Safety Analysis of Driveway Characteristics in South Carolina Using GIS

Abstract:

The overall goal of this project is to enhance SCDOT’s current access management practices resulting in a reduction in crashes, injuries, and fatalities on South Carolina roadways as well as improved traffic flow. 

Findings & Conclusions

  • Problems result when developers circumvent standard adherence through the waiver process
  • Comprehensive driveway database critical to analysis
  • Precise crash data is critical to analysis
  • Makes it possible to associate crashes with driveways
  • Can also facilitate corridor level and even statewide analysis with more robust results
  • Reading crash narratives is time consuming and it is sometimes difficult to associate a crash with a particular driveway
  • Use junction type with caution.  Many driveway related crashes may be overlooked.

Research Golden Nuggets for Practical Application

  • Research Findings: Raised medians can cut driveway related crashes in half (CMF of 0.49).
  • Right-in, right-out driveways eliminate 3 conflict points that are the most critical with respect to crash severity and RIRO driveways have less than half the crash frequency of full access driveways.
  • Reducing access point density improves roadway capacity and reduces need for new capacity improvements.
  • Driveways within 150’ of a an intersection have nearly twice the crash frequency of driveways 150’ to 300’ from an intersection.
  • Better access policies result in lower crash severity, not just frequency.
  • Approval of access waivers from adherence to good design practice often result in higher crash frequency.
  • High turnover land use such as fast food restaurants have much higher crash frequency over other land uses such as small businesses.

Wayne A. Sarasua, Ph.D., P.E.

**Won an award from AASHTO High Value Research Project

YouTube video presentation will be linked at a later date.

Slide List:

Wayne A. Sarasua, Ph.D., P.E.

Glenn Department of Civil Engineering, Clemson University

  1. Overall Goal
  • The overall goal of this project is to enhance SCDOT’s current access management practices resulting in a reduction in crashes, injuries, and fatalities on South Carolina roadways as well as improved traffic flow
  1. Literature Review

  Access Management studies generally fall into three categories :

  • Impacts on Safety
    • Median
    • Access point density
    • Sight distance
    • Intersection & Interchange
    • Turn prohibition
  • Impacts on Traffic Operations
    • Level of service
    • Capacity
  • Impacts on Residents and Business

Literature Review –

  • Access point density:
  • Schultz et al., “Safety impacts of access management techniques in Utah, ” (2007) evaluated the safety performance of arterials in which access management techniques have been implemented. They concluded that the relationship between access points per mile and crash rate has a positive correlation in Utah.
  • Frawley and Eisele, “Crash analyses of raised medians and driveway density: How access management makes communities safer,” (2004) completed an evaluation of 11 case studies in Texas and Oklahoma and showed that implementing raised medians and performing driveway consolidation would reduce the potential number of conflicts points along roadways.
  • Conclusion: reducing access point density reduces crash rates, reduces speed differential between vehicles, enhances operation and could improve roadway capacity and reduce need of new capacity improvement

Literature Review –

  • Medians:
  • Gattis et al., “Roadway median treatments,” (2010) examined relationships among crash rates and different types of median (None with occasional left turn lanes, two-way left-turn lane, Raised, Depressed) of roadways in Arkansas. They concluded that raised or depressed median yield the lowest crash rates.
  • Mauga and Kaseko (2010) evaluated and quantified the impact of types of medians, including raised medians and two-way-left-turn-lanes on traffic safety in the midblock sections. The results showed that segments with a raised median had lowered the crash rate by 23% compared to segments with a TWLTL.
  • Schultz et al., “Safety benefits of median installations in Utah,” (2012) analyzed safety at locations where raised medians are installed. They concluded  that raised medians significantly reduce crash frequency and severity.
  • Frawley, “Raised median economic impact and safety research findings: Application for Cooper street,” (2010) studied the benefit of converting a two-way left turn lane to a raised median for particular locations in Bryan, Temple and Tyler, Texas.  The benefits include lower crash frequency, fewer crashes involving left-turns, no migration of crashes to intersections, very few U-turn crashes, and fewer severe crashes.
  • Conclusion:  Raised medians reduce crash frequency and severity  with no migration of crashes to intersections.  Traffic operations are improved.

A Methodology for Determining the Economic Impacts of Raised Medians

  • William L. Eisele, P.E., and William E. Frawley, AICP (TTI 1999)
  • Business owners who were present before, during, and after the median installation felt that their regular customers continued to use their businesses
  • In contrast, those businesses that were interviewed prior to the installation of the raised median thought their customers would be less likely to continue to use their businesses 
  • Perceptions appear worse than reality

Data Collection Procedure and Data Summary

  1. 30 Preliminary Corridors
  2. SC Geocoded Crashes
  3. Problems with hand-held GPS data
  • Several crash records were missing either longitude or latitude or both
  • Some crash records were in state plane coordinates, not latitude and longitude
  • Several crash records were in Decimal Degrees (DD),  not DMS
  • Some crash records had their longitude and latitude values swapped
  • Most of the latitude values did not include a negative sign
  • Several coordinates were recorded with insufficient precision by one or two decimal places
  • Some crash records had spaces and letters as part of the coordinate entry
  • Some coordinates included additional zeroes to make up for the insufficient precision
  • Some crash records had erroneous coordinate values
  1. Percent of Crash Data by Geocoded Category and by Year
  2. Rear-end and angle crashes on US 25 in Greenville, SC for 2010 (left) and 2012 (right)
  3. Symbol Table
  4. Greenville US 25
  • Length - 66
  • Driveway Crashes - 309
  • Rank – 2
  • Rear End - 880
  • Angle – 693
  • Clusters – 9
  1. Greenville US 25
  2. Greenville SC 146
  • Length – 13.9
  • Driveway Crashes - 294
  • Rank – 3
  • Rear End – 676
  • Angle – 373
  • Clusters – 20
  1. Greenville SC 146
  2. Greenwood US 25
  3. Richland US 1
    • Length – 22.0
    • Driveway Crashes - 353
    • Rank – 1
    • Rear End – 1270
    • Angle - 715 
    • Clusters - 30
  4. Richland US 1
  • Before and After Results
  1. Richland US 176
  2. Final 11 Corridors
  3. Map of 11 Corridors
  4. Corridor Analysis Data Collection Process
  • Geometric Data were collected for selected corridors in three categories
  • Segment
    • intersection to intersection
  • Driveway
  • Intersection
  • All data were geocoded into ArcGIS
  1. Sample Driveway with Attributes
  2. Driveway Spacing
  3. Skew Angles
  4. Safety Analysis
  5. Right In Right Out Buffers
  6. Full Access Buffers
  7. Proximity Analysis
  8. Average Distance from Reported Route by Year
  9. Buffers with Crash Overlay
  10. Annual Crash Frequency
  11. by Driveway Class
  12. Annual Crash Frequency
  13. Full Access vs Right-in, Right-out
  14. Negative Binomial Estimation Results for Crashes per Driveway
  15. Negative Binomial Estimation Results for Crashes per Driveway
  16. Crash Modification Factors
  17. Crash Modification Functions
  18. Safety Performance Function
  19. Crash Modifications Function
  20. Corner Crash Analysis
  21. Corner Clearance
  22. Annual crash frequency 0 to 150 feet from an intersection vs crash frequency
  23. 150 feet to 300 feet
  24. Other Project Components
  • Waiver Analysis
  • Operational Analysis
  • Economic and Benefit Cost Analysis
  1. Recommendations for SCDOT ARMS
  2. Sample Specific Changes to ARMS
  3. Findings & Conclusions
  • Problems result when developers circumvent standard adherence through the waiver process
  • Comprehensive driveway database critical to analysis
  • Precise crash data is critical to analysis
  • Makes it possible to associate crashes with driveways
  • Can also facilitate corridor level and even statewide analysis with more robust results
  • Reading crash narratives is time consuming and it is sometimes difficult to associate a crash with a particular driveway
  • Use junction type with caution.  Many driveway related crashes may be overlooked.

Research Golden Nuggets for Practical Application

  • Research Findings: Raised medians can cut driveway related crashes in half (CMF of 0.49).
  • Right-in, right-out driveways eliminate 3 conflict points that are the most critical with respect to crash severity and RIRO driveways have less than half the crash frequency of full access driveways.
  • Reducing access point density improves roadway capacity and reduces need for new capacity improvements.
  • Driveways within 150’ of a an intersection have nearly twice the crash frequency of driveways 150’ to 300’ from an intersection.
  • Better access policies result in lower crash severity, not just frequency.
  •  Approval of access waivers from adherence to good design practice often result in higher crash frequency.
  • High turnover land use such as fast food restaurants have much higher crash frequency over other land uses such as small businesses.
  • Posted on: Tue, 04/25/2017 - 14:41
  • By: fbroen
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