Probability Scale Quantification of Fault Trees 1 in 10 Frequent 1 in 100 Probable TOP CRASH AT CRASH Probability = 0.001 or 1 in 1000 EVENT MAIN ROAD 1 in 1000 Occasional JUNCTION If 6000 cars use the side road every year, then it is expected that 6-7 crashes per year 1 in 10000 Remote may occur 1 in 100000 Improbable AND 1 in 1 m Extremely Remote CAR AT MAIN SIDE ROAD ROAD CAR FAILS TO JUNCTION STOP P=0.01 OR P=0.131 SIDE ROAD SIDE ROAD CAR CAR DRIVER DRIVER COULD DID NOT STOP NOT STOP P=0.12 OR P=0.011 OR DRIVING DRIVER VISION ROAD TOO BRAKE TYRES TOO FAST TOO ILL OBSCURED SLIPPERY FAILURE WORN P=0.1 P=0.01 P=0.01 P=0.01 P=0.001 P=0.0001 -Option Build an Overpass Install a stoplight and grading Cost $10 million $150,000 Risk Impacted Impac't'It Car at Main Road Reduces the probability of "Car Junction at Main Road Junction" from 0.01 to 0 Car at Main Road Reduces the probability of "Car Junction at Main Road Junction" from 0.01 to 0.003 Reduces probability of "Driving Install Speed Bumps $20,000 Driving too fast too fast" from 0.1 to 0.03 Install Radar Speed $10,000 Driving too fast Reduces probability of "Driving Display too fast" from 0.1 to 0.06 Install additional $2,000 Driving too fast Reduces probability of "Driving Speed Limit signs too fast" from 0.1 to 0.08