August 27


Reader Question:

Dear Mike,

I am a Traffic Engineer based in Karachi, Pakistan and a graduate of Michigan State.  We have a large up-scale residential colony with commercial centers. There are an estimated 20,000 plots in the colony with about 60% of the houses constructed.  There has been a request from the authority to consider converting some streets to one-way streets to better manage the traffic flow. 

This is a separate authority within the city with an area of 9,500 acres. Nearly 6,000 acres is built-up/saturated. A couple of the major streets of the network have already been made one-way. Total road network is 155 km (excluding 40′ wide and narrower streets). This includes roads with 60′ row up to 120′ row. Key entry/exit points have traffic up to 90,000 vpd, so they are very busy.

 Generally, the trend has been to go the opposite way, but are there any guidelines to see through this type of analysis?


My Response:

You are correct – the current trend is to move away from one-way streets and several communities have converted one-way pairs back to two-ways (my hometown of Minneapolis, MN went through this process about five years ago).  Two-way streets provide more flexibility and the general thinking is that they are friendlier to pedestrians and bicyclists.

I don’t know of any guidelines, but I think this would be a straightforward modeling exercise.  To fully identify the benefits of converting from two-way streets to one-way pairs, I think you’d need to:

  1. Collect existing data (preferably peak hour turning movements at key intersections, but at a minimum daily traffic volumes)
  2. Forecast what traffic will be when the remaining 40% of houses are built.
  3. Perform a capacity analysis (Vistro or Synchro based Highway Capacity Manual methodology) of those forecasts with the existing network with the fully built out traffic volume forecasts.
  4. Perform the same analyses with the network converted to one-way pairs.
  5. Compare the delay results of your two study scenarios.  Maybe there are just one or two key corridors that should be converted, while leaving everything else two-way.  I wouldn’t convert to one-way unless there were clear operational benefits that offset the downgrading of the multi-modal system.

Rehan also mentioned doing a crash analysis, which is probably a good idea if there are any issues that could nudge the “engineering judgment” in one direction or another.

Additional Thoughts on the Situation?

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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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