frontal collisions can result in significant
property damage and liability. In addition to frontal collisions,
passenger falls resulting from emergency braking also contribute to an
increased potential for passenger injuries and liability. This finding
is further supported by the accident data collected by a number of
transit agencies in the Bay Area (members of FCWS Bay Area Transit
Advisory Committee). The accident data analysis suggests that a FCWS
using advanced sensing and computer technologies can potentially reduce
frontal collision accident rates, which will minimize losses and reduce
operational interruptions. The collision warning system may also help
the driver to adequately respond to the hazard with smoother maneuvers.
Furthermore, information collected through sensors can be recorded for
the purpose of accident analysis and for avoiding false claims.

The ***purpose*** of the transit Frontal Collision Warning System (FCWS)
under the context of this project is to (a) address imminent crashes,
(b) provide warnings for smoother maneuvering, and (c) provide warnings
when a bus is too close to a forward vehicle.

Previous studies on collision warning and collision avoidance have
focused on highway applications, freight trucks, and light-duty
passenger cars. The project team has conducted a literature review and
found no existing work on FCWS for transit buses, the subject of the
current project. The transit bus application environment differs from
existing CWS development efforts mainly in the following two ways. First
of all, most of the transit frontal accidents occurred in urban areas.
The urban and suburban operating environment is dramatically different
from those targeted in previous CWS studies, thus present considerable
challenges with respect to the diversity of obstacles to be detected and
the different traffic patterns. The transit FCWS must be able to deal
with the environment that current CWS deals with as well as in
complicated urban settings. The second major difference is the
driver/passenger population. Transit bus drivers are professional
drivers who may have different needs from and sensitivities to a FCWS.
In addition, operators have expressed concern regarding the presentation
of warnings that can be detected by passengers. Bus passengers may find
warnings for advance cues of potential threats to be annoying and
potentially alarming. There is a lack of past human factors research in
FCWS within the transit environment. Topics that need further
examination include visual display placement, warning thresholds for
both advanced cues and critical warnings, and the impact of transit
specific driving tasks.

Despite the differences between the collision warning applications, the
FCWS for transit buses requires the same functional elements that are
used by other CWS. A principal functional element of a CWS is sensing
and detection of presence of an hazardous object. This function must be
able to match the environment in which it is intended. A second
functional element is the warning generation function that: (1)
processes the sensory information to "detect" the targets that may
potentially collide with the bus, (2) determines the threat level, and
(3) generates warnings at an appropriate time. The third functional
element is the Driver Vehicle Interface (DVI), which communicates the
warning message to the driver. Fig. 2 depicts the functional description
of the collision warning system.

  -----------------------------------------------------------------------

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Fig. 2 Frontal collision warning system functions

The project team, under the direction of the Federal Transit
Administration (FTA) and with the support of the FCWS Advisory
Committee, conducted research on the requirement specifications for FCWS
for transit buses. The scope of the project includes:

-   Perform literature and national data review

-   Analyze frontal collision accidents

-   Develop a definition of FCWS functions and preliminary functional
    requirements

-   Develop a data acquisition system for data collection

-   Collect data

-   Study approaches for the FCWS

-   Design collision warning scheme and algorithm

-   Build and test the FCWS

-   Perform field verification and validation tests

-   Develop requirement specifications

In addition, following the requirement analysis process defined under
the System Engineering Process (SEP), the team emphasized the following
aspects of the analysis:

\(1\) Data collection and analysis: In order to define the operational
environment and the bus operation scenarios, a thorough data collection
and analysis effort was conducted, which established a foundation for
the determination of sensor performance and system specifications and
for the definition of the performance requirements.

\(2\) Study of driver needs: As bus drivers are the intended users of
the transit FCWS, it is important to form the requirements and to
develop the FCWS to meet the driver's needs. To do so, the FCWS team has
closely interacted with SamTrans drivers to understand their needs,
expectations, operational environment and to define system boundaries.

\(3\) Verification of requirements through field testing: In order to
verify that the performance requirements developed under this project
are indeed within a reasonable and reachable range, a prototype FCWS was
developed and instrumented on three SamTrans buses. Field testing of the
system under regular service provides valuable inputs to the development
of the requirements.

This report summarizes the development efforts conducted in conjunction
with the development of performance specifications for FCWS for transit
buses.

Background

In order to understand the goal of the IVI program and the status of the
development of a Frontal Collision Warning System (FCWS), the project
team has been conducting a continuous literature review.

Transit IVI

The Transit IVI Committee, composed of the FTA, representative transit
agencies, manufacturers, and academia, have identified four user
services as high priority transit IVI services, using systems that
enable drivers to process information, make better decisions, and
operate vehicles more safely:

\(1\) Lane Change and Merge Collision Avoidance

\(2\) Forward Collision Avoidance

\(2\) Rear Impact Collision Mitigation

\(2\) Tight Maneuvering/Precision Docking

These services focus particularly on the safety of the driver (and
indirectly both passengers and pedestrians) and the vehicle in
preventing accidents.

Following a recommendation by the Transit IVI Steering Committee, a
study was conducted by Volpe Center to identify and prioritize transit
industry requirements and problems involving IVI technologies \[1\].
This study concluded that although the total number of accidents
involving transit buses is relatively small within the national accident
data statistics, accidents involving transit buses do result in
significant social and economic consequences. The study further
indicated that the largest single cost component among the economic cost
of motor vehicle accidents of all vehicles, is property damage, which
accounted for over one third of total costs. Of equal or greater
importance is the safety of the bus passenger and pedestrian public.
Among the transit-related IVI applications that have potential to boost
safety and efficiency, in-vehicle collision avoidance/warning systems,
and in-vehicle obstacle and pedestrian warning systems are listed as
highest priority.

The Volpe study further pointed out that the transit industry, with
increasingly restricted funding, finds itself bearing the cost of
expensive technologies and infrastructure necessary to support their
systems. Transit managers cannot afford to be adventurous. There tends
to be a reluctance to "be the first" or to be the testing ground in
public arenas. There is also a perception in the transit industry that
the deployment of new technologies is high-risk. Additionally, there is
the need to obtain acceptance from unions where implementing technology
changes will affect individuals' jobs. The importance and uniqueness of
the existing transit infrastructure must be recognized. Any deployment
of new technologies should be synergistic with existing infrastructure,
thus eliminating the need to create new infrastructure accoutrements.
Recognizing these unique transit characteristics, it is important for
the IVI program to develop collision warning technologies that meet
specific transit needs and to conduct field testing to demonstrate
system feasibility and cost effectiveness.

Status of Development of FCWS

From recent literature, it was found that significant studies have been
conducted in various aspects of CWS designs for transportation
applications. Research and development efforts were evenly distributed
in industrial, academic, and governmental sectors. In the last five
years, the publications have been quite intensive, indicating that
research and development results have gradually materialized and that
systems have been commercially deployed. Among the topics of research
and developments within this review, there are studies across a diverse
range of subject areas. Research and development are documented in the
following areas:

Accident Statistics in Publications

Wilson \[2\] stated that data from the General Estimate System (GES) and
the National Highway Traffic Safety Administration (NHTSA) Fatal
Accident Reporting Systems (FARS) showed that rear collisions are 23% of
all police reported crashes per year. Among them, 77%-84% are caused by
driver inattention, and 7%-18% are caused by following too closely.

In another publication \[3\], statistics showed that 85% of rear-end
collisions involved two vehicles; equal occurrence at intersection and
non-intersection; 91% on straight road, 60% on dry roads; 75% in
well-lit conditions; 67% without injuries. GES from 1992 data showed
that 59% are caused by the leading vehicle having stopped; 37% by the
leading vehicle decelerating; 80% in clear weather and 70% under
well-lit conditions; 73% on dry roads; 95% on straight roads.

Asher \[4\] reiterated that about 20-25% of accidents are rear-end
collisions and reported that about 60% rear-end collisions could be
avoided if the driver had an additional 0.5 sec of warning before the
incident.

It was estimated in another publication \[5\] that rear-end crashes
accounted for 24% of all crashes from NHTSA research. These crashes
occurred mostly during the daytime (77%), on straight roads (90%), and
under dry weather conditions (79%).

The National Automotive Sampling System (NASS) GES provided the most
usable data about all types of crashes and related vehicle types. By
restricting attention to police-reported crashes, the GES concentrates
on those crashes of greatest concern to the safety community and the
general public. The GES data was supplemented by direct transit industry
input. The five most frequent crash types involving motor coaches are:
lane change, rear end, intersection, with a parked vehicle, and backing
up scenarios. The total for the top five crash categories comprises
approximately 87% of crashes involving motor coaches within the United
States.

The study by Volpe that focuses on nationwide collision statistics has
concluded that the highest-accident-rate-and-severity-rating accident is
intersection type of crashes where a bus is struck by another vehicle.
The second major scenario is rear-end type of collisions where a bus is
struck by another vehicle. These two types of crashes account for almost
one third of the top five scenarios. The mid-level types of accidents,
which carry a medium range of risk and severity, include the other half
of the intersection type of accidents where the bus strikes another
vehicle; rear-end type where the bus does the striking, and both backing
up type of crashes. There remains a critical need for gathering real
life data that is transit specific. In order to specifically evaluate
the effectiveness of IVI technologies, the accident data needs to be
more specific with respect to the accident characteristics, including
causal factors. All transit IVI projects should require a detailed
accident analysis phase.

Benefits Evaluation from Selected Applications

Farber \[6\] compared two collision-warning algorithms: Closing Rate
Algorithm (CRA) and Stopping Distance Algorithms (SDA). It was estimated
that SDA provides advanced warning and eliminates 95-100% crashes, but
it also produces a substantial volume of incorrect warnings. CRA
provides last moment warnings and only eliminates 65-70% of crashes, but
it produces fewer incorrect warnings. This illustrates that a compromise
may be necessary between frequent warnings and false alarms.

In a study \[7\] of CWS for commercial trucks, it was found that a 37%
reduction of hard braking of 0.25g (1g = 9.8m/s^2^) or greater could be
achieved. This led to a 2-10% reduction in fuel consumption. In one
test, fuel savings as high as 20% was obtained. In a separate field
review \[8\] of CWS for heavy-duty trucks, it was revealed from a survey
of 171 drivers that 80% changed their way of driving, which had a
positive effect.

An evaluation of Adaptive Cruise Control (ACC) \[9\] showed that if the
automated braking function was incorporated into ACC, the total number
of accidents and fatalities can be reduced by up to 85-90% and 30-80%
respectively.

Even though these evaluation studies have been conducted for different
settings and applications, they show that the deployment of CWS
potentially can reduce accident numbers and fatalities. It is also
significant that by alerting the driver to obstacles ahead there might
be a reduction in hard braking which will result in smooth maneuvers,
thus leading to fewer passenger falls in the case of transit bus
operations.

Sensors

Most collision warning systems demand the use of radar or optical
sensing devices. The descriptions of the sensor performances or their
design issues have been examined in numerous reports, such as those in
\[8,10,11,12,13,14\]. Wilson \[2\] gave a comprehensive review of
performance guidelines for radar or other forward-looking sensors in the
requirements for range, and lateral and vertical field of view. However,
those guidelines are given for passenger cars for use in mainly highway
applications.

Human Factors Research

Past human factors explorations of forward collision warnings have
emphasized scaled time-based headway \[15 & 16\] and binary warnings
\[17 & 18\]. Time-based warnings, often formulated using
Time-To-Collision (TTC), have been championed as they are less affected
by speed when compared to distance-based warnings. Furthermore, they
relate well to models of how drivers maintain longitudinal separation
\[19\].

Binary warnings are more often used for critical scenarios where early
warnings would not be possible. For example, a simulator study on how
people responded to vehicles cutting in from parked positions compared
icons, text commands (\"Swerve Left\"), and the baseline case of no
warning \[18\]. In some scenarios it will be impossible for sensors to
provide advanced cues to alert the driver to potential threats. In these
events, the system will need to proceed directly into a full warning
state, thus emulating a binary warning interface. The aforementioned
study did find that drivers were able to gain some benefit from the
binary warning.

Recent work on snowplows has used distance-based displays \[20\] as they
were deemed easier to transition to should a sudden period of low
visibility (e.g., a white-out) obscure an actively watched forward
obstacle. As low visibility is a rare event for a bus, a time-based
approach is probably more suitable. The research on snowplows also
deemed binary warnings unsafe given the likelihood of low traction, a
scenario that is also conceivable for transit during adverse weather.
Furthermore, sharp braking or swerving actions are not desirable within
the transit community due to passenger falls. This suggests that binary
warnings requiring fast intervention are not preferable for transit
applications.

In fact, most literature on visual warnings for CWS applications
suggests a graded approach to warnings \[16,21,22,23,20\]. This commonly
involves a scale of some sort implying increased danger. Also commonly
suggested is the use of auditory warnings when TTC has reached a
critical point and braking action is sorely needed. In fact, auditory
tones are incorporated into the Eaton-Vorad CWS, which is offered by
several truck Original Equipment Manufacturers (OEM) as an option.
Research on strictly auditory warnings has also shown beneficial results
\[17\]. Extending this notion was a government-funded study on the value
of localized auditory warnings to assist drivers in identifying the
location of hazards \[24\]. While the results suggested that such a
feature is promising, the authors also found that such a system requires
special care with respect to speaker location and sound choice.

## References {#references .Style-Heading-2-+-Justified-Left:--0\"-First-line:--0\"-Before:--1...}

1.  Intelligent Vehicle Initiative Needs Assessment, FTA-TRI-11-99-33,
    DOT-VNTSC-FTA, November 1999.

2.  T. Wilson, et al., "Forward-Looking Collision Warning System
    Performance Guidelines," SAE No. 970456, 1997.

3.  T. Wilson et al., IVHS Countermeasures for Rear-End Collisions,
    Task1, Volume II: Statistical Analysis, DOT HS 808 502, 1994.

4.  H. Asher, B.A. Galler, "Collision Warning Using Neighborhood Vehicle
    Information," Proceedings of ITS America, 1996.

5.  S. K. Kenue, "Selection of Range and Azimuth Angle Parameters for a
    Forward Looking Collision Warning Radar Sensor," Proceedings of
    Intelligent Vehicles, 1995.

6.  E. Farber, "Using the REAMACS Model to Compare the Effectiveness of
    Alternative Rear End Collision Warning Algorithms," Proceedings of
    IVHS America, 1994.

7.  J. Woll, editor, "Radar-based Adaptive Cruise Control for Trucks,"
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8.  H. Fukuhara, K. Kunihiko, "Essential Issues involved in Radar-Based
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    1994.

9.  N. Takubo, "Influence of Adaptive Cruise Control on Rear-end
    Collisions," Proceedings of ITS America, 1995.

10. R. Tribe, et al., "Collision Warning," Prometheus -- Future Systems,
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11. W. Ulke et al., "Radar Based Automotive Obstacle Detection System,"
    SAE 940904, 1994.

12. M. Hischke, "Collision Warning Radar Interference," Proceedings of
    Intelligent Vehicles, 1995.

13. M. Hischke, "Interference Resistance Signals for Collision Avoidance
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14. C. Eckersten, et al., "A High Performance Automotive Radar for
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15. A.D. Horowitz, "Warning Signal Design: A Key Human Factors Issue in
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16. T. Dingus, et al., "Human Factors Field Evaluation of Automotive
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17. M. Vercruyssen, et al., "Automobile Braking Response Speed: Age
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    1996 Annual Meeting of ITSA (pp. 958-965), 1996.

18. H. Yoo, et al., Automotive Collision Warning Effectiveness: A
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    UMTRI-96-29), Ann Arbor, MI: The University of Michigan
    Transportation Research Institute, 1996.

19. J.A. Misener, et al., "A Focused Examination of Critical Factors and
    the Emergence of a Cognitive Car Following Driver Model for Rear-End
    Crashes with a Stopped Lead Vehicle," Transportation Research Board
    79th Annual Meeting, 2000, Accepted for Transportation Research
    Record.

20. Steinfeld, A. H-S. Tan, "Development of a Driver Assist Interface
    for Snowplows Using Iterative Design," accepted for Transportation
    Human Factors. Intelligent Vehicle Initiative Needs Assessment,
    FTA-TRI-11-99-33, DOT-VNTSC-FTA, November 1999.

21. R. Graham, S. Hirst, "The Effect of a Collision Avoidance System on
    Drivers\' Braking Responses," Proceedings of the 4^th^ Annual
    Meeting of IVHS America (pp. 743-749), 1994.

22. T. Wilson, et al., "IVHS countermeasures for rear-end collisions,
    driver warning system performance guidelines, "Proceedings of the
    1996 Annual Meeting of ITSA (pp. 949-957), 1996.

23. T. Dingus, et al., "Human Factors Design Issues for Crash Avoidance
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    Erlbaum Associates, 1998

24. A.K. Tan, N. Lerner, Acoustic Localization of In-Vehicle Crash
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    1996.

[^1]: Formally Assistant Research Engineer, PATH