August 28, 2000 |
2000-R-0771 | |
HIGH ACCIDENT LOCATIONS ON I-95 | ||
By: James J. Fazzalaro, Principal Research Analyst | ||
You asked us to identify the most dangerous locations on I-95, particularly with respect to accidents that produce injuries or fatalities.
SUMMARY
While identifying specific locations along I-95 as more dangerous than others is somewhat subjective, we have used an accident database the Department of Transportation (DOT) maintains for identifying state highway locations that are candidates for accident reduction strategies to assist in this response. We used accident index data from this and a related report to show relative accident experience for 161 locations along I-95 for the three years from 1995 through 1997, the most recent period for which the data has been compiled. This information relates the total accident and injury and fatality accident experience of these locations to locations elsewhere on the state highway system.
Based on this information, we identified seven locations—two in Darien and one each in Stamford, Bridgeport, Norwalk, West Haven, and New Haven—that exhibited both total accident and injury or fatality producing accident experience during this period which put them among the top 10 on I-95. The index for the I-91/RT 34 interchange in New Haven ranked sixth for total accidents and eleventh for injury/fatality accidents. Three locations—one in Stratford, between Barnum and Bridgeport avenues, and two in the Stonington-North Stonington area at the RT 2 and RT 49 interchanges ranked in the top 10 for injury/fatality accidents, although they ranked much lower for total accidents.
Considering the highway as a whole, the highest hazard areas of I-95 according to this analysis would appear to be the sections from Exit 8 in Stamford to the Noroton Avenue interchange in Darien; from just after the RT 136 interchange in Darien to the East Avenue interchange in Norwalk; from just after the RT 33 interchange to the Sherwood Island Connector in Westport; the RT 8 interchange in Bridgeport; from the Campbell Avenue interchange in West Haven to Exit 49 in New Haven; the section between the Branford Connector and Cedar Street and the Leetes Island Road interchange in Branford; the section between Exits 84 and 85 in New London; the RT 2 interchange in Stonington; and the section between this and the RT 49 interchange in North Stonington.
IDENTIFYING HIGH ACCIDENT LOCATIONS
Determining what locations on I-95 could be considered the most “dangerous” requires some subjectivity. Although the total number of accidents that occur at a particular place can be an indicator of how dangerous it is, these totals are directly affected by the volume of traffic using the location and other factors. Thus, it is possible that two similar locations, such as two interchanges, might experience the same number of accidents over a particular period, but one is really more dangerous than the other because the exposure factors such as traffic volume are quite different for the two.
Therefore, we did not base this analysis on only a count of the total accidents that occur at various locations along I-95. Instead, we took accident information from a DOT database known as the Traffic Accident Surveillance Report (TASR). DOT compiles this accident information for the purpose of identifying state highway locations that provide the greatest potential for accident reduction. The list is called the Suggested List of Surveillance Study sites or SLOSS.
The TASR consists of a database into which DOT puts accident frequency and location information, traffic volume, facility classification and related data for thousands of locations on state highways. The TASR is updated annually and contains data for a three-year period for statistical validity. Thus, it essentially provides a rolling three-year “snapshot” of where accidents occur.
The most recent TASR information is the basis for this report. This is for the three years from 1995 through 1997. DOT will be including 1998 accident data in the next TASR update, but because of the time required for his process, it cannot be expected for some time. Therefore, this analysis covers I-95 locations for the 1995-97 period.
To address the question of injury and fatality producing accidents, we asked DOT for additional information it compiles in another database called the Injury and Fatality Traffic Accident Surveillance Report. This provides information in the same format as the TASR, but it does not separate fatality from injury producing accidents, nor can it distinguish by injury severity. Even with this limitation, these two databases provided adequate information to respond to your question.
EVALUATION METHODOLOGY
The TASR contains location identification, classification, accident frequency, traffic volume, vehicle miles, and other information for 161 locations along the entire length of I-95 for the 1995-1997 period. (Similar information is compiled for all other state highways as well.) DOT determines an average accident rate for various roadway types according to formulas that account for factors such as road section length, vehicle and mileage volumes, the overall time period, and the total number of similar type locations throughout the state highway system. By determining an average accident rate for each road type, comparisons can be made more easily between dissimilar facilities.
DOT then develops the “critical accident rate” for each location as the minimum criterion for determining what locations should be included on the SLOSS. The critical accident rate is a function of time, section length, traffic volume, and the system average accident rate for the category of highway being tested for accident abnormality. Locations where actual accident rates exceed critical accident rates are considered SLOSS sites.
In making this determination, DOT calculates the ratio of a location's actual accident rate and its critical accident rate. Any location that has 15 or more accidents and where the actual accident rate exceeds the critical rate is eligible for inclusion on SLOSS. Locations are rank-ordered by the size of the ratio. In effect, this means that locations for which this ratio is 1.0 or less are experiencing relatively normal or below normal accident experience while locations with ratios above 1.0 have abnormal accident experience over the study period. The more the ratio exceeds the 1.0 index number, in effect, the more abnormal the location's accident history compared to similar locations throughout the state highway system.
We used this index as the basis for presenting the accident information you requested for I-95. The locations identified in the tables and charts in this report are differentiated according to this index ratio and not by the number of accidents. The total number of accidents does affect a location's critical accident rate, but not to the exclusion of other factors.
HIGH HAZARD LOCATIONS ON I-95
Based on this analysis, the 10 locations on I-95 with the highest ratios for total accidents and thus, apparently the most abnormally high accident experience for the 1995-1997 period were, in descending order:
1. Darien—Between the RT 136 and U.S. 1 interchanges (2.97)
2. Darien—Between the Brookside Drive and Noroton Avenue interchanges (2.04)
3. New Haven—Between Exits 48 and 49 (2.01)
4. Norwalk—At the East Avenue interchange (1.99)
5. West Haven—Between the RT 122 and the RT 10/SR 745 (Boulevard) interchanges (1.84)
6. New Haven—At the I-91/RT 34 interchange (1.72)
7. Bridgeport—At the RT 8 interchange (1.68)
8. Branford—Between the SR 794 (Branford Connector) and SR 740 (Cedar Street) interchanges (1.67)
9. Fairfield—Between the U.S. 1 and U.S. 1/SR732 interchanges (1.52)
10. Stamford—At Exit 8 interchange (1.47)
With respect to accidents that produced injuries or fatalities the 10 I-95 locations with the highest index ratios for 1995-1997, and thus the most abnormally high accident experience were, in descending order:
1. Norwalk—At the East Avenue interchange (1.89)
2. West Haven—Between the RT 122 and RT 10/SR 745 (Boulevard) interchanges (1.82)
3. Stamford—At the Exit 8 interchange (1.69)
4. Bridgeport—At the RT 8 interchange (1.62)
5. Stonington—At the RT 2/SR 617 interchange (Exit 92) (1.59)
6. New Haven—Between Exits 48 and 49 (1.58)
7. Darien—Between the Brookside Drive and Noroton avenue interchanges (1.41)
8. North Stonington—Between the RT 2 and RT 49 interchanges (1.41)
9. Stratford—Between the U.S. 1 (Barnum Avenue) and U.S. 1 (Bridgeport Avenue) interchanges (1.40)
10. Darien—Between the RT 136 and U.S. 1 interchanges.
Seven locations appear on both of the lists, although in different rankings. Of particular note is the fact that two adjacent locations, the RT 2/SR 617 interchange in Stonington and the road segment between that exit and the adjacent exit for RT 49 in North Stonington have an injury accident index that is significantly above their total accident index. This implies that the accidents occurring at these locations are producing injuries or fatalities in a greater proportion than for typically similar locations on the rest of the state highway system. Exit 8 in Stamford is a similar location with an injury/fatality index of 1.69 and a total accident index of 1.47. Another Stamford location, at the U.S. 1 (Main Street) interchange has an injury/fatality accident index of 1.37 and a total accident index of 1.22. The Exit 6 interchange area in Stamford also produced a higher injury/fatality accident index than total accident index, but both are below the threshold level of 1.0 that is indicative of abnormal experience relative to similar locations on the state highway system.
When the data for all of I-95 are examined as a whole, several areas emerge that could be considered as the most dangerous. One such area begins at Exit 8 in Stamford and runs to the Noroton Avenue interchange in Darien. Four of the five locations in this stretch have injury/fatality and total accident ratios that exceed the 1.0 index level indicative of abnormal experience relative to similar locations elsewhere on the highway system. The location that does not exceed this level is the Brookside Drive interchange.
A second stretch that exhibits an abnormally high accident experience begins in the area after the RT 136 interchange in Darien and runs approximately to the East Avenue interchange in Norwalk. All six of the locations in this segment have both injury/fatality and total accident ratios above the 1.0 level. The section in Westport running from just after the RT 33 interchange to the Sherwood Island Connector also exhibits accident ratios above 1.0.
As noted previously, the RT 8 interchange in Bridgeport shows indexes in both areas well above 1.5. With the exception of two locations in Stratford, the next section with abnormal accident experience does not occur until the Campbell Avenue interchange in West Haven. High accident ratios are evident for most of the New Haven area from just after the RT 122 interchange to Exit 49.
Except for spikes for two locations in Branford, injury/fatality accident ratios for most locations stay fairly well below the 1.0 index level until the western end of I-95. A spike occurs for the location between Exits 84 and 85 in New London and again for the RT 2 interchange in Stonington and the section from the RT 2 interchange to the RT 49 interchange in North Stonington.
Appendix 1 of this report displays the accident index information graphically in four sections for the areas from Greenwich through Fairfield, Bridgeport through East Haven, Branford through Old Saybrook, and Old Lyme through North Stonington. Locations with accident ratios above the 1.0 level are identified individually.
Appendix 2 presents the TASR and Injury and Fatal Traffic Accident Surveillance Report data in tabular form with all locations identified.
JF:ro
APPENDIX 1
I-95 Accidents by Location
The four charts that follow show the accident index for all 161 locations along I-95 for which data is maintained in the DOT Traffic Accident Surveillance Report. The index is for accidents occurring from 1995 through 1997.
Two data points are shown for each location. The graph lines and data points shown in BLUE are for all accidents. The graph lines and data points shown in RED are for accidents producing injuries or fatalities.
The individual locations are identified as either interchanges or segments of highway between interchanges. Interchange data points are shown in outline.
Road segments between interchanges are shown as solid shapes.
The first chart shows I-95 from Greenwich through Fairfield.
The second chart shows I-95 from Bridgeport through East Haven.
The third chart shows I-95 from Branford through Old Saybrook.
The fourth chart shows I-95 from Old Lyme through North Stonington.
Any locations for which the accident index is above the 1.0 level (indicated by the heavy black line) had accident experience that would be considered abnormally high for like locations on the state highway system.
APPENDIX 2
Accident and Index Data Table for I-95
The information in the table identifies all 161 locations in the DOT Traffic Accident Surveillance Report and provides the total number of accidents and injury or fatality producing accidents at each location for the 1995-1997 period. Each location's accident index is shown next to the number of accidents.
Each location's identification number (first column) corresponds to a number on the bottom of one of the four charts in Appendix 1. For example, location #6 identifies the road section from the Arch Street interchange to the Indian Field Road interchange in Greenwich. Location #13 is the Exit 8 interchange in Stamford. These would be found on the first chart above the numbers 6 and 13 respectively.
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