With the release of Fast and Furious 7 this past weekend, and considering the ridiculous vehicle stunts seen therein, (no spoilers necessary – just go watch the trailer) we’ve started thinking about vehicle stunts from famous movies of the past and wondering how plausible they are. One of my favorite stunt scenes is from Live Free or Die Hard (2007), when traffic is re-directed from both ends of a tunnel in an attempt to ruin John McClane and Matt Farrell’s days. The scene culminates in McClane somehow driving his car up an improvised ramp (it’s actually a tollbooth but hey – everyone gets that one wrong at some point) and jumping it into a helicopter while throwing himself free at the last second.
We’ll ignore any discussion over whether or not this helicopter stunt would have been possible. (Although Reel Physics does address this one in their video) I’m more interested in the circumstances surrounding the tunnel and whether or not everything inside would have been able to actually happen. We invite you to watch this high quality cell-phone recorded version and get up to speed on the scene. Let’s break it down:
- McClane and Farrell (henceforth M&F) enter the tunnel to escape a helicopter that is following them
- The tunnels are opened from both directions
- The lights are turned off
- A car swerves to avoid a crash, and in doing so gets t-boned by an oncoming car, sending it flying directly at M&F – which they subsequently avoid in a lucky turn of events.
- The aforementioned flying car hits a truck, which causes it to accelerate (?) and drive right towards M&F, because life is just hard that way. (Spoiler: They also avoid this one.)
We’ll go over these events one by one.
Entering a Tunnel to Escape the Helicopter
Right off the bat we’re going to have to start suspending our disbelief. Fortunately for you, you just watched a decelerating car drive through a metal structure and still have enough momentum to carry it 30 feet into the air to smash a helicopter, so you seem to have that covered. For now we’ll just pretend that a gridlocked city would still have enough space for a car to outmaneuver a helicopter and not get shot to pieces. In a convenient turn of events, the open space on the roads suddenly becomes filled with cars ready to follow into the tunnel after McClane.
Tunnels are opened from both directions
This is where things get fun. It’s easy to brush this off as “Hollywood Garbage,” but it turns out it’s actually pretty easy to hack traffic lights. We don’t know the extent to which all traffic signals are networked, but if it a team at the university of Michigan could hack 100 networked lights, we’re prepared to believe that tunnel signals are part of that same vulnerable network. A recent push for new “Smart” traffic lights would also mean that city infrastructure will become even more connected and have even more potential risks of cyber attacks from angry megalomaniacs.
All in all, we shouldn’t necessarily assume that there wouldn’t be a fail-safe in place to prevent both sides of a tunnel being opened at the same time.
Lights are turned off
Hopefully you’re the sort of smart person who turns on your lights when you’re going through tunnels. If you’re not, hopefully then at least you’re the type of person who turns his lights on when you’re driving and you can’t see anything outside of your car. If you are not, I recommend you exchange your car for a comfortable pair of shoes. Or you could just be like a normal, functioning member of society and not continue racing into a tunnel when you can’t see anything. Up to you.
Assuming tunnel lights are also networked like traffic lights and streetlights, this scenario is also a possibility – although we don’t know the specific possibility of changing these lights from the inside of a truck like this guy does.
Flying Cars and… Spontaneous Truck Acceleration?
Maybe we shouldn’t be so surprised by the truck accelerating after being hit. After all – we’ve already seen that unintended acceleration is a real problem with some cars. The driver’s foot could have stuck on the pedal, or something could have shifted within the truck to force the gas pedal down. Instead of focusing on that, let’s examine the likelihood that a car could even become airborne in a T-bone crash. We know that T-bones can definitely result in dangerous rollovers, but how easy is it to get a car into the air?
This video shows a Formula One car being hit and flipping completely off the ground, but these cars are going much faster than a normal car would, in addition to weighing a little less than half as much as a regular car, so it takes a little less force to make it airborne. After a little research (looking at T-bone crash videos on youtube) it looks like although cars can flip as a result of being T-boned, it might take some extreme circumstances to launch a car into the air with such force.
In our situation, the car that swerves to avoid a crash (Vehicle 1) and ends up perpendicular to the road may be still be traveling forward at ~20 mph at the moment of impact (according to very rough estimates gathered from this video), and we’ll assume a (probably high) speed of 40mph from the car (Vehicle 2) breaking to avoid hitting vehicle 1. We’ll also assume that Vehicle 2 provides a perfect, 30 degree angled ramp, but to account for friction, we’ll shave of a measly 20 mph of the car’s initial velocity. With these two cars moving toward each other, we can assume the horizontal velocity of 40mph for vehicle 1 approaching a ramp. (Note: Guessing is a terrible way of determining numbers for math problems regarding car crashes. If you want smarter answers, I suggest Randall Munroe’s blog on hypothetical situations.)
Because the internet is awesome, I can plug the aforementioned numbers into a trajectory calculator that I found, which shows that the car will be airborne for about 1.7 seconds, reaching a maximum height of around 12 feet. This is a little less extreme than what we see in the movie – I estimate that the maximum height of the car in the movie is around 25 feet the time of flight is around 3 seconds.
Using our handy calculator again, the initial velocity of the car would have to be about 55mph at the time it leaves the ramp. Is the whole scenario unlikely? Definitely. Keep in mind though that this stunt was a practical stunt – meaning that the cars involved were real and not CGI. The vehicle spinning through the air was attached by cable to a crane that pulled it forward. Would it have been able to happen without the assistance of a crane? Let’s just leave it at “possibly.”
Regardless of whether or not the stunt hit the mark in terms of plausibility, even a car that’s airborne for 2 seconds that reaches a height of 12 feet will travel for 80 feet before hitting the ground and rolling even further. If you’re one of those people who drives in a tunnel with no headlights when the lights start turning off, please try to avoid being in the same city as Bruce Willis.