SAFETY ANALYSIS OF DRIVEWAY CHARACTERISTICS IN SOUTH CAROLINA USING GIS. Wayne A. Sarasua Kweku Brown

Transcription

1 SAFETY ANALYSIS OF DRIVEWAY CHARACTERISTICS IN SOUTH CAROLINA USING GIS Wayne A. Sarasua Kweku Brown

2 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

3 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

4 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

5 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.

6 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

7 Data Collection Procedures and Data Summary

8 30 Preliminary Corridors

9 SC Geocoded Crashes

10 Rear-end and angle crashes on US 25 in Greenville, SC for 2010 (left) and 2012 (right)

11 Symbol Table Driveway Related Crash Angle Crash Rear-end Crash

12 Greenville US 25 Length - 66 Driveway Crashes Rank 2 Rear End Angle 693 Clusters 9

13 Greenville US 25

14 Greenville SC 146 Length 13.9 Driveway Crashes Rank 3 Rear End 676 Angle 373 Clusters 20

15 Greenville SC 146

16 Greenville SC 146

17 Greenwood US 25

18 Richland US 1 Length 22.0 Driveway Crashes Rank 1 Rear End 1270 Angle Clusters - 30

19 Richland US 1

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22 Before and After Results

23 Richland US 176

24 Final 11 Corridors COUNTY ROUTE TYPE ROUTE NUMBER LENGTH (MILES) 3 YEAR DRIVEWAY AVG RANK DRIVEWAY CRASHES Richland US Greenville US Greenville SC Richland US Lexington US Horry US Spartanburg SC Greenville US York US Berkeley US Florence US

25 Map of 11 Corridors

26 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

27 Sample Driveway with Attributes

28 Driveway Spacing

29 Skew Angles

30 Safety Analysis

31 Right In Right Out Buffers

32 Full Access Buffers

33 Proximity Analysis Average Distance from Reported Route by Year Average Distance (FT) Route US 1, Richland US 25, Greenville SC 146, Greenville US 176, Richland US 1, Lexington

34 Buffers with Crash Overlay

35 Annual Crash Frequency by Driveway Class

36 Annual Crash Frequency Full Access vs Right-in, Right-out

37 Negative Binomial Estimation Results for Crashes per Driveway

38 Negative Binomial Estimation Results for Crashes per Driveway Variables Estimate Std. Error z-value p-value (Intercept) e < 2e-16 D_Spacing e D_Width e < 2e-16 N_Entry_Ln e RaisedMedian e D_Class e < 2e-16 D_Class e e-08 D_Control e e-14 Ln(AADT) e < 2e-16 SpeedLimit e FAorRIRO e

39 Crash Modification Factors Variables CMF 95% Confidence Bounds Median (1 for raised, 0 for all others) D_Class4 (High Turnover) D_Class5 (High Turnover) D_Control (Signalized) FAorRIRO (Full Access or Right-in-right-out)

40 Crash Modification Functions

41 Crash Modification Functions Driveway Width CMF DW DW a -DW b

42 Crash Modification Function

43 Crash Modification Function

44 Safety Performance Function

45 Crash Modifications Function

46 Corner Crash Analysis

47 Corner Clearance Annual crash frequency 0 to 150 feet from an intersection vs crash frequency 150 feet to 300 feet Distance from Intersection US 1 Richland US 25 Greenville SC 146 Greenville US 176 Richland SC 9 Spartanburg US 17 Berkeley # of driveways HP 2012 Crashes Crash frequency 0-150ft ft 0-150ft ft 0-150ft ft

48 Other Project Components Waiver Analysis Operational Analysis Economic and Benefit Cost Analysis

49 Recommendations for SCDOT ARMS

50 Sample Specific Changes to ARMS

51 Findings & Conclusions

52 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.

53 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.

54 Research Golden Nuggets for Practical Application (cont.) 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.

55 Thank you! Questions?