The Good, the Bad and the Ugly of GPS Safety Data: Examples of GPS Located Safety Data

2010 Ohio GIS Conference

September 15-17, 2010

Crowne Plaza North Hotel

Columbus, Ohio

2010 Ohio GIS Conference

September 15-17, 2010

Crowne Plaza North Hotel

Columbus, Ohio

Jeremiah Glascock

Safety Systems Manager

Traffic Safety Analysis, Systems & Services, Inc.

Scrubbing and Locating Crashes StatewideTSASS has worked or working with 20 counties and three MPO’s statewide representing almost 50% of all crashes.

Safety funding programs are data driven and require three full years of scrubbed and located crash data.

TSASS has a statewide crash data and crash report image repository going back to 1995.

Our goal is to promote and help local governments to apply for safety funds that they otherwise would not have the resources to do so.

LBRS allows TSASS and in turn the locals, to successfully , efficiently and accurately improve hazardous intersections.

For ore information on LBRS and safety data, see the DDTI and TSASS joint presentation today at 3:30pm.

Location Error Statistics 83,867 crashes were scrubbed in 2009 under contracts with

MPO’s, County Engineers and Engineering Firms. Of those under contract there were 29,784 crashes identified

as problems affecting the location of the crash and corrected. 17,556 crashes not under contract to be scrubbed but were

identified as problems affecting the location of the crash. 1 out of every 10 crashes have some problem associated

with the location of the crash.

Locating Safety Data•Methods

•Using the Officer’s description of the crash.•Taking the information from the OH-1 Crash report including the narrative and diagram to locate the crash to the best available base files.•Once the NLFID (unique route identifier) and log point mileage is found for the referenced location, the coordinate data is then geocoded.•LBRS datasets are key to the successful and accurate location.•If roads are realigned or a bypass put in, for example, the crashes do not move with the roadway.

•Using the Officer’s GPS coordinates.•Identify the coordinates’ validity.•Determine if the coordinates correspond to the description.•Using rules, choose the “best” location (ether the GPS or description).

Safety Data and GPS Beginning with the Ohio Crash Report revised in 2000,

crashes have been reported with coordinate data. Officers and the Engineering community still completed and

depended on the tradition location information as the primary identifiers.

Up until recent, GPS coordinates were not trusted for many reasons: Data was being keyed into the ODPS database from report. Most law enforcement agencies did not have GPS devices.

GPS Data Reporting Trends• With the rapid

technological advances in GPS handheld devices, crashes are being located with coordinate data more frequently.

• Less than 1% of all crashes statewide had coordinate data in 2002 compared to better than 26% in 2009.

Ugly GPS Data Collection Crashes with coordinates:

Not in the Country! Not in Ohio! Not in the reported county! Invalid Coordinates!

This one could be a keyed error. Perhaps it should have been 40° 3' 20.87” , -82° 43' 43.54“…. We hope?

Still no luck… but where is the REAL location… we must resort to the traditional locating methods.

Not in the Country!…

The correct coordinates for this intersection are not 40° 3' 20.87” , -22° 43' 43.55“ or 40° 3' 20.87” , -82° 43' 43.54“ but 40° 3' 20.2752“ , -82° 24' 42.8646"

In Lake Erie… more than 30 miles from I-90

We have GPS and no location information. So where will these coordinates put the crash?

Not in the State!…

Not in the State…

We have both GPS and location information… now which is correct?

The coordinates based on the location description are 82°37'20.135"W 38°29'55.662"N; 130 miles from the GPS. We can not trust the GPS coordinates and must rely on the officer’s location description.

Not in the State…It couldn’t really be in Missouri could it? Maybe he meant to put 40° 14' 7.15", -83° 49' 17.15“ instead of40° 14' 7.15", -93° 49' 17.15“, but will that put it near the correct location?

If it was assumed that the officer meant to put 83 degrees instead of 93 degrees, that still puts us more than 33 miles from the location information described at the top of the report.

Not in the County!…

This is Wayne County

These coordinates indicate the crash is in Mahoning County…. Wrong County!

Invalid Coordinate Data…

Bad GPS Data Collection Clustered at gas stations or waypoints. In farm fields or lakes. Far removed from any roadway. Not near the reported location as witnessed by the officer.

What do these three crashes have in common?It’s not location…It’s the coordinates!!! Where are these coordinates?

They are still in Greenfield, Ohio but definitely not at the correct locations…

In Dow Lake! Really? This information looks pretty good!

Now that’s bad…

Invalid GPS (not near Roadway)…

These GPS Coordinates put the crash in the correct county… but are they correct?

4620 Feet

That’s bad too…

Good GPS Data Collection GPS has been taken at the point of impact (or close to it). Coordinates match the reported location information.

Coordinates collected at Point of Impact…

Coordinates match the officer’s diagram!

2009 GPS Error Statistics In 2009 there were 80,772 crashes that had Latitude and

Longitude values. 60,750 had valid Latitude and Longitude within the State of

Ohio. 17,739 had invalid Latitude and Longitude. 2,283 either had a Latitude and no Longitude or vise versus. Of the 80,772 with GPS 1 out of 3 had issues with GPS.

Either too far from nearest road centerline or invalid.

Where are these erroneous coordinates coming from? Rounding or transposing numbers. Not reporting enough decimal places. Clearing the scene and collecting GPS at other locations. Electronic safety data is still being printed out at the

enforcement post and sent to ODPS, where it is then keyed in to the database.

Why is this important? A degree of latitude is approximately 69 miles, and a minute of

latitude is approximately 1.15 miles. A second of latitude is approximately 0.02 miles, or just over 100 feet. If the reported coordinates are rounded to the nearest second, the location

could be off by 100 feet. Transposing the minutes has the potential of throwing off the location by

several miles or more.

For safety improvements, crashes are summarized to intersections if they are within 250 feet of the intersection.

How Quality of GPS Collection Affects the Public Safety and Safety Improvement Projects

Good GPS collection allows the engineering community to accurately and efficiently analyze safety data.

Proper collection means less crashes in lakes or in high school parking lots.

Questions, Comments?Jeremiah Glascock

Traffic Safety Analysis Systems & Services http://osisportal.tsass.com(614) 539-4100 (614) 302-8183jglascock@tsass.com