Investigation of Weather Conditions and Their Relationship to Crashes

Background This project will investigate weather conditions and associated safety by analyzing start times of precipitation (e.g.,snow, blowing snow with reduced visibilities, or even freezing rain} and the time of crashes on Nebraska Highways. The number of crashes and fatalities related to weather (Figure 1.} are relatively large when compared to other weather phenomena (e.g.,tornadoes, hurricanes, etc.}. Questions such as how long had it be precipitating before a crash occurred are relevant to improving highway safety. Crash reports lack detailed weather information; this may be remedied by incorporating weather observations from National Weather Service (NWS} locations close to crash locations. It is also important to study whether there were NWS weather advisories, watches or warnings during or preceding a crash. There is literature regarding times of day and crashes with increases during the morning and evening commutes, however,there is not a lot of information dealing with weather conditions duringthose commute times. For example, on Nebraska roads is it more likely to be involved in a crash in a winter weather condition during the morning or evening commute? Analysis of snow accumulation at selected observation location sindicates that there is a higher probability of accumulating snow for the morning rush hour than the evening rush period (Figure 2}. Does the start time of precipitation help indicate when crashes will occur? Will crashes increase if precipitation starts several hours before the peak traffic hour? Preliminary analysis indicates that the number of crashes goes down with greater snowfall amount. More crashes occur with light snowfall amounts than with heavier amounts. However, severity of the crashes seems to increase with increasing snowfall amounts. A climatological look of Nebraska winter weather for the past 10 years has recently been completed for NDOT. The winter weather severity index, NEWINS, classifies daily events by the weather conditions. NEWINS values range for 1to 6 where category 1 is a marginal winter storm and category 6 is a severe event were heavy snow and blizzard like conditions may be expected with road closures and suspended operations by NDOT may have to be invoked during one of these events. Individual snowfall events have been classified by the 1-6 severity, however, the crash data have not been investigated using the NEWINS scale. How do crash occurrences relate to the severity level? Classifying crashes compared to the scale will a lso effect the maintenance operations. Understanding the occurrence of crashes and the weather conditions may change how maintenance is performed during events. One of the other outcomes of the NEWINS study was the importance of snowfall rate. Snowfall rate which is usually not forecasted by the NWS, is the amount of snowfall falling during a specific period of time. Many times if the rate of snowfall is low, the snow will melt on the road surface. It is when the rate becomes greater than the surface can melt does accumulation start to take place. While this proposed study cannot determine the accumulation of snow on road surfaces, because information on the road treatments (applied or residual) or road surface conditions (pavement temperature) are not well enough observed during a weather event, especially at a crash location. However, we will be able to investigate through NWS weather radar returns when the heaviest snow was occurring and how this might be associated with the timing or severity of a crash. Preliminary analysis also indicate that more crashes occur with greater snowfall rates (Figure 3). This needs to be further explored better determine the weather condition during the crash. The case study analysis will able to mine the weather data during the event, to derive the worst case scenarios taking place during crashes so that maintenance can treat the road surfaces. Objectives The main objective of this investigation is to correlate motor vehicle crash data to precise weather conditions associated with the time of the crash. We are limiting our investigation to when winter weather conditions could be a factor in the crash. This could include, snow fall resulting in snow covered roads, freezing rain causing icy conditions, low visibilities due to falling snow and/or high snowfall rates and strong wind speeds causing drifting snow onto the road surface. Statistical analyses can formulate what weather situation causes the greatest safety concerns, and what might be the appropriate maintenance response to those weather conditions. The crash data will be divided into fatalities/injuries and personal property damage. In addition, NWS forecasts will be analyzed before/during a crash to determine what weather information was available during the event.


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    • Status: Completed
    • Funding: $191,758.00
    • Sponsor Organizations:

      Nebraska Department of Transportation

      1500 Nebraska 2
      Lincoln, NE  United States  68502
    • Project Managers:

      Halsey, Lieska

    • Performing Organizations:

      University of Nebraska, Lincoln

      1400 R Street
      Lincoln, Nebraska  United States  68588
    • Principal Investigators:

      Anderson, Mark

    • Start Date: 20190701
    • Expected Completion Date: 20201231
    • Actual Completion Date: 20201231
    • USDOT Program: Transportation, Planning, Research, and Development

    Subject/Index Terms

    Filing Info

    • Accession Number: 01705674
    • Record Type: Research project
    • Source Agency: Nebraska Department of Transportation
    • Files: RiP, STATEDOT
    • Created Date: May 23 2019 3:35PM