March 18


Is the Client Always Right?

By Mike Spack

March 18, 2014

gravel truckA gravel mining operation is expanding in our region and they could have up to 18 trucks entering and then exiting their facility per hour.  The trucks all turn at a local road/state highway tee intersection (each are two lane roads, no turn lanes, side street is stop sign controlled).  We were hired to determine if the state highway intersection needed upgraded traffic control or turn lanes.

We did our weekday a.m. and p.m. peak hour traffic counts, did forecasts, and ran the capacity analysis.  Under all circumstances, the intersection will operate at Level of Service A with each movement operating at Level of Service B.  We even did a sensitivity analysis where we doubled the truck traffic at the intersection – worst movement degraded to Level of Service C.

The plant manager was surprised.  He was expecting to need turn lanes at this sleepy intersection (a few thousand vehicles a day on the state highway and almost no vehicles on the cross street).  I tried to explain that adding turn lanes would cost $50 to $100k at the intersection and that it might actually make things slightly less safe (larger intersection for the trucks to turn onto would mean they need larger gaps).

So he had a meeting with DOT staff that I couldn’t make and he came back to me – what about summer conditions where the traffic on the state highway could be heavier due to resort traffic.  The DOT had summer counts, so I factored up the through volumes 75% to match up with the summer volumes and ran the scenario with the doubled truck traffic.

Under this exaggerated situation, the worst movement in the a.m. peak hour was Level of Service C and the worst movement in the p.m. peak hour crawled into Level of Service E with 36 seconds/vehicle on the worst movement (overall, less than 4 seconds of delay per vehicle).

DOT staff jumped on this Level of Service E and are recommending a bypass lane and right turn lane be added to the intersection.  I get their position.  It’s hard to know which configuration is safer since we’re really playing at the margin.  Adding the turn lanes could be seen as a free upgrade to the highway system since the plant should cover that cost.

My first boss, Shelly Johnson, told me several times that we are consultants making recommendations.  We’re not responsible for implementing the solutions and you need to develop a certain detachment from your work if you’re going to survive as a consultant.

I believe I made the correct recommendation in this situation, but my client wanting turn lanes isn’t a terrible idea.  It’s his money and I need to let this one go…


  • Mike,
    Level of Service is not the only reason to install a left or right-turn lane. A turn lane can be installed due to safety concerns along the highway such as a vehicle rear ending one of the trucks. This is especially true for most highway conditions. Since this appears to be a relatively dirty operation, dust and dirt can build up on the back of the trucks/trailers such that the reflective lenses, lights, etc. are less effective than what we see with a sparkling clean truck. The plant manager may have had complaints from citizens, staff, his own truck drivers regarding near misses. So, I think this is actually a condition/situation that warrants other factors besides what pops out of a computer program.

  • Gilmer – I agree it is in the gray area and we should never just go with what a computer spits out. Mike

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    Mike Spack

    My mission is to help traffic engineers, transportation planners, and other transportation professionals improve our world.

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