An accident occurred in which Driver 1 turned right from Post Road onto the eastbound lane of Route 460. Driver 2 was approaching this same intersection on Route 460, traveling east. Driver 2 swerved left to avoid hitting Driver 1, passing driver 1, and then stopping ahead of driver 1. Driver 1 passed the now stopped car of Driver 2 and pulled onto the shoulder off Route 360 east of Driver 2. Police arrived, and details for the accident were gathered.
Site Evidence
Driver 1’s car stopped a distance of 325 feet east of Post Road. Driver 1 stopped 50 feet east of Driver 2’s car. Driver 1’s car was a 2018 Jeep Grand Cherokee. Driver 2’s car was a 2018 Honda Fit.
Road conditions were dry. The road at this point is straight and level. No other cars were affected by the incident.
Driver Statements
Driver 1’s version: Driver 1 said he pulled out while Driver 2 was still some distance west of the intersection and that Driver 1 had accelerated to 50 MPH before Driver 2 swerved around him, evidently going well over the speed limit for Route 460, which is 60 MPH. Had Driver 2 not been speeding, he would have been able to slow and not swerve.
Driver 2’s version: Driver 2 said he was driving at 60 MPH, and Driver 1 pulled onto Route 460 when Driver 2 was only two car lengths from the intersection, forcing Driver 2 to swerve to avoid a collision. Driver 1 had barely started to accelerate and could not have been going 50 MPH when Driver 2 had to swerve around Driver 1. He started his swerve one car length behind Driver 1 and started to stop when he was one car length in front of Driver 1.
Additional Information:
· Based on a test of acceleration for all vehicles, a 2018 Jeep Grand Cherokee model can accelerate from zero to 60 MPH in 8.6 seconds.
· Based on tests of stopping distance, the Honda Fit can brake from 60 MPH to a stop in a distance of 131 feet.
· Consider a car length to be 15 feet.
It may be useful to do calculations in units of feet/second rather than miles/ hour. The conversion rate is 1 MPH = 1.467 ft/s so 50 mph = 73.3 ft/s and 60 mph = 88 ft/s.
1. Calculate the acceleration rate of the Jeep Grand Cherokee in feet/second/second or ft/s2.
2. Calculate how much time Driver 1 would take to reach 50 mph (73.3 ft/s) while accelerating at the rate determined in part 1. Remember that the acceleration rate represents how much the speed increases each second.
3. Next we need to figure out how far the car would travel while accelerating at this rate (part 1) for this amount of time (part 2). You have the data you need. Find the right equation and solve.
4. Now it’s time to evaluate the two driver's stories. If driver 2 passed driver 1 after driver 1 accelerated to 50 mph (73.3 ft/s), he would have to have started his deceleration farther down the road from the intersection than the distance calculated in part 3. Add the estimated stopping distance for driver 2’s car to the result of part 3 above. What is this distance?
5. Which driver’s account do you believe and why?
