IMPLEMENTING GLOBAL POSITIONING (GPS) COORDINATES
IN SOUTH CAROLINA
TRAFFIC RECORDS SYSTEM
The use of the State’s milepost collision location system was not accurate and consistent enough to provide reliable data to the South Carolina Department of Transportation (SCDOT) and the South Carolina Department of Public Safety (SCDPS). Accurately locating traffic collisions enables high crash collision locations to be identified for law enforcement and engineering countermeasures. State hazard elimination funding is based on the identification of high collision locations that can only be accomplished with reliable and accurate crash location data. If an agency is not providing accurate collision location data, local communities will not have the opportunity to obtain State funding for countermeasures to reduce motor vehicle crashes.
The goal of this program was to provide law enforcement agencies with GPS devices to collect accurate traffic collision location data. The coordinates would be entered in the Latitude and Longitude fields already existing the South Carolina Traffic Collision Report Form (TR-310). The intent was for law enforcement agencies to use the GPS devices to obtain the latitude and longitude coordinates for every collision in South Carolina. It was determined that the format of the coordinate data would be degrees, minutes, seconds or dddºmm’ss.s”. The coordinate data would be entered on the report in the same manner as all other collision data elements gathered at the scene of the crash.
The South Carolina Department of Transportation, with the support of the Federal Highway Administration, purchased 1,900 Garmin eTrex Legend GPS units. In the fall of 2003, these Global Positioning System (GPS) units were transferred to the South Carolina Highway Patrol (SCHP). The South Carolina Highway Patrol then contacted other states to develop a curriculum for training on these devices. They conducted train-the-trainer sessions with state and local law enforcement agencies. These law enforcement agencies were issued an appropriate number of GPS devices after they had successfully completed the training and with instructions that they would be issued to officers that investigate motor vehicle crashes. The newly trained officers then returned to their agencies to train their contemporaries in their law enforcement agencies.
The South Carolina Department of Motor Vehicles began receiving TR-310 crash reports from law enforcement agencies with GPS location data entered in November 2003. In 2004, approximately 85% of all TR-310 reports contained GPS location data. To examine and determine the quality of this data being gathered and submitted by law enforcement, the data was mapped using ESRI ArcMap software. The resulting maps indicated that there were large number of the collision records that had incorrect GPS data points entered on the TR-310. Analysis of the data indicated that the GPS unit is capable of obtaining accurate and reliable latitude and longitude data at a collision site. However, the accuracy of the data could vary by as much as 200 feet based on the collision environment location (topography) and inadequate satellite coverage (the unit was not held at the location long enough for three or more satellites to lock the correct coordinates). The source of other data errors included incorrect formatting of the GPS unit, GPS data incorrectly written on the TR-310 report, and GPS data incorrectly entered into the computer system via the data entry process. The actions necessary to significantly improve the accuracy of the GPS data are manageable and relate to training, proper use of the GPS unit, care when placing the GPS data onto the TR-310, and care when entering the GPS data into the State’s computer system. A refresher in-service training document was created and is being distributed to law enforcement officers in the State to address these problem areas.
The South Carolina Department of Transportation (SCDOT) purchased 1,900 GPS units for approximately $366,400
Tami Upchurch
Statistical Research Manager
South Carolina Department of Public Safety.
P.O. Box 1993
10311 Wilson Blvd.
Blythewood, SC 29016
(803)896-9941
Terecia Wilson
Director
Safety Office
South Carolina Department of Transportation
955 Park Street
Columbia, SC
29201
(803) 737-0403
Jake Brewbaker, PMP, CSPM
SCCATTS Project Manager
SCDPS-South Carolina Department of Public Safety
P.O. Box 1993
10311 Wilson Blvd.
Blythewood, SC 29016
(803) 896-7519
jakebrewbaker@scdps.net