The Federal Highway Administration has created a wealth of resources for anyone considering the use of work zone ITS. One of the very best is the Work Zone ITS Implementation Guide published in January of last year (FHWA-HOP-14-008). This great guide helps those considering work zone ITS for the first time, seasoned veterans, and everyone in between.
One of my favorite features is the assessment chart found on page 25. I was reminded of this great tool during a workshop at ATSSA’s Traffic Expo this past February. The speaker, and I wish I could remember who it was, said he uses it every time he is unsure whether the use of a system is justified.
It considers 5 factors with a simple scoring system. Let’s go through it now.
Factor 1 – Duration of work zone
• >1 construction season (10 points)
• 4-10 months (6 points)
• <4 months; procurement and installation timeline is available prior to work starting (3 points)
It is much easier to deploy a system quickly than it once was so I am not sure this is truly a factor any more. But certainly longer projects are easier to justify than shorter ones.
Factor 2 – Impact to traffic, businesses, destinations, etc.
• Significant (10 points)
• Moderate (6 points)
• Minimal (3 points)
You really can’t argue with this one.
Factor 3 – Queuing and Delay
• > 2 miles for periods > 2 hours per day (8 to 10 points)
• 1-2 miles for periods of 1-2 hours per day (6 to 8 points)
• < 1 mile, or queue length estimates are not available but preconstruction, recurring congestion exists for periods , 1 hour per day (4 points)
The value ranges for this factor are going to vary with the agency using them. For some a one mile queue is no big deal, while for others it is a crisis. More importantly you need to score predictable but dynamic queuing higher as it is more likely to result in end of queue crashes. Other factors like sight distance issues (covered below) should also be considered.
Factor 4 – Temporal Aspects of Traffic Impacts
• Unreasonable for a time that covers more than just peak periods (10 points)
• Unreasonable during most of morning and afternoon peak periods in either direction (6 points)
• Unreasonable during most of a peak hour in either direction (3 points)
• Unpredictable, highly variable traffic volumes (1 point)
This could be the “phone call” predictor. Projects that will result in many very unhappy members of the public certainly justify the use of additional tools like work zone ITS. It shows that you care and are working to mitigate the impacts as best you can.
Factor 5 – Specific Issues Expected (0 to 3 points each based on judgment)
• Traffic Speed Variability
• Back of Queue and Other Sight Distance Issues
• High Speeds/ Chronic Speeding
• Work Zone Congestion
• Availability of Alternate Routes
• Merging Conflicts and Hazards at Work Zone Tapers
• Work Zone Hazards/ Complex Traffic Control Layout
• Frequently Changing Operating Conditions for Traffic
• Variable Work Activities (That May Benefit From Using Variable Speed Limits)
• Oversize Vehicles (Percent Heavy Vehicles > 10%)
• Construction Vehicle Entry/ Exit Speed Differential Relative to Traffic
• Data Collection for Work Zone Performance Measures
• Unusual or Unpredictable Weather Patterns
These are all important, and it is easy to imagine a situation where a combination of these alone justifies use of a system. Next to last is data collection for performance measures. This is the most cost-effective way of accomplishing that, and it is required. So I would suggest adding another 5 points or so automatically for data collection.
Once you have scored each factor, you add them up.
30 points or more means you will see significant benefit/ cost ratio from use of a system.
10 to 30 points means it may provide some benefits and should be considered to mitigate impacts.
Less than 10 points means it may not provide enough benefit to justify the cost.
This is simple, easy to use, and should help agencies justify the use of systems where applicable. You may download a copy of the chart by clicking WZITSscore. Please consider sending this to everyone who needs it.