Delaware 2007 Five Percent Report
This report is in response to the Federal requirement that each state describe at least 5 percent of its locations currently exhibiting the most severe highway safety needs, in accordance with Sections 148(c)(1)(D) and 148(g)(3)(A), of Title 23, United States Code. Each state's report is to include potential remedies to the hazardous locations identified; estimated costs of the remedies; and impediments to implementation of the remedies other than costs. The reports included on this web site represent a variety of methods utilized and various degrees of road coverage. Therefore, this report cannot be compared with the other reports included on this Web site.
Protection from Discovery and Admission into Evidence—Under 23 U.S.C. 148(g)(4) information collected or compiled for any purpose directly relating to this report shall not be subject to discovery or admitted into evidence in a Federal or State court proceeding or considered for other purposes in any action for damages arising from any occurrence at a location identified or addressed in the reports. |
Additional information, including the specific legislative requirements, can be found in the guidance provided by the Federal Highway Administration,
http://safety.fhwa.dot.gov/safetealu/fiveguidance.htm.
Delaware Department of Transportation
Fiscal Year 2007 - 5 Percent Report
In response to Section 148(c)(1)(D) of Title 23, United States Code, the Delaware Department of Transportation has prepared this "5 Percent Report" describing 5 percent of their public road locations exhibiting the most severe safety needs.
Methodology Used to Identify Locations
DelDOT uses the Critical Ratio methodology (see Attachment 1) to identify high crash locations for all Highway Safety Improvement Program components. For the 5 Percent Report, fatal and incapacitating injury crashes during the three year study period between January 2004 and December 2006 were included in the analysis.
The Critical Ratios of locations with three or more fatal or incapacitating injury crashes within a 0.3 mile segment during a three-year study period are ranked in descending order. Critical Ratios equal to or greater than 1.0 indicate a location with a crash rate that is significantly greater than other similar roadways. For FY 2007, eighty-six locations were identified with a Critical Ratio greater than 1.0 and with three or more fatal or incapacitating injury crashes within a 0.3 mile segment. A summary of the top 5 percent or five locations is shown in Table 1.
Extent of Public Road Coverage and Schedule for Upgrading Crash System to Full Coverage
Crash data for all public roadways within Delaware is collected by Delaware State Police and transferred to DelDOT for inclusion in their Safety Data Management (SDM) system. The Critical Ratio method that DelDOT uses to identify high crash locations requires crashes to be located on a linear reference milepoint system. Although all crashes statewide are included in DelDOT's SDM, suburban and municipal roadways are not included in DelDOT's linear reference milepoint system and are therefore not included in the Critical Ratio analysis used to identify high crash locations.
A review of statewide crash data on all roadways revealed that a very small percentage of fatal and incapacitating injury crashes occurred on suburban and municipal roadways although these roadways represent 34 percent of public roadway mileage. DelDOT does not currently have any plans to expand their linear reference milepoint system to include suburban and municipal roadways.
Contact Information
Randall Grunden
DelDOT HSIP Manager
randall.grunden@state.de.us
(302) 659-2025
169 Brick Store Landing Road
Smyrna, DE 19977
Table 1 - Highway Segments Exhibiting the Most Severe Safety Needs
| Site | Location | Critical Ratio | Crash Rate1 | Potential or Proposed Improvements | Estimated Costs | Implementation Impediments |
|---|---|---|---|---|---|---|
| 1 | SR 30 at Zoar Road | 8.56 | 5.48 | Studied as part of the 2007 High Risk Rural Roads Program – Site 13. Recommended improvements include the installation of an intersection control beacon (ICB) and signing and striping improvements, which will be constructed in Fall 2007. | $98,000 | None; currently in Construction. |
| 2 | SR 16/Hickman Road near University Road | 5.98 | 3.41 | Roadway was resurfaced in Summer 2006 and raised pavement markings (RPMs) were installed. Proposed improvements include the installation of chevrons and upgraded warning signs to oversized fluorescent yellow warning signs and trimming trees to improve warning for motorists. These improvements will be implemented in Fall 2007. | $2,000 | None |
| 3 | SR 1 at SR 9 and Kitts Hummock Road | 5.40 | 0.27 | An interchange is proposed to improve safety, preserve traffic capacity, and increase security for traffic entering Dover Air Force Base. | $13.1 million | None; Construction scheduled for Summer 2008. |
| 4 | U.S. 113 from south of SR 20 to north of Sheep Pen Road/Bark Pond Road | 5.27 | 0.58 | Studied as part of the 2005 and 2006 Highway Safety Improvement Programs. Closure of the median opening at U.S. 113 at Sheep Pen Road/Bark Pond Road is proposed to eliminate conflict points. Lengthening of the acceleration lane for eastbound SR 20 right-turning vehicles onto southbound U.S. 113 is proposed. | $500,000 | None; currently in Project Development. |
| 5 | Sand Hill Road near Rudd Road | 5.17 | 4.29 | Pavement surface was grooved in Fall 2005 to address wet weather crashes. Additionally, this location was studied as part of the 2007 High Risk Rural Road Program. Signing and striping improvements were recommended, including the installation of advisory speed limit signs on the approaches to the curves and chevron alignment warning signs within the curves. These improvements were installed in Summer 2007. | $900 | None |
Attachment 1
Critical Ratio Methodology for Identifying High Crash Locations
DelDOT uses the Critical Ratio methodology to identify high crash locations for all Highway Safety Improvement Program components. The Critical Ratio method (also know as the Rate Quality Control Method) uses a statistical test to determine whether the crash rate at a particular location is significantly higher than a predetermined average crash rate for locations of similar characteristics. The statistical tests are based on the commonly accepted assumption that the occurrence of crashes approximates the Poisson distribution. In this method, the Crash Rate (CR) at a given location is compared to a Critical Crash Rate (CCR), which is based on the average statewide crash rate for the roadway type.
The first step in the Critical Ratio method is to determine Average Crash Rates for different roadway types throughout the state. All roadways included in DelDOT's linear reference milepoint system are divided into functional classifications, urban and rural categories, and two-lane, multi-lane divided, and multi-lane undivided categories. The total of these different roadway types is twenty-nine (29). After these 29 different roadway types are defined, Average Crash Rates (ACR) for each roadway type are calculated using the following formula:
where:
ACRt = Average Crash Rate for roadway type "t" per million vehicle-miles traveled
Nt = Total number of fatal and incapacitating injury crashes in roadway type (3 year period)
Lt = Total length in miles of roadway type
AADTt = Average Annual Daily Traffic of roadway type (3 year average)
1095 = Number of days in 3-year period
Critical Crash Rates (CCR) for each 0.30 mile segment of roadway are then calculated using the following formula:
where:
ACRt = Average Crash Rate for Roadway Type
AADTs = Average Annual Daily Traffic of each roadway section
K = 1.645 (95% Confidence Level)
1095 = Number of days in 3-year period
Critical Crash Rates (CCR) are a statistical test of the significance of the calculated crash rate for each section of roadway. Their values vary as the AADT changes.
A Crash Rate (CR) for any chosen road section is then computed using the following formula:
where:
CRs = Crash Rate for roadway section
Ns = Total number of crashes in section (3 year period)
Ls = Length of section (0.30 miles)
AADTs = Average Annual Daily Traffic in section (3 year average)
1095 = Number of days in 3-year period
Lastly, the Critical Ratios are calculated as follows:
Critical Ratios equal to or greater than 1.0 indicate a location with a crash rate that is significantly greater than other similar roadways.
