Friday, 1 March 2013

Well, That's Just The Way The Mercedes Bends

So I'm cruising down Albert street. Ahead of me, I can barely see the buildings' high rooftops through the thick falling snow. It was reminiscent of one of those apocalyptic movie scenes where the rising smoke tells the tale of what must have been a great battle scene in some urban concrete jungle. People are walking a little slower. Traffic is beginning to slow. Just another snowstorm in Ottawa.

I dread these days.

By the halfway point of my shift, people are tired. I'm sitting in traffic, the bus is stuffy with humidity and the heat needed to keep the fog off the front window, and the later I become the more people I have to pick up. Soon the bus becomes stuffed with standing people. The crowd grows to the point where I can no longer pick anyone up, but I still have to stop on every platform because the line of buses has now become a series of small leaps forward followed by long periods of staring at brake lights.

I can see the disdain in the eyes of those who knock on my front door flashing their passes at me. "You can fit ONE more" they seem to be saying, with a throw of the hands and a turn of the heel.

It's not a fun day to be a bus driver.

On the bus however, is a different story. People are talking about what is going on, how late they are, and how grateful they are that we are not one of the many buses stuck in the snow. They all ask the same question. "How is it to drive one of these things in the snow?"

The articulated bus is a very difficult animal to drive in snow. Traction is terrible, acceleration is unpredictable, braking is inconsistent, and the articulation point is poorly designed.

Traction with these vehicles is difficult to master. The buses are rear wheel drive, which means that the trailer pushes the tractor along on a pivot. There are two problems that occur when we lose traction. First, the drive wheels break traction, then the bus articulates and the center wheels break traction. From a driver's standpoint, you don't even get the benefit of "road feel" from the bus. The trailer is in another postal code, and once you feel the sliding of the center axle, it's too late. This is why you see these buses stuck with the trailer ultimately out of line with the rest of the bus like one of those giant "Check Your Route" check marks.
Once the bus is bent, it is game over.

It really doesn't matter what kind of tires you are wearing, or how much salt you throw under the drive wheels. When the bus bends, there is simply too much friction resisting acceleration, and the torque applied to the drive wheels will seek the easiest release and simply continue to articulate the bus on the pivot. 

With the bus bent, the center axle receives this power at an angle and the tires simply cannot maintain lateral traction. Add to that the upwards force that inevitably comes with pushing on a stationary object, and you might as well put crazy carpets under the center wheels.

This is not a tire issue.

If this company is to continue ordering articulated buses, it needs to insist on a basic engineering solution to what really hinders the traction on these buses.

Lock the turntable.

The pivot is the problem. If these buses had a way for the driver to lock the pivot temporarily while he/she is in the beginning stages of getting stuck, then the overwhelming majority of these buses would be able to wiggle out of a traction issue the same way a 40 foot straight bus can.

This wont solve our current issues. The only improvement we could make with this current crop of articulated buses is an improvement in driver skill. But having said that, the traction issues are far and beyond what can be reasonably solved through training. Simply put, these vehicles are not designed for deep snow.

The double deckers however, manufactured in Britain of all places and not in Winnipeg like the New Flyer articulated buses, are wonderful in the snow. The traction control kicks in on the first sign of wheel slip, and the driver can turn that feature off should the need arise to rock the bus back and forth in a snow pile. The buses have two rear axles which seems to limit fishtailing, and the weight over the front wheels seems to aid in steering. 

I'm really warming up to these double deckers. 

Solid. Predictable. And, very wet inside. Just like Britain.

  

1 comment:

  1. Thanks very much for the details. I don't think I realized before this that the drive wheels are in the very back of those articulated beasts. That...just does not make sense.

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