As part of a roadway improvement project, a rail crossing with flashing lights a
ID: 1710214 • Letter: A
Question
As part of a roadway improvement project, a rail crossing with flashing lights and sound signals is now being considered for the installation of automatic gates. The intersection crash history is averaging 20 total crashes per year, with 50% of related to the grade crossing. What will be the high and low likely reduction in the expected average crash frequency at the 95^th confidence level? Note the tables provide AMFs (an old draft of the HSM before they were changed to CMFs) Given Information: Existing roadway = rural two-lane road Crossing type = at-grade crossing Existing traffic control = flashing lights and sound signalsExplanation / Answer
Average Crashing per year at the Intersection = 20 per Year
Average Crashing Per Year at grade crossing i.e. 50% of total avg. =0.5x20 = 10/year
Reduction in crashing due to the Modification = (AMF) x Crashing per year
S.No.
Treatment
Initial Average Crashing
AMF
Standard error
Average Reduced
Crashing (X)
Confidence interval factor i.e 95 th
(1.96 X standard error)
Lower limit
Upper limit
1.
Install flashing lights and sound signals.
10
0.5
0.05
5
4.90
5.10
2.
Install automatic gates at crossing that
previously has passive traffic control.
5
0.33
0.09
1.65
1.47
1.83
3.
Install automatic gates at crossing that
previously had flashing lights and sound signals.
5
0.55
0.09
2.75
2.57
2.93
Average Crashing per year at the Intersection = 20 per Year
Average Crashing Per Year at grade crossing i.e. 50% of total avg. =0.5x20 = 10/year
Reduction in crashing due to the Modification = (AMF) x Crashing per year
S.No.
Treatment
Initial Average Crashing
AMF
Standard error
Average Reduced
Crashing (X)
Confidence interval factor i.e 95 th
(1.96 X standard error)
Lower limit
Upper limit
1.
Install flashing lights and sound signals.
10
0.5
0.05
5
4.90
5.10
2.
Install automatic gates at crossing that
previously has passive traffic control.
5
0.33
0.09
1.65
1.47
1.83
3.
Install automatic gates at crossing that
previously had flashing lights and sound signals.
5
0.55
0.09
2.75
2.57
2.93
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