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The procedures for determining the values of the AMFs for intersections (AMF10 through AMF14) are described in this section. The values of the geometric and traffic control variables needed to determine the AMFs are found in Intersection Geometric and Traffic Control Data. In all cases, the values for the AMFs for minor leg YIELD-controlled intersections are the same as for minor STOP-controlled intersections.
The AMF for intersection skew angle (AMF10) is defined as follows:
For a three-leg intersection with minor-road STOP-control, the value of AMF10 is:
where:
For a four-leg intersection with minor-road STOP-control, the value of AMF10 is:
If the skew angle for a four-leg intersection with minor-road STOP-control differs for the two minor legs, AMF10 is computed separately for each minor leg and the results averaged.
For a four-leg signalized intersection or an all-way STOP-controlled intersection, the value of AMF10 is 1.00.
The value of AMF11 for an intersection with all-way STOP control is 0.53. For all other intersections, the value of AMF11 is 1.00.
The values of the AMF for left-turn lanes (AMF12) on one or more major legs to an intersection is specified in Table 10., Accident Modification Factors for Installation of Left-turn Lanes on the Major Legs to Intersections. If there are no left-turn lanes on any major legs to the intersection, the value of AMF12 is 1.00. These AMFs are based upon the research documented in Report No. FHWA-RD-02-089, Safety Effectiveness of Intersection Left- and Right-Turn Lanes. The values in this table are from the judgement of an expert panel combining results from several sources.
| Intersection type |
Intersection traffic control |
One approach (leg) on which left-turn lanes installed |
Both approaches (legs) on which left-turn lanes installed |
| Three-leg intersection |
STOP control |
0.56 |
N/A |
| Three-leg intersection |
Signal control |
0.85 |
N/A |
| Four-leg intersection |
STOP control |
0.72 |
0.52 |
| Four-leg intersection |
Signal control |
0.82 |
0.67 |
Note that three-leg, signal-control intersections are not modeled by CPM.
The value of the AMF for right-turn lanes (AMF13) on one or more major legs to an intersection is specified in Table 11., Accident Modification Factors for Installation of Right-turn Lanes on the Major Legs to Intersections. If there are no right-turn lanes on any major leg to the intersection, the value of AMF13 is 1.00. These AMFs are based upon the research documented in Report No. FHWA-RD-02-089, Safety Effectiveness of Intersection Left- and Right-Turn Lanes.
| Intersection type |
Intersection traffic control |
One approach (leg) on which right-turn lanes are installed |
Both approaches (legs) on which right-turn lanes are installed |
| Three-leg intersection |
STOP control |
0.86 |
N/A |
| Three-leg intersection |
Signal control |
0.96 |
N/A |
| Four-leg intersection |
STOP control |
0.86 |
0.74 |
| Four-leg intersection |
Signal control |
0.96 |
0.92 |
Note that three-leg, signal-control intersections are not modeled by CPM.
The value of the AMF for llimited intersection sight distance (AMF14) at three- and four-leg intersections with minor leg STOP control is specified in Table 12., Accident Modification Factors for Intersection Sight Distance Limitations in Quadrants of Three-Leg and Four-Leg Intersections with Minor STOP Control. For four-leg signalized intersections and all-way STOP-controlled intersections, the value of AMF14 is 1.00.
| Number of quadrants with limited intersection sight distance |
Accident Modification Factor (AMF14) |
| 0 |
1.00 |
| 1 |
1.05 |
| 2 |
1.10 |
| 3 |
1.15 |
| 4 |
1.20 |
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