Zone Preparation
Zoning is quite simple and it includes the following steps:
First of all pick up the accident problem e.g. more number of crashes involving heavy vehicles, two wheelers or pedestrian, high dose of drugs or alcohol that effect driving or stretch forcing monotones driving etc. This further need detailed accident data from FIR, Road Inventory and other sources. The data should be complete and sufficient enough to produce stable maps. At least three to four years data should made be available for the purpose because more data shows more better clusters of accident locations helpful in establishing zones.
Second the available data of accidents can be mapped manually or by a computerised mapping system often called as Geographic Information System (GIS). Computerised mapping is obviously more efficient in making the correct location of each event.
The GIS permits the analysis of full range of variables appearing in FIR Data, Road Inventory Data and other streams of data. It establishes a link among different streams of data pertaining to accident. These data records are to be entered in computer with the location information. There after the maps can be created to show the crashes not only of target groups but also of various subgroups e.g. early morning accidents or accidents at intersections. Separate maps are needed to display different subsets of data or different colour /symbol scheme could be adopted to show type of accidents.
Defining Zones
A visual examination of map will show whether accident crashes of interest clusters in some way in an area of city. If the clustering is not apparent i.e. map shows that target-groups events are randomly spreaded than problem may not be zoneable i.e. percentage of addressable problem is less than the percentage of land area covered. On the other hand if clustering is apparent with some dispersion it will show a some kind of pattern.
To identify zones it is necessary to provide some qualification to the concern zone. Some initial shape or pattern should be selected for zones and also fix some number of accidents that must fall in that area i.e. defined as zone. In establishing the pattern search should be made first for circular zones than for linear zones there after other patterns.
Search for circular zones
Experts says that accidents occur more frequently in a radius around some place e.g. around some work place, residential place, hospitals, schools or intersection. For study purpose accidents occurring within a radius of one or two kilometer will be a manageable area where safety improvements programs can be initiated. The circular zone must be characterised by minimum number of accidents; this rating will make it enable a deserving order zone to process safety improvement programs. The rate depends upon the size of sample of number of reported accidents available, how many accidents cluster and overall land area of concern covered. The number of accidents in a zone is simply an indicator where as clustering of accidents is more of high concern.
Search for linear zones
The safety improvements put their concentration along a road segment where accidents occur more frequently, which may be a part of circular zone. The GIS helps out in displaying those locations both on single strip of roadway as well as in circular zone. A manageable length for road segment and number of minimum accidents over a period of time must be allocated to make that linear zone ordered linear zone for safety improvement programs.
Final pattern of zones
With the aid of GIS map shows different pattern of interest where these pattern may be contiguous or scattered. When the contiguous zones overlap each other they are of more importance and demand high concentration. It may be possible when two circular zones having high number of accidents at periphery they can be clubbed with other zones and a new pattern can be created. It may be better to add or delete few locations to keep neighborhood zone intact. Boundaries may be revised to a square or rectangular area to generate better impact of safety improvement programs.
Ordering of zones
After establishing of circular, linear zones restructure the same if required to fall in some order. Finally for all the zones percentage of accident problem addressed and land area is required to be calculated in order to program coverage efficiency. If the ratio of percent of problem addressed to the percent of land area covered in the zone is much less than the defined zone may need to be re-examined. If efficiency ratio is high e.g. 60% of accidents of interest in 20% of concerned, land area will definitely demand for safety improvement measures. If the ratio is not going to be high that area may be studied as a non-zoneable area.
Zones Utilisation
- Once the zones are finalised in some order they are required to evaluated to access accident problem in depth through FIR and Inventory details etc. The evaluation should bring out limitation pertaining to driver, pedestrian, trees, medians, intersections, road furniture and inadequate lighting etc.
- Situation permitting collision need to be highlighted e.g. vehicles are too close to pedestrians when making right or left turn.
- Negative behaviour of driver or pedestrians or cyclist or other road users need to be examined with more importance.
- The high risk factors which effect the safety of pedestrians or other road users such as high speed, inadequate timing or operation of signal are need to be examine thoroughly.
High the value of these factors increases the likelihood that an accident will occur. The conclusions from zone evaluation need to be strengthened by on site analysis, observation and discussion with the people in defined area. Once the zones are identified and ordered with their problems marked as necessary for improvement than only relevant safety improvement measure (engineering, enforcement and public education & information) are require to be carried out.
Conclusion
The zoning application is not limited to one particular problem. In reality any highway safety problem, which can be described by the geographic location of occurrence will be a good exercise for zoning. The above strategy could be applied to all type of vehicle crashes, roadway maintenance activities and pedestrian safety etc. In fact zoning can potentially be applied to any highway problem that has a mappable target measure and could benefit from more efficient safety improvement program deployment.