A simple design solution in roadwork

Here's a design problem with a simple solution.

Here’s a design problem with a simple solution.

The city is repaving our road.  In prelude to that, they’re replacing the curbs and sidewalks.  I saw this out my front window today.  As I watched them go at it, I noticed a very significant problem in the system consisting of the curb-layer (the yellow machine to the right), the cement truck, and the workers.

Can you figure it out?

The problems might be more obvious if I had a clip of the action rather than just a still, so let me describe what happens.  The yellow machine is guided by an operator (off the right side of the shot) and follows a metal guidewire you can just barely see against the black truck tires.  The machine runs at a very slow and very steady pace.  It consumes concrete and actually lays a perfectly formed curb out the back.

For the machine to operate properly, it needs a constant supply of concrete, which is delivered by the mixer truck. There’s a worker watching the concrete pour out of the truck, down the truck’s chute, and into a reservoir at the front of the curb-laying machine.  That worker has three jobs: (1) make sure the truck’s chute is not clogging; (2) make sure that the machine’s reservoir is not overflowing or starving for concrete, and (3) making sure the truck keeps its position as the machine moves at its constant pace.  All this has to be done without getting chewed up by any of the heavy machinery he is within inches of for relatively long periods at a time without a break.  He’s also standing in a shallow ditch that’s very uneven, so he has to watch his footing too.

The driver’s got a hard job too.  He’s got to keep an eye on his side rear-view mirror, so that he can see the worker on the street signal him to speed up, slow down, go, or stop.  These signals come from the worker irregularly and, therefore, unexpectedly from the perspective of the driver.  The driver also has to keep his eyes on the road.  This is a residential street; kids live here, kids who might do stupid things when they see a “mighty machine.”  The driver can’t really see the machine behind him at all, let alone the flow of concrete down the chute, so he’s completely dependent on the worker to know what’s going on back there.  He also has to drive right along the edge of the ditch into which the curb will go.  If he drives off the road and into the ditch, work will have to stop while other workers repair the ditch (the size and depth of the ditch is very important for installing a good curb).

Is this really the best we can do?

I think there’s a number of very easy and economical modifications that can be done here that would help matters tremendously.

As usual, the problems arise from the interfaces between the truck, the mixer, the driver, and the worker.  There’s nothing particularly wrong with the cement truck; it’s designed for flexibility, to be used in a variety of different situations.  Jack of all trades, as it were, but master of none.  The machine is clearly designed to take advantage of how typical mixers are arranged.  And yet, when these two products interact, there are problems.

The machine moves at a constant, fixed rate.  The mixer has a huge range of rates of motion.  The mixer steers with great precision over a relatively narrow range.  The mixer has a huge range of steering, but isn’t as precise because, in general, it doesn’t need to be.  The machine can’t be seen (well, if at all) from the cab of the mixer, but it has to be in back of the mixer to accept the cement coming down the truck’s chute.  All this means that the driver and the worker have a lot to do.

The reservoir on the machine cannot be made much bigger than it is without also adding a stirring mechanism to keep the cement’s consistency correct.  Adding a churner to the machine makes it more complex, harder to maintain, costlier, and more prone to breakdown.

One might consider attaching the machine to the back of the mixer and letting the mixer pull the machine along.  But now the mixer has to be able to follow the guidewire very precisely, and it was never designed to do that.

Designing an entirely new class of machine that combines mixer and machine doesn’t eliminate the need of a mixer to bring the concrete to the site, and would have a very small market; probably too small to justify its design and development.

We could go all “high tech:” add some sort of cruise control to the truck that’s keyed to the movement of the machine.  We’d need some sort of electronic communications system between the two.  Again we have the problem of increased complexity.  And we still have the problem of the driver having to guide the machine along the guidewire more precisely than the truck and its driver can do.

But as a wise man said: “The more they overthink the plumbing, the easier it is to stop up the drain.”

My solution is not really mine.  it’s based on a project done by a student in my graduate design course. (Yes, Michael, I’m talking about you.)  His project involved finding a simple way to help farmers align tractors with modular machine elements that attach to the front of the tractor.  In his experience, this required a driver and at least one other person to “spot” the location and orientation of the mating points at the front of the tractor and relay that information to the driver of the tractor, who would have to line the tractor up to mate with the element.  His solution involved placing colourful tape and a couple of mirrors in key locations on the machine elements and the tractor.  All the driver had to do was keep the coloured tape properly aligned as he approached the machine element.  He’d actually implemented the change on his family’s farm, and it had worked beautifully.

Here’s the first part of my soluton.  Before starting a run, the machine is first positioned properly; then the truck lines up at the right distance and position in front of the machine.  Next, two differently coloured circles on flexible arms are attached, one to the machine and the other to the mixer.  They are aligned so that the truck driver sees them aligned in his side rear-view mirror.  Cross hairs on the mirror tell the driver where to position his head to watch the coloured circles’ positions correctly.  Then the machine gets under way.  The driver watches the circles.  If the one circle becomes visible inside the other, that means he’s too far from the machine and needs to slow down; if the other is visible within the one, then he’s too close and needs to speed up.  Now the driver has direct, immediate feedback on his location available any time he glances at his mirror, which eliminates many of the problems with the existing arrangement.

It’s also a ridiculously cheap and simple solution that adds virtually no complexity to the system; also, it’s a purely “mechanical” solution that avoids delicate and finicky electronics.

We might even consider adding another, detachable mirror to be used on the mixer, instead of the permanently attached side mirror.  This detachable mirror can be positioned so that the driver doesn’t have to turn his head as much to see the coloured circles behind him.  This will probably lessen neck and eye strain for the driver, as well as giving him more chance to keep an eye out for obstacles to the mixer itself.  One might also add another mirror to give the mixer’s driver a better view of the ditch along the edge of which he has to drive.  I would expect this solution will decrease stress on the workers, decrease mistakes and accidents, and possibly increase productivity by letting both the machine and mixer move faster (assuming that is even possible for the machine).

We’re not done yet, though.  There’s still the worker walking along, in the ditch, at the back of the mixer / front of the machine.  That worker has to keep the chute on the mixer and the reservoir of the machine working and clear of obstructions.  His job is already easier because he doesn’t have to gauge the separation between the truck and the mixer, and communicate with the mixer’s driver.  But we can do more for him.

Based on my observations of the machine, I think it would be possible to attach a removable outrider seat on the machine, somewhere near the left front corner of the machine.  The worker can now sit in this seat and use a pole and water hose to make sure both the chute and reservoir are clear.  Sitting on the left side he’d also be in view of the driver, adding and extra “back-up” mechanism for the driver to know what’s going on behind him.  The seat not only reduces back strain on the worker; it’s also no longer possible for him to trip and fall as he walks in the ditch.  This lets the worker focus more, but with less overall cognitive load, on the tasks he’s really there to perform.

Adding a removable seat to the front of the machine will be more expensive than the mirrors and coloured circles for the mixer’s driver, but I would expect it to be minimal compared to the cost of the machine itself.  Again, it’s a simple solution that adds minimal complexity, lowers worker risk, and has at least the potential to increase productivity.

So there you have it, folks; my solution for laying curbs faster, safer, and easier.

What do you think?


One thought on “A simple design solution in roadwork

  1. Pingback: New design case study | Filippo A. Salustri, PhD, PEng

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