Red Light, Green Light!
You’re a controller in a traffic operations centre in a large city. Your job is to use webcam streams to monitor busy intersections. When you see heavy congestion, you can change traffic lights to improve the situation. One day, you see a firetruck and an ambulance heading towards the same intersection from perpendicular directions. They will arrive at the traffic lights at the same time. What do you do?
This scenario was one of my favorites to close out an interview. While my colleagues rolled their eyes when I brought this one up, I found it useful to assess an applicant outside of the experience and technical skills we’d normally focus on for most of the interview. Full disclosure: I came across this scenario years ago. I don’t remember where I read it or even if I reproduced it correctly. And I didn’t search online for details before putting this blog together.
As far as I was concerned, there was no right answer. In all the years giving this oral exercise, I never had a candidate ask me an obvious question: Are the lights flashing on either of the vehicles? I’d watch to see how long it would take for the candidate to reply. Very subjective, but I wanted to see a delay of a few seconds while they think about the problem before articulating a response. Hopefully, they picked one or the other vehicle to prioritize at the lights. (I had candidates over the years say that they didn’t know what to do.) If they prioritized the ambulance, I’d respond with something like, “The fire truck could be on its way to an incident with multiple casualties. There’s likely only a single casualty in the ambulance. Are you sure it’s best to prioritize the ambulance?” If they prioritize the fire truck, I’d come back with, “A substantial number of calls for the fire service end in false alarms. Are you sure you want to prioritize the fire truck?” My response was to test their conviction in their answer – how well would they defend it? Would they consider the counterargument and change their answer? I’d watch for tone and what they said to assess whether they were open to other ideas, were defensive, or waffled when pressed.
Did the answers lead me to outstanding hires? Unfortunately, I have no idea. Like any interview question – even technical ones – the decision to proceed with an offer is founded on a subjective opinion. I did find over the years that presenting this scenario near the end of an interview helped close out the technical Q&A portion.
And how would I respond? I’d never considered what I’d say until I began writing this blog. My answer would be something along these lines.
Assuming that the lights are flashing on both vehicles, I’d change the traffic lights to give the firetruck the fastest passage through the intersection.
I’m sure the interviewer would ask why.
I don’t know the criticality of response time for these first responders. I guess I missed that memo during my training. So, I base my answer on what I do know. With 100% certainty, the firetruck is on the way to the incident; firetrucks don’t flash their lights returning to the station. It’s 50/50 with the ambulance. During the few seconds’ delay at a traffic light, if the ambulance is heading to a hospital, the victim is under the care of a paramedic in the vehicle. Some traffic accidents require the use of a Jaws of Life. Firefighters use this hydraulic rescue tool to extricate a victim from a vehicle. In these situations, the ambulance comes into the picture after the extrication.
If given a counterargument for why I might want to consider the ambulance to have priority, I’d respond politely with the following.
Thank you for that additional information. I suspect other factors also play into the time-criticality of a first-responder incident. I’d want to be better versed in the statistics to make an informed choice. My response today is based solely on what I can conclude.
Would my answer nail the job interview for me? I’m glad I’ll never know.
