Evaluation Of The Locations Of Kentucky’s Traffic Crash DataEric Green, GISP, MSCE, PE

Background

• Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU)

• Traffic Safety Information System Improvement Grants available to states under section 408 of the bill

• Follow-up to 2004 study:• "Evaluation of the Accuracy of GPS as a Method of Locating Traffic Collisions"

• Accurate crash locations:• Crash rates, highway improvement, education and enforcement efforts

Outline

•Methods for locating a crash for a Kentucky police officer•Review of a random sample of crash data•Analysis of current location data•Where should a crash be located?•Conclusions / Recommendations

Paper Reports

• Submitted manually

• GPS from Magellan, Google® Maps, 911 system

• County, Route and Milepoint (CRMP) using reference system

eCrash KYOPS

• MapIt• Added October 1st

2007• CRMP data linked to

GPS• Between/Intersect

streets• Searchable• RT Unique:“034-US-0068 -000”

Previous Report

• Crash data from January to June of 2003• Lat/Long added in 2000, required June 1st,

2002• Accuracy by County, Route and Milepoint

(CRMP)• Linear reference system• 55% correct

• Accuracy by GPS• Using Magellan SporTrak handheld unit• 58% correct

Random Sample• 222 random crashes from 2009 were reviewed• All had Lat/Long generated by the MapIt system• This was considered the reported location

• The actual location was derived from:• Report narratives• Addresses• Intersecting or between roads

• The accuracy of each location was classified:• YES – within 500 feet of actual location• NO – outside of 500 feet from actual location• UNKNOWN – unable to determine actual location

Random Sample• Each report was classified as:• Intersection• Between Streets• None

• 500 feet is useful for network screening but more accurate locations are preferred for individual crash analysis

• A range was given for each crash indicating accuracy of each presumed locations• Definitive locations such as addresses had small or ranges

of zero• Larger ranges were used when the location was

determined to be between two reference points

Random Sample ResultsWas location Accurate? Type of Location

Between streets

Intersection None

Grand Total

Yes 100.0% 100.0% 54.6% 71.2%

No 0.0% 0.0% 9.2% 5.9%

Unknown 0.0% 0.0% 36.2% 23.0%

Grand Total 100.0% 100.0%100.0

% 100.0%

Random Sample Results

• If the unknown locations were removed•152 of the 167 or 92% were accurate

• 92% can be compared to a similar study conducted 6 years ago which yielded:•58% were correct by Lat/Long•55% were correct by CRMP

Crashes Coded as Inaccurate

• Lat/Long is not consistent with address/reference (12 crashes)• No reference point (1 crash)• These could be a result of the officer needing to "guess" where to click on the mapping system• Additional reference systems could help minimize this error

Crash Database Analysis

• Latest data containing the MapIt-based location• October 1st, 2007 to December 31st, 2009• 334,354 crashes• Data were plotted using CRMP data• Lat/Long data was assigned to all plotted

CRMP crashes• The distance between the Lat/Long location

and the CRMP location was calculated

Crash Data Potted by Lat/Long

Crash Data plotted by Lat/Long Showing County Check

Crash Data by Year and County Check

Plotted In Reported County?

Year No Yes

2007* 2.7% 97.3%

2008 1.1% 98.9%

2009 0.3% 99.7%Grand Total 0.9% 99.1%*2007 only represents 3 months of the year

Average Distance by Year (Usable)

Row Labels

Average Distance

(Feet)

Average Distance (Miles)

Crash Count

2007* 16,185 3.1 24,874

2008 40,713 7.7 112,434

2009 1,793 0.3 121,066Grand Total 20,115 3.8 258,374

*2007 only represents 3 months of the year

Most Egregious Errors

• The crash database was sorted by distance and several of the most egregious errors were examined• There were two types of electronic

reporting errors that yielded large distance between the CRMP and Lat/Long locations•Lat/Long Glitch• ‘Distance From’ Glitch

Lat/Long Glitch• For several crashes one of the Lat/Long coordinates

was off by -96 degrees• Adding this value to these crashes plotted the crash

very close to the CRMP location• MFN of 70651040

• reported longitude of 7.759983063• longitude based on the CRMP of -88.2399139• 7.76 - 96 = -88.24• The data base actually showed “07.759983-01”

• This was only observed in 252 crashes, most of which were in 2008

• The error was not observed since January of 2009. It is assumed to have been fixed.

‘Distance From’ Glitch• This error was harder to quantify its frequency as

the distance was not nearly as egregious• It was noticed in about 700 crashes (presumed to

be many more)• The GPS coordinates were modified by the ‘distance

from’ field• The office should not need to use the ‘distance

from’ field when using the MapIt system (it is used for CRMP)

• This error is currently repeatable• Perhaps by design, but it was never noticed to be

deliberate

Paper Report Errors• Several of these errors were related to the officer

entering the data wrong or the data being keyed into the system incorrectly

• There were 731 crashes with a Lat/Long minute value 60 or greater

• Over 400 crashes with noticeably bad Lat/Long• Several crashes that had no minutes or seconds

or suspicious values such as 30 minutes• Although these represent a small number of

crashes, they are a much higher proportion when only paper reports (about 27,000) are considered

Adding A County Check• If all crashes that were plotted outside of their

reported county are removed, this distance reduces from 3.8 to 0.2 miles

• This implies that if a county check was performed before accepting a crash that the most egregious errors could be eliminated

• Most of the worst errors occurred prior to 2009• The average distance in 2009 would reduce from

0.3 miles to 0.1 miles by requiring this check• There is a county bounding box check although it

must not be required

Unexpected Error - Unmodified MapIt• Crashes indicating that the officer used the MapIt

system and did not edit its location• It would be expected that the distance between

the CRMP and the Lat/Long locations would be ostensibly zero

• It would be expected to observe rounding and map projection errors that would yield some distance between the two locations

• Unexpectedly, however, there were 5,267 (4.4%) usable crashes in 2009 that used an unedited MapIt location, yet had a distance of 500 feet or more

Unmodified MapIt Error• 6 crashes with a distance over 4,000 miles

(explained by the Lat/Long Glitch discussed earlier)

• There were 12 crashes with a distance of over 20 miles

• The average distance of this dataset was 6.6 miles (1.3 miles excluding the 6 with latitude/longitude errors)

• Several of these crashes were reviewed to determine the reason for these errors

• For 127of the crashes the error seemed to be related to ‘distance from’ error discussed above.

Crash report# 70766928 – Covington Police Department, 10/22/2009

Crash report# 70766928 - Covington Police Department, 10/22/2009

Crash report# 70766928 - Covington Police Department, 10/22/2009

Unmodified MapIt Error Summary• A summary was performed by county-route

combinations• A count of each county-route was compared to the

count of that county-route’s occurrence in all 2009 crashes

• A percentage was calculated based on these two counts• The unmodified MapIt location database represents

4.4% of all 2009 crashes• A percentage higher than 4.4% is overrepresented• Several county-routes had very high percentages

implying that there may be something wrong with these routes in the MapIt database

Unmodified MapIt Error by County-Route

Appendix D-2. The County-Routes with 20 or More Crashes and an Unmodified MapIt Location in 2009 Ordered by Descending Percentage of All 2009 Crashes

County-Route

Number of Crashes in 2009 with Unmodified

MapIt LocationNumber of Crashes in

2009 Percent

Bath @ KY-36 23 25 92.0

Kenton @ KY-1072 139 152 91.4

Hardin @ KY-3005 107 119 89.9

Lewis @ KY-8 39 47 83.0

Pulaski @ KY-914 24 29 82.8

Warren @ KY-185 44 59 74.6

Analysis by Distance Between CRMP and GPS

• Most of the location errors have been addressed and mitigated in KYOPS• Analyze paper reports or electronic

reports with modified MapIt locations•The distance between the Lat/Long and CRMP should be zero for all unmodified MapIt•The averages were not driven down by the frequency of such crashes

Properly Locating a Crash

• Location of the first harmful event• Priority of roadways:• 1. Interstates*• 2. Parkways*• 3. US routes*• 4. KY routes*• 5. All other roads

• Intersection and between used when available

*The lower number should be used if both roads are the same priority

Conclusions/Recommendations• 92% of all crashes were accurate compared to

around 50% in the previous study• Most of this improvement can be attributed to the

implementation of the MapIt system in eCrash• A large majority of incorrectly located were largely

due to a lack of reference points• The MapIt system currently requires user to know

where they are on a map• Identified errors should be investigated by KYOPS

Potential Improvements• Aerial photos• Integrated GPS receivers• Reference log data• Mileposts, bridges, culverts, etc.

• Training• QC of location data, state road preference (the

importance)

• Contact specific agencies or evaluate county data• ‘Distance From’ glitch• Edits to check for county and distance between

CRMP and GPS

Contact Information• Eric Green, M.S.C.E, P.E.

Kentucky Transportation CenterResearch Engineer140C Raymond BuildingUniversity of KentuckyLexington, KY 40506-0281  egreen@engr.uky.eduPhone: (859) 257-2680 Toll Free: (800) 432-0719Fax: (859) 257-1815

www.ktc.uky.edu

http://www.ktc.uky.edu/Reports/KTC_10_16_KSP3_10_1F.pdf

Questions?