ADT criteria for one-lane, two-way temp. traffic signal 2

[ylin8888]

I am working on some construction alternatives for a bridge replacement project. I am exploring the option of alternating one way traffic. Its a two lane rural road on a horizontal tangent. Posted speed is 45 mph. Daily ADT is 10,000.

Does anyone know what is the ADT criteria that would make it not feasible to install a temporary traffic signal. Thanks.

 

[Drumchaser]

ylin8888

Do not recall any criteria. 10K sounds a little high, but have seen it done. It helped for us to have alternate routes available, and media blitz. And our location was in close proximity to a town.

 

[teeman]

The amount of traffic you can process is dependent on the length of your clearance intervals which is dependent on the length of the workzone.

The best treatment I have seen is a report issued by the Minnesota Department of Transportation in 1981 entitled "Traffic Control for One-Lane Bridges". Chapter 3 of NCHRP Report 358 "Recommended Practices for Use of Traffic Barrier and Control Treatments for Restricted Workzones" also provides guidelines for selection of signal control on two-way, one-lane workzones.

Under the best of conditions a traffic signal can only process a total of 1500 conflicting vehicles in an hour. As the length of the clearance intervals increases, the amount of conflicting vehicles you can process goes down. An ADT of 10,000 sound high for a two-lane one-way operation.

We have found that signals do not provide effective control during periods of overstaturation. Impatient or aggressive drivers often run the yellow and long red clearance intervals creating problems for the startup of the opposing phase. That leads to motorists on the opposing phase running their clearance and all red resulting in very poor operation and sometimes lockup. Flagger or police control really become necessary during periods when demand exceeds capacity.

 

[Drumchaser]

NCHRP Report 358 sounds like a great reference.

Having looked back, our signal was on a State Highway with an ADT of 4700. As also stated our site was in close proximity to a populated area that had other roadways available for passive detouring.
At peak times our signals performed better than expected. We have utilized temp. signal control on two-way, one-lane workzones at several locations in the past, all were off system bridges with very low ADT.

On the SH project we did not experience very poor operation or lockup, but all situations are unique.

The only way I would consider this w/10,000 ADT is under very special circumstances: Full support and understanding of the public, "effective" alternate route signing, media blitz, local law inforcement presence during peak hours, accelerated const. seq./phasing w/bonus penalty, and not to be installed during Holiday season.

Each situation is unique.

 

[ylin8888]

Thank you all for answering the thread.

To get a "quantitative measure" of the performance, I tried using Synchro to model the scenario. Turns out Synchro has this model under their example. The basic idea is to set up two signals at each end of the work zone and group them so the intersections will operate under one controller. A simple two-phase signal that allows one direction at a time was set up. Then, by adding a long all-red clearance interval between the phases to clear the space between the two signals.

For my case, the work zone is only about 200 feet long. Since I do not have the peak hour volume, I simply estimate a conservative 20% of the ADT as my peak hour volume and I assume a 50% split for the directional traffic. I also assume vehicles to travel at 15 mph through the work zone and use that to determine my all-red clearance interval.
With all the information inputted, I allowed the program to optimize the cycle length. The program suggests a cycle length of 270 seconds. The analysis shows that with 2000 peak hour traffic (20% of 10,000 ADT), the signal will be operating at LOS F (205 second delay) with a max V/C of 1.32, and a 95th queue of 2,800 feet. It does not appear the signal will perform well under this scenario.

I then tried different volumes to see if I can make it perform at LOS D and under capacity. (Over here in Connecticut, LOS D and a max V/C of less than 1 is generally considered the limit of acceptable performance.) With few rounds of trial and error, I was able to optimize the system at 1,200 peak hour traffic.The program suggests a cycle length of 130 seconds. The signal will be operating at LOS D (54.5 second delay) with a max V/C of 0.92, and a 95th queue of 750 feet.

The results indicate an ADT of 6,000 is probably what you can expect a temporary two-way control signal to work efficiently.

I do not think 6,000 is the answer to my question. I did the excecise simply to satisfy my own curiousity. I agreed with what Drumchaser said, each situation is unique.

 

[teeman]

The only refinement I could add to your analysis is that in Rhode Island the percent of ADT present in the peak commuter hours on an urban arterial is generally between 7 and 9% each hour.

 

[ACtrafficengr]

That's a very spread out peak, Teeman. Around here, peak hour is more like 15% in rural areas, 11% in urban areas.

"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928

"I'm searching for the questions, so my answers will make sense." - Stephen Brust

 

[teeman]

Rhode Island can almost be divided in half North to South into urban and rural areas. Two-lane arterials in the rural area generally don't approach a 10,000 ADT and many have ADTs significantly lower. In the urban portion it would be hard to find a two-lane arterial with an ADT less than 10,000.