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Visualization of Traffic Accidents

Jie Wang; Yuzhong Shen; Asad KhattakVirginia Modeling, Analysis, and Simulation Center, Old Dominion University

{jwang016, yshen, akhattak}@odu.edu

Abstract: Traffic accidents have tremendous impact on society. Annually approximately 6.4 million vehicleaccidents are reported by police in the US and nearly half of them result in catastrophic injuries.Visualizations of traffic accidents using geographic information systems (GIS) greatly facilitate handling andanalysis of traffic accidents in many aspects. Environmental Systems Research Institute (ESRI), Inc. is theworld leader in GIS research and development. ArcGIS, a software package developed by ESRI, has thecapabilities to display events associated with a road network, such as accident locations, and pavementquality. But when event locations related to a road network are processed, the existing algorithm used byArcGIS does not utilize all the information related to the routes of the road network and produces erroneousvisualization results of event locations. This software bug causes serious problems for applications in whichaccurate location information is critical for emergency responses, such as traffic accidents. This paper aimsto address this problem and proposes an improved method that utilizes all relevant information of trafficaccidents, namely, route number, direction, and mile post, and extracts correct event locations for accuratetraffic accident visualization and analysis. The proposed method generates a new shape file for trafficaccidents and displays them on top of the existing road network in ArcGIS. Visualization of traffic accidentsalong Hampton Roads Bridge Tunnel is included to demonstrate the effectiveness of the proposed method.

1. Introduction

Driving is an essential part of day-to-day life formost people. However, with so many people onthe road with varied physical and psychologicalconditions, driving an automobile is usually a riskyand dangerous activity. According to the reportreleased by police, annually there areapproximately 6.4 million vehicle accidents in theUS and nearly half of them result in catastrophicinjuries [1 J. Besides various precautions againsttraffic accidents, prompt and efficient trafficaccident handling is very important for saving livesand reducing the adverse impact caused by trafficaccidents.

Geographic information systems (GIS) arecomputer-based systems used to store,manipulate, display, and analyze geographicinformation. Various GIS software tools havebeen widely used in transportation research andmanagements for many years due to theirpowerful geo-visualization capability, analyticalcapability and database management features [2J.Visualization of traffic information greatly improvedthe performance and efficiency of many trafficrelated applications such as traffic supervision,traffic scheduling, and so on. Among theseapplications, transportation safety can significantlybenefit from the use of GIS [3J. Visualization oftraffic accidents using GIS can greatly facilitatehandling and analysis of traffic accidents in many

aspects. The locations of traffic accidents areespecially critical for rapid response of trafficaccidents. Visualizations of traffic accidents overa large area can provide useful statistics andinsight into the condition and state of thetransportation network.

Environmental Systems Research Institute (ESRI),Inc. is the world leader in GIS software [4J. ArcGIS,a software package developed by ESRI, has thecapabilities to display events associated with roadnetworks. But during processing of the eventlocations related to the road network, the existingalgorithm used in ArcGIS ignores the routedirection information of the location and results inerroneous visualizations of the event locations.For example, the algorithm used in ArcGISconsiders the route 1-64 E and route 1-64 W as thesame route although in fact they are two separateroutes. This software bug causes seriousproblems for applications in which accuratelocation information is critical for emergencyresponses, such as traffic accidents. In this paper,we describe a method that can extract correctevent locations and create accurate visualizationsof traffic accidents. The proposed methodgenerates a new shape file for traffic accidentsand displays them on top of the existing roadnetwork in ArcGIS.

The remainder of this paper is organized asfollows. Section 2 introduces the method used by

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ArcGIS that produces erroneous results. Section3 discusses the proposed method and its resultsand compares them with those produced byArcGIS. Finally conclusions are drawn in Section4.

2. ArcGIS Algorithm

Route events can be added to ArcGIS in two ways:1) using the Make Route Event Layer geo­processing tool; or 2) accessing the Add RouteEvents wizard from the ArcMap tool menu [3]. InArcGIS, information about route events is storedin an associated table. Route is a link featureclass with an identifier field for every record, whichcan be used as a reference in the event table.The route information is stored in a shape file thathas associated attributes. To display route eventson a road network, parameters of the relationshipbetween the table storing events and the shapefile that stores the routes should be defined first.The event table should also contain a field thatindicates the measure or the precise location ofthe event. Figure 1 shows the graphical userinterface in ArcGIS that is used to select the routefile, route identifier, event table and measure field.In this paper traffic accident data provided by theVirginia Department of Transportation is utilized toillustrate and compare the results produced byArcGIS and the proposed method.

In Figure 1, the drop-down box Route Referenceis used to select the shape file that contains theroad network, including all routes. The drop-downbox Route Identifier is used to specify the attributeof the road network shape file that identifies theroute, which happens to be ROUTENUMBER inthe example shown in Figure 1. The filecontaining the route events is then selected viathe drop-down box Event Table. The same fileshould also contain a field for identifying the route.As shown in Fig. 1, route events can be eitherpoint type or line type. For traffic accidents, theevent type is point type representing the trafficaccident locations. A Measure is needed tospecify the locations of point events and in thiscase RouteMilePost is used to specify the trafficaccident locations, which is the distance from thestarting point of the route. ArcGIS only makes useof the attributes specified in Table 1 and Table 2for visualization of route accidents. It can be seenthat the directions of the routes are ignored byArcGIS, e.g., routes 1-64 East and 1-64 West aretreated as the same route. Thus accidents areplaced randomly along either direction of a routedepending on the record location in the binaryshape file. In the example shown in Figure 3, alltraffic accidents are erroneously placed on 1-64East.

Table 1: Event table utilized by ArcGIS

Table 2: Route Table Utilized By ArcGIS

144

259

264

294

264

249

0064

00640095

006400664

00265

00264

0095

0064

0064

0064

00264

00265

00664

Polyline M

Polyline MPolyline M

Polyline M

Polyline M

Polyline M

Polyline M

I~

r W., ... f ... .....e.o....Mvt:teaCStld~.......,..j~ I ~~

Figure 1: Interface for adding route events inArcGIS

Sc>ecfy"""'"-- ......0-.,............_ .._"" ,.....e-tr.... !C\IJoon\Somee'-\OeoIdq>v3~

-- IRJUTENUNBE 3O'OOM" fWM; d lMriI..tMe CIOfbhI

r. Pen EYwiI: Occu It • poecilre IocIticn aIang a LO..te

,. lne&ertt OlII'he.~pcltiand.ftllJe

Ro&u..,.-u ..oI:tedt ....~--.nd~~.. AuIlIeCO"'Ui*lg JO.ia..,.... e-t be added _ hi~_~•.

Sc>ecfy __... Ihe ................

-""' , I--~ :::J~fbi. _ Ir=RJ-UTEH=""u"...MB-E----3~.

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3. Proposed Method

To address the problems in ArcGIS for trafficaccident visualization, we developed a programthat utilizes all the relevant information in the routetable and event table for identifying accidentlocations. Specifically, the attribute Route Suffixin both tables are utilized, which indicates thedirections of the routes. Some attributes of theevent table and route table are shown in Tables 3and 4, respectively. The block diagram of theproposed method is shown in Figure 2.

Read road network shapefile and its attribute table

L-~

Read traffic accidentdatabase

l--~

Identify accident routesusing both route numbers

and directions

+Find the polyline in theroad network file thatcontains the accident

locations

L~

Convert the accidentlocation from mile post to

latitude and longitudeusing linear interpolation

~Write all the accidentlocations into a newshape file with point

features

L~

Visualize the new pointshape file on top of the

road network

Figure 2: Block diagram of the proposed method

The proposed method first read the input files,including the shape file containing the roadnetwork, its associated attribute table, and thetraffic accident database. Then it identifies trafficaccident routes using both route numbers anddirections, Le., the attribute Route Suffix. In ashape file that contains a road network, eachpolyline is a part of roadway that consists of aseries of vertices. The minimum and maximummile posts of a polyline are stored as attributes ofthat polyline. Thus, based on the attributeRouteMilePost of the accident location, thepolyline in the road network file that contains theaccident location can be found by comparingRouteMilePost and the minimum and maximummile posts of the polyline. After the polylinecontaining the accident location is identified, weneed to further to find the two consecutive verticesof that polyline between which the accident islocated. Each vertex of the polyline in a roadnetwork has three attributes: latitude, longitude,and mile post. The latitude and longitude of theaccident location is computed as linearinterpolation of two vertices based on the mileposts. Finally, the accident locations are writteninto a new shape file with point features and it isimported into ArcGIS and visualized on top of theoriginal road network. Figure 4 shows the resultsgenerated by the proposed method. It can beseen that traffic accidents are correctly displayedalong both directions of Interstate 1-64. Figures 5and 6 show enlarged views of Figure 3 and 4. Itcan be clearly seen that the proposed methodcorrected the error in ArcGIS.

The implementation of the proposed methodutilized the Shapefile C Library (5), which providesthe ability to read, write, and update ESRI shapefiles (.shp) and associated attribute files (.dbf).

Table 3: Event table utilized in the proposedapproach

~~I~.~=-_.~

0 0064 - 264 W

1 00264 - 249 E

2 00664 - 259 W3 0064 - 294 E

4 00265 -- 14 W

5 0095 - 4 N

6 0064 - 264 W

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Table 4: Route table utilized in the proposedapproach

- - r--:- ~

II

II

Polyline0 - 0064 W0 M

1Polyline

1 - 00264 EM

Polyline 2-

00664 W2 M

3Polyline

3 -- 0064 EM

Polyline 4 -- 00265 W4M

5 Polyline 5 -- 0095 NM

4. Conclusions

Visualization of traffic accidents can greatlyfacilitate handling and analysis of traffic accidents.ArcGIS is the leading GIS solution provider and itssoftware ArcGIS supports visualization of routeevents, such as traffic accidents. However, thedefault algorithm of ArcGIS does not considerroute directions when displaying route events, andthus producing erroneous visualizations. Thispaper proposed a method that utilizes all relevantinformation of traffic accidents, namely, routenumber, direction, and mile post, and extractscorrect event locations for accurate traffic accidentvisualization and analysis. The proposed methodgenerates a new shape file for traffic accidentsand displays them on top of the existing roadnetwork in ArcGIS. Included visualization of trafficaccidents along Hampton Roads Bridge Tunneldemonstrated the effectiveness of the proposedmethod.

•

Figure 3: Traffic accidents displayed along HRBridge Tunnel (1-64) generated by ArcGIS. All theaccidents are errorneouly placed along 1-64 Eastbecause ArcGIS discards the route directions.

"

"

"

Figure 4: Visualization of traffic accidents by theproposed method. Traffic accidents are placedcorrectly along both directions of 1-64.

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Figure 5: Enlarged view of traffic accidentsdisplayed along HR Bridge Tunnel (1-64 East)generated by ArcGIS. All accidents are placedalong 1-64 East.

REFERENCES1. National Highway Traffic Safety Administration.

Traffic Safety Facts, 2000: Overview. DOT HS809 329. Washington, DC: Department ofTransportation, National Highway Traffic SafetyAdministration.

2. Thill, J.C., (2000) Geographic informationsystems for transportation in perspective.Transportation Research Part C, 8(1-6): p. 3-12.

Figure 6: Enlarged view of traffic accidentsproduced by the proposed method. Accidentsare placed correctly along both 1-64 East and 1­64 West.

3. Kim, K. & N. Levine, (1996) Using GIS toimprove highway safety. Computers,Environment and Urban Systems. 20(4-5): p.289-302.

4. ESRI, (2009) http://www.esri.com/.

5. Shapefile C Library V1.2, (2009)http://shapelib.maptools.org/.