Delaware 2006 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 2006 - 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 2003 and December 2005 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 statistically significantly greater than other similar roadways. For FY 2006, eighty-one locations were identified with a Critical Ratio greater than 1.0 and with three or more crashes within a 0.3 mile segment. A summary of the top 5 percent or four 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 crashes during the three-year study period revealed that 1.6 percent of fatal crashes and 4.8 percent of incapacitating injury crashes (or 3.8 percent of the total fatal and incapacitating injury crashes) occurred on suburban and municipal roadways. These roadways represent 34 percent of public roadway mileage. These crashes represent a small proportion of the total reported crashes reported throughout the state. Therefore, 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 Rate[1] | Potential or Proposed Improvements | Estimated Costs | Implementation Impediments |
|---|---|---|---|---|---|---|
| 1 | Hollyville Road (Road 305) at Mount Joy Road (Road 297) | 6.25 | 4.56 | Recently converted intersection from two-way to four-way stop control and removed crops and brush to improve corner sight distance. | $3,000 | None |
| 2 | Sand Hill Road (Road 319) near Rudd Road (Road 245) | 6.00 | 4.20 | Pavement surface was grooved in Fall 2005 to address wet weather crashes. Police enforcement is needed to address crashes caused by speeding. Potentially install raised pavement markings, delineators, advisory speed limit signs, and oversized curve warning signs to provide improved warning to motorists. | $5,000 | None |
| 3 | SR 1/US 113 at SR 9 and Kitts Hummock Road | 5.60 | 0.28 | Interchange currently in design to improve safety, preserve traffic capacity, and security for traffic entering Dover Air Force Base. | $12 million | No construction funding available. |
| 4 | US 13 at Paradise Alley Road (Road 287) | 5.22 | 0.47 | Potentially install an intersection control beacon (ICB) or hazard identification beacons (HIB) on US 13 with the Cross Road signs and upgrade signing and pavement markings. | $50,000 | None |
[1] Rate per Million Vehicle Miles Traveled (includes fatal and incapacitating injury crashes only)
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 crashes in roadway type[2] (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:
CRt = 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 statistically significantly greater than other similar roadways.
[2] For the 5 Percent Report, only fatal and incapacitating injury crashes are included.
