A comment from “Just Some Guy:”
Steve – While I agree that everything you’ve said sounds correct statistically, in my opinion, we need to dig deeper in the analysis and additionally we need a chart showing the traffic load for each hour of the day (what’s the load at 7AM, 11AM, 5PM, etc) for this discussion.
Because while it’s true that if you divide the daily load of 38-40,000 vehicles by 24 hours, you do indeed get an hourly average of around 1650 vehicles.
So statistically you’re correct.
But of course in reality that hourly rate varies quite bit throughout the day.There are not 1600 vehicles at 2AM any more than there’s only 1600 during rush hour.
And while you guessed that there were 6800 at rush, it was only that, a guess.
So we need that chart.
I’M guessing that a chart will show that saturation occurs quickly at rush hours.
It would be interesting to see.
And BTW, you mentioned “That would be 6,800 vehicles per hour for four lanes”, but there’s only 2 lanes in each direction, important at rush hour when (at least on Algonquin Rd.), one direction is loaded much more heavily at rush hour than the other direction (IMHO).
So that’s really only 3400 in one direction.
If we apply your analysis method to the intersection of Algonquin and Roselle Rd, for example, then someone needs to be indicted for squandering all that money on such an elaborate intersection (right turn lanes, double left turn lanes, 3 lanes in each direction).
But I believe it was probably designed for PEAK traffic load (I admit I’m guessing here myself), not average hourly load.
Outside of rush hour, while it’s a busy intersection to be sure, all that roadway isn’t needed.
Of course, they had a lot of space for that intersection; the Algonquin/Randall intersection, not so much.
So it was easier to build.
So while I totally disagree with Pro that your were lying, I think we need to dig deeper in the data to see what’s really going on.
All I know is that Algonquin/Randall intersection is VERY jammed up most of the time during the day without the rush hour.
Rush hour? It’s bad enough on a good day.
Is it worth that much (let’s be honest, it’s really more like $100-150 mil)?
Well, since as you noted, traffic rates aren’t increasing, I’d say yes, because if it’s done right (HA! Whatever THAT means – different discussion), it should be good for a long time to come.
So do it and get it over with!!
BTW I’m also guessing that bridges aren’t designed using the “average load” method, but rather the peak load, plus some!
A reply from Steve Willson:
Dear Just Some Guy:
I agree with you, we absolutely should have hourly traffic counts.
In fact, it is derelict to proceed without this data.
Yet that’s exactly what the County is doing: making hugely expensive decisions without the data the Traffic Division should have given them.
In point of fact, I’ve tried for almost three years to get hourly traffic counts from the County without success.
So I’ve been forced to use estimates.
Fortunately there’s good data on the ratio of rush hour traffic to total traffic, which is how I came up with my initial estimate of 6,800 vehicles per hour during the peak period.
And, finally, early this year we finally got hourly left turn counts from the County.
Evidence from other traffic studies shows the ratio of left turns to through traffic is relatively constant.
That means we can now obtain a better estimate of through traffic during rush hour.
The ratio of daily left turns to total traffic is 7.9 to 1.
If you multiply the maximum number of left turns per hour south (415) by 7.9, you get about 3,300.
If you multiply the maximum number of left turns per hour north (388) by 7.9, you get about 3,000.
Add those together and you get about 6,400 cars per hour north and south total during rush hour. Subtract the left turns from the total to get through traffic.
That’s about 5,600 cars per hour at the peak.
So, in conclusion, the County has failed to provide hourly counts despite repeated requests and we now have two different methods of estimating peak traffic and both are lower than the capacity of the road.
Now, I want to ask you a question.
Do you think I’ve made a case strong enough that it is incumbent upon the County to provide strong evidence to contradict my conclusion, both about need and cost?
Or do you think the County should proceed to spend $97 million on the project without providing hourly traffic data and without explaining why the cost is a multiple of the average cost of building such roads in the urban areas of Illinois?