Study Details
Study Title: Identifying Crash Distributions and Prone Locations by Lane Groups at Freeway Diverge Areas
Authors: Chen et al.
Publication Date:JAN, 2011
Abstract: In this study, the overall and severe crashes for four exit ramp types at freeway diverge areas were compared by crash distribution and location. Crash contributing factors were identified, including exit ramp types, geometric design features, traffic conditions, and crash related attributes. Exit ramp types are defined by the number of lanes exiting freeways and the lane balance theory which is determined by AASHTO. Four typical exit ramp types were considered: 1) one-lane exit with lane-balanced design (Type 1); 2) one-lane exit with lane-unbalanced design (Type 2); 3) two-lane exit with lane-balanced design (Type 3); and 4) two-lane exit with lane-unbalanced design (Type 4). Lanes are further classified as Exit/Drop Lane-Group, Impact Lane-Group, and Interior Lane-Group. Proportionality tests were employed to compare the crash distributions on different lanes. The results indicate that lane-balanced designs (Type 1 and Type 3) have a statistically significant higher percentage of severe crashes on the impact lane-group than that of lane unbalanced designs (Type 2 and Type 4). As for the interior lane-group, Type 4 ramps have a statistically significant higher percentage of severe crashes than the other types. In addition, ordered probit models were developed for overall crashes and severe crashes by one-lane exits and two-lane exits, respectively. Model results suggest that more crashes occurred on the exit/drop lane-group for the lane-unbalanced designs (Type 2, Type 4) and more severe crashes occurred on the interior lane-group for the lane-unbalanced designs. The study would expectedly help engineers have a better understanding of crash locations for different exit types, thus enabling appropriate countermeasures.
Study Citation: Chen, H., Wang, Z., Lu, J., and Pontoriero, D., "Identifying Crash Distributions and Prone Locations by Lane Groups at Freeway Diverge Areas." Presented at the 90th Meeting of the Transportation Research Board, Paper 11-0955, Washington, D.C., (2011).
CMFs Associated With This Study
Category: Interchange design
Countermeasure: Change length of deceleration lane on one-lane freeway exit ramp from X to Y miles
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
 |  | All | All | Principal Arterial Other Freeways and Expressways |
Countermeasure: Change number of lanes on freeway with one-lane exit from X to Y
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| | All | All | Principal Arterial Other Freeways and Expressways |
Countermeasure: Change number of lanes on freeway with two-lane exit from X to Y
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
|  | All | All | Principal Arterial Other Freeways and Expressways |
| | All | K,A | Principal Arterial Other Freeways and Expressways |
Countermeasure: Convert balanced lane configuration to unbalanced lane configuration at one-lane exit
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 1.43 | -43 | | All | All | Principal Arterial Other Freeways and Expressways |
| 0.98 | 1.9 | | All | K,A | Principal Arterial Other Freeways and Expressways |
Countermeasure: Convert balanced lane configuration to unbalanced lane configuration at two-lane exit
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 1.23 | -22.9 | | All | All | Principal Arterial Other Freeways and Expressways |
| 0.97 | 3.4 | | All | K,A | Principal Arterial Other Freeways and Expressways |
Category:Shoulder treatments
Countermeasure: Paved right shoulder vs. other right shoulder type on freeway ramp
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.81 | 19.2 | | All | All | Principal Arterial Other Freeways and Expressways |
| 0.9 | 9.7 | | All | K,A | Principal Arterial Other Freeways and Expressways |
Category:Speed management
Countermeasure: Change freeway speed limit from X to Y mph
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| | All | K,A | Principal Arterial Interstate |
