Improving Road Safety with Mobile GIS

July 1, 2006 By: Kevin P. Corbley

Across the country, departments of transportation (DOTs) are loading up their geospatial data layers and taking them on the road to map the locations of every pavement segment, traffic sign, and guardrail for which they are responsible. Mobile GIS technology is enabling government officials to take their geospatial information out of the office to the places where it can best be applied — state highways and city streets.

Improved safety is the ultimate goal of DOT activities at all levels of government, and these objectives are cited as primary reasons for deploying mobile GIS. The state of Washington, for example, has initiated a new program that involves mapping every roadside feature, natural or manmade, that a vehicle could strike in its 7,000-mile-long state highway corridor network. Once this immense database is completed, Washington DOT will use it to devise strategies for reducing these types of collisions.

Many DOTs are also taking GIS data into the field to update old data or collect new information and build more accurate inventories of transportation assets, conditions, and locations. In McAllen, Texas, and Chesterfield, Missouri, these mapping projects support maintenance and installation operations, but they're also driven by GASB34, a federal directive requiring state and local governments to maintain accurate asset inventories for depreciation and accounting purposes.

Two GIS interns from the city of Chesterfield, Missouri's Engineering Department use handheld GPS receivers to map pavement sections on a residential street.

"We create inventory management maps that are used for a variety of purposes," said Jason Ridgway, senior engineering technician in the Mapping Section of Chesterfield Public Works Department. "Mobile GIS is the most efficient method we've found to determine what we have and where it's located."

Rating Pavement in Missouri

The Chesterfield Public Works Department began rating the condition of its streets in 1991 in an effort to better schedule their replacement and repair. Each of the approximately 13- × 15-foot concrete slabs that compose a street was ranked on a scale of one to 10, with one being the worst. Crews inspected the slabs, made the rankings, and noted them on paper sketches of the street, which were maintained in CAD (computer-aided design) files. The system was eventually upgraded to include an Access database containing code numbers for street segments.

"The city decided which streets should be repaved by adding up the ratings of all the slabs in a segment and then calculating an average ranking," said Ridgway. "But the [CAD-based] system did not allow spatial analysis of isolated slabs that may be in poor condition, so it was difficult to manage individual slabs."

After the federal government introduced GASB34 in 1999, the Engineering Department of Chesterfield Public Works significantly expanded its use of geospatial technology. It enhanced citywide GIS data and deployed GPS receivers to record the locations of all of its street signs and trees. The department created GIS-based Tree and Sign Inventory Management Maps with the collected data. Based on this success, Chesterfield decided to build a Pavement Inventory Management Map by converting the old CAD drawings and collecting new GPS points.

In 2004, the city acquired aerial photography and digitized the edges of street pavement, curbs, sidewalks, and other rights of way. Once this base layer was created, mapping technicians overlaid CAD drawings and captured individual slab edges, as well as the text coding of streets and street segments (see Figure 1). Technicians assigned code identifiers to the concrete slabs.

Figure 1. Aerial photo of a street in Chesterfield. Red points represent individual pavement slabs; the yellow box contains data related to the highlighted slab.