“You can’t squeeze ten pounds of sugar in a five pound bag”

Residents of Johns Creek have heard this quote on more than one occasion when it comes to issues relating to traffic.  This quote, unfortunately, suggest that we have twice the volume of traffic at our intersections than we can handle.

But, what if the volume at our intersections was not twice as much as they can currently handle?  What if they were only 9-13%% over the capacity today?  Could we make some minor changes that would yield major improvements?

While it has been very easy to dismiss options for improving traffic because of statements that really have nothing to do with improving the performance of our intersections(Ten pounds of sugar, Forsyth County Growth, road widenings in Gwinnett County, etc), it’s my belief(and hopefully you will agree) that every intersection can be optimized for the tasks at hand. But one must first understand what the task at hand is.

Frankly, it does not matter where the traffic comes from or where it goes.  The intersection does not care.  We need to examine and optimize each intersection for maximum throughput.

I’ve done a bit of data collection from the GA DOT website, collected green signal southbound times, observed for more than 18 years the traffic on 141 southbound and the length of the traffic queues(or jam if you like), and then put the data to work in a spreadsheet to determine just how much extra “sugar”(or vehicles) are we really trying to squeeze into the “bag”(or through the intersection.

Please remember this is just a model based on averages.  Each day more vehicles could arrive earlier of fewer later.  This would explain why some days you exit St. Ives or Medlock Bridge neighborhoods and it is better or worse than the day before.  What we do know is that the traffic light is the same.

If we have vehicles arriving, on average, at the traffic light at State Bridge and 141 at the rate of 78 vehicles per light cycle, and on green the light can process around 70 vehicles southbound, the backup queue will build.  And since it is just under a 1/2 mile from State Bridge to Grove Point Road, we would expect that intersection to get blocked and have some issues.  Some days it is worse, and some days(such as last Valentine’s Day) much better.

Another hour or so of the same amount of traffic arriving into the queue and we can see the backup approach Wilson Road.

By my rough estimates, 8 or so more vehicles are getting added to the queue for each light cycle at State Bridge on average.  If we calculate what % that would be, it equals just over 11%.

(If we were trying to handle that 10 lbs of sugar, our backup would be 4.6 4 miles in one hour!)

Using the same data as above, but improving the throughput of 141 Southbound by adding a third lane south(making the right turn only lane a combo lane, we can estimate the impact.

By adding the third lane, which handles an additional 20 Southbound vehicles each light cycle, then we might never generate a backup at the intersection.

There could be times where the influx of vehicles far exceeds what we see on average.  But the third lane would then allow us to reduce that queue each and every light cycle.

It appears that we are not truly trying to pack ten pounds of sugar in a five pound bag.  It’s more like an additional 9 ounces.  And if we stretch that bag just a little (by adding that third through lane) we just might be able to make this work with a minimal amount of effort.

We will hear that we are just pushing the problem down the road.  Our drivers know that the section between State Bridge and Old Alabama Road, however is NOT at maximum capacity.  And it will only be handling up to an additional 22 vehicles every 2 minutes and 26 seconds across three lanes.  As it is now configured, I believe it will handle it well.

I believe that the “Ten Pounds of Sugar” statement has kept us from tackling our traffic problems here in Johns Creek.  The high cost of the traffic delays as I have calculated should have been more than enough incentive to look more carefully at the problems.

Improvements can be made.   What are we waiting for? Because if it is a Ten Pound Bag, then we are waiting for the wrong solution.