Integration of GIS and Orthophoto to Enhance Road-Network Screening – A 3GR Approach



5 Implementation on Safety performance Function
The technique developed in this paper to enhance the street lighting database record is applied to the development of safety performance functions (SPFs). the SPFs, calibrated for two-lane rural highways under different lighting conditions. The SPFs calibrated for the raw data without any enhancement and for the data after enhancement. The results shows that the integration of GIS, orthophotos, and the road network database (e.g. collisions database, AADT, and intersection data) enhance the SPFs analysis.

The study how the method might affect road safety analysis, SPFs for two-lane rural highways (300 road segments with a total length 140 km) were calibrated before and after enhancing the data using the thesis technique. The thesis technique was also used to discover and resolve hidden problems in the data record.

The results were as follows:
  • 7 % of the raw data was subject to conflicts. The new technique was able to identify and correct 90% of the conflicting records.
  • 8 % of the raw data were unknown segments. The technique was able to identify 92 % of the unknown segments.
6 Summery, Conclusions and Recommendations

6.1 Summery
The integration of GIS, orthophotos and road network-screening database was implemented in this paper. Few researchers have worked in this field. The semi -automatic technique, which developed in this research, provides a tool that enables road safety agencies to verify illumination data in their databases and to fill in any gaps. The integration procedure improved the network-screening database.

The semi-automatic method successfully extracted the position of streetlight poles and identified whether road segment types were illuminated or not An important advantage of the semi-automatic method is that its application does not require users to have a strong remote sensing background or image processing skills.

The procedure resolved 90% of the data conflicts found in the data for illumination; and identified 92 % of the unknown segments (illuminated or not) for the targeted highways. The semi-automatic method is ideal for rural and semi-urban areas. The proposed technique is considered to be unique because it improves the data for illumination in the road database (enhancement illumination database is not covered adequately in the field of road safety).

However, the semi-automatic method may not work if high buildings or other obstructions cover the pole’s shadow. For this reason, the method is not recommended in downtown areas or close to high-rise buildings. Nevertheless, if the street poles are unobstructed, it may be possible to determine the segment type even if some poles cannot be located.

6.2 Conclusions
Many researches in road safety field wish to maximize their use of existing databases. Efficient and in-expensive solutions need to be found to check data and to fill gaps in the data. Data improvements and validation will have a direct effect on the quality of any analysis of the data.

The integration of GIS, orthophotos and databases can play a key role in improving the road network-screening database. The integration approach presented and discussed in this thesis offers a new tool to check and improve illumination data in the databases of road safety agencies. The technique can also help road safety agencies to extract additional features from road network data.

In this study, orthophoto images with 0.2m spatial resolutions were used to extract the pole type/positions and to identify the segment types and locations. High-resolution remote sensing images can be used to accomplish the same task, but it is recommended that remote sensing images with 1.0-metre resolution should be used to identify road segment types.

6.3 Recommendations
Orthophoto images can play a key role in extracting illumination data from the street network. Road agencies should give more attention to orthophotos images because the mages have considerable potential for supplying additional data about the road network.

High-resolution remote sensing images can be used to identify the segment type and to improve the street network database. Remote sensing images are widely available at a low cost, which will encourage road agencies to acquire them.

It is recommended that the technique proposed in this thesis should be used to check and examine intersections to identify which intersections are controlled by traffic signals. In addition, this technique can be used to improve collision data records for accidents involving fixed objects.

Illumination can improve road safety especially in rural areas. While it is not practical to illuminate all rural roads, hazardous segments should be identified and illuminated.

Road jurisdiction databases should also benefit from the integration of GIS and network-screening databases.

The integration of GIS, GSM, GPS and remote sensing (3GR) can help road safety analysts to improve the quality and accuracy of their analysis. It can help the road safety analyst to predict annual average daily Traffics (AADT), and vehicles miles travel (VMT). It can improve crashing data analysis and classification.

References
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