On Road Accidents and Knudsen Diffusion

On Road Accidents and Knudsen Diffusion


This afternoon I witnessed a road accident involving a motorcycle. Again.

Sunday. I was driving on an almost empty lane. The counter lane's traffic was snail-paced. Through the rear view mirror of my car, I noticed a speeding motorbike at least a hundred meters behind. I was running 40; the bike was running faster. A little later, another motorbike appeared in the mirror. The two bikes were driving as if on a race. The first bike then sped past my legal speed, changed lane and was now in front of me. But a van on the counter lane some 50 meters before me signaled and started to do a left turn.  The first bike, trying to avoid the van, changed lane again, but into the counter lane. Too late, the bike driver must not have seen the cab that showed up when the van cleared the counter lane. The cab tried to change lane, to the right, to avoid the bike, but the bike still hit the cab. The man on the bike was tossed into the air. He's still lucky, there were no other vehicles on the counter lane that could have run him over. But the bike was a real wreck.

The second bike almost hit the van that turned left. On avoiding the van, the bike almost hit the gutter.

I didn't know how to react. The man on the bike was still alive. He actually managed to stand up and walked toward the wreck. The cab and the van froze but I didn't see the drivers come out as I drove away from the accident scene. I would just imagine the traffic congestion it could have caused.

While driving away, a well-known model for diffusion in solids popped on my head. I was thinking of these motorbikes as diffusing molecules that would flow through any available interstices. These daredevil molecules didn't realize that their "mean free path" is actually greater the size of the interstices. So, their tendency to hit the walls of these interstices is high. Chemical engineers and chemical engineering students should know what I mean. Knudsen diffusion, anyone? But here, the extra challenge is that the walls of interstices are non-stationary. By "mean free path" I don't mean the average distance traveled between collisions but the average distance of traveled on changing direction based on the "drunkard's path model."

I and my crazy thoughts agree that if these daredevils know Knudsen diffusion and Drunkard's Path Model, they could avoid accidents. This is also know as "follow the rules."

These thoughts were erased when another thought popped on my head: the real scare I had when I had a flat tire while running on 70 on the Buendia flyover. I must have run over a sharp object that could have caused the loud bang of the right rear tire of my car that resulting in mild tremor to the inside of the car. It happened last night.