QuickZone: Modeling In the Zone
With the revised Federal Work Zone Safety and Mobility Rule now in effect, this modeling tool can help DOTs comply.
With road repair projects on the rise across the Nation, reducing congestion caused by work zones and improving mobility is more important than ever. About one-quarter of nonrecurring motorist delay is attributable to work zones, which also are cited as second only to poor traffic flow as a source of traveler dissatisfaction, according to research by the Federal Highway Administration (FHWA).
The FHWA study, Moving Ahead: The American Public Speaks on Roadways and Transportation in Communities (FHWA-OP-01-017), reveals that highway users tend to view roadway repairs and associated work zones as one of the major causes of traffic delays. The report states that one of the key steps to increase user satisfaction with highways is to reduce work zone delays. Accurately predicting such delays and planning effective construction phasing and detour routes can help reduce driver frustration.
Although no single analysis tool is ideal for all work zones, the software program QuickZone is one of many solutions in a highway agency's toolbox. Released by FHWA in 2002, QuickZone can help State departments of transportation (DOTs) and metropolitan planning organizations estimate the impact of work zone activities on traffic flow. Since 2002, State and local transportation agencies and construction contractors have used the inexpensive software program to estimate costs, traffic delays, and backups due to work zones and to compare the effects of mitigation strategies. An enhanced QuickZone 2.0 debuted in 2005. Now the program is poised to be even more beneficial as State and local agencies move to comply with the revised Work Zone Safety and Mobility Rule, which took effect in October 2007. (See "Revised Work Zone Rule")
Work Zones and Congestion
The growing congestion on U.S. highways is well documented. According to The 2007 Urban Mobility Report by the Texas Transportation Institute (TTI), "Congestion caused urban Americans to travel 4.2 billion hours more and to purchase an extra 2.9 billion gallons of fuel for a congestion cost of $78 billion" in 2005.
Unlike congestion caused by routine heavy traffic during daily peak travel periods, nonrecurring events generally result in unexpected travel delays. According to FHWA, work zones account for about 482 million vehicle hours of delay—24 percent of nonrecurring congestion and 12 percent of total congestion.
Work zones have adverse impacts on traveler and worker safety. In 2005 nearly 2.7 million people were injured and 43,443 people died on the Nation's roads. In 2006 there were 1,010 work zone fatalities, and each year, more than 40,000 people are injured in work zone-related crashes.
There are broader implications as well. Work zone impacts can extend beyond the physical location of the construction itself to affect safety and mobility miles away.
The trend toward longer and longer periods of peak congestion complicates the picture. TTI's The 2007 Urban Mobility Report indicates that annual delay for the peak-period traveler increased from 14 hours in 1982 to 38 hours in 2005 (48 hours in large cities). Ever higher traffic volumes on many highways make it difficult to perform work in or near travel lanes during much of the day because of the impacts posed to workers and the traveling public. As a result, the window to perform roadwork without severely affecting traffic is shrinking; today, about one-third of work zones are active primarily at night.
Revised Work Zone Rule
Anticipating and aggressively mitigating congestion caused by work zones can help relieve the problem. To help meet this goal, FHWA published the revised Work Zone Safety and Mobility Rule in September 2004. All State and local governments that receive Federal-aid funding were required to comply with the rule no later than October 12, 2007.
"The rule has been updated and revised to encourage agencies to address the mobility impacts as well as safety impacts created by working on the roadways," explains Ken Wood, a traffic operations engineer at FHWA's Resource Center in Olympia Fields, IL. "The changes to the regulation will encourage broader consideration of the safety and mobility impacts of work zones across project development, and the implementation of strategies that help manage these impacts during project delivery."
The rule has three primary components and goals. First, it calls for each State and local DOT to implement an overall policy on work zone safety and mobility to institutionalize the consideration and management of work zone impacts. Second, the rule requires establishment of agency-level processes to support policy implementation, including procedures for assessing the impacts of work zones, analyzing data, conducting training, and reviewing processes. Third, the rule calls for establishing project-level procedures to assess and manage the impacts of individual projects.
For a DOT, establishing an overall policy is the first step toward institutionalizing the planning, design, and operational strategies that reduce congestion and crashes due to work zones. Because of the high rates of retirement and turnover within DOTs and the increasing use of consultants, formalizing processes and practices will help ensure a consistent way of doing business across projects. Formalized processes also will lead to greater consistency and uniformity for highway users traveling through work zones.
Recognizing that not all road projects cause the same level of impact, the updated rule establishes a category for "significant" projects. A significant project is one that by itself or in combination with other nearby projects is anticipated to cause sustained impacts that are greater than considered tolerable according to State policy and/or engineering judgment. All projects on the interstate system within the boundaries of a designated Transportation Management Area are deemed significant if they occupy a location for more than 3 days with either intermittent or continuous lane closures.
The Need for QuickZone
Designation of significant projects triggers the need for further procedures for assessing work zone impacts, which is where analysis tools such as QuickZone come into play. QuickZone can help States and localities meet this need if they have not yet developed their own approaches or do not have the resources for the complexity, time, and expense involved in microsimulation analyses.
"As the compliance date drew near, transportation agencies considered several work zone analysis tools to assist in assessing the work zone mobility impacts," says Daniel Grate, a traffic operations engineer at FHWA's Resource Center in Atlanta, GA. "QuickZone is a tool of interest for many. It is considered one of the viable tools available to assist in assessing work zone impacts during all phases of the project development process, including planning, design, construction, maintenance, and operations."
FHWA's Turner-Fairbank Highway Research Center in McLean, VA, first developed QuickZone following the 1998 release of FHWA's study, Meeting the Customer's Needs for Mobility and Safety During Construction and Maintenance Operations. The report stated that the delay costs incurred by road users from work zones typically are not considered when construction zones are planned. The report's authors recommended developing an analytic tool, such as an easy-to-use software program, that would estimate and quantify work zone delays and resulting user costs.
Very few State and local highway officials or construction contractors could determine the true cost of a road construction or improvement project, according to the study, even after the project was completed. In the overwhelming majority of cases, officials and contractors calculated only "hard costs," such as labor and materials. But every road project also incurs "soft costs"—the extra minutes or even hours spent by motorists and their passengers in negotiating the delays caused by work zones. This type of traveler delay is significant, but its cost is rarely calculated.
Meanwhile, travelers must operate with only a vague idea of how long delays will last. Thus, a tool to quantify delays and estimate user costs would benefit everyone affected by work zones, including highway officials, workers, and motorists.
The QuickZone software is a Microsoft® Excel®-based application using Visual Basic® for Applications. Any computer with Excel 97 or a later release can use it. The only other requirement is a Windows®-based operating system with minimal memory and processing speed. QuickZone is an open-source application, which means that users may access the software's source code and customize it to suit their specific needs. QuickZone initially cost $195, including basic user support. QuickZone 2.0 runs approximately $250 but is free to those who purchased the original program.
Relieving Work Zone Congestion in the National Parks
QuickZone is proving useful not just in urban areas and highway corridors, but even in national parks. In Utah, the National Park Service used the software to plan a major rehabilitation of the main road through Zion National Park.
A primary concern was the potential problem for visitors entering the park through the town of Springdale during the construction work. Traffic queues often occurred at this visitors' entrance even under normal conditions.
Staff from FHWA's Central Federal Lands Highway Division (CFLHD) used QuickZone to estimate the number of vehicles that would queue up because of the road work during the peak tourist period of June-October. The analysis indicated that queues reaching into Springdale likely would occur unless changes were made to the proposed traffic control plan. Project engineers then reevaluated the construction phasing and came up with a better traffic plan.
CFLHD officials also used QuickZone to plan reconstruction of a 30-kilometer (18.6-mile) section of the Beartooth Highway, just outside Yellowstone National Park in Montana and Wyoming. This section had not been rebuilt since the original road construction in 1936. QuickZone helped evaluate a series of four planned work zones requiring flaggers, to provide an estimate of the cumulative delay that a motorist likely would encounter from the work zones and to improve coordination of lane closures.
Typical QuickZone users are State and local highway officials and others involved in planning highway construction. However, consultants also might use QuickZone to analyze project alternatives.
Sketch Planning Using QuickZone
QuickZone calculates the traffic delays and average and maximum queue lengths that could result from lane restrictions in both urban and suburban work zones. The software also facilitates tradeoff analyses between costs of construction and delays; evaluates how modifying the schedule, such as changing the time of day or season for various construction phases, might affect traffic delays; predicts queues and delays associated with mitigation strategies to reduce work zone impacts; and facilitates calculating incentives and disincentives for construction contractors to reduce user delay.
QuickZone is designed to calculate the difference between a roadway network's capacity and the actual number of vehicles using the network. The excess volume is expressed as a queue. The software uses standard queuing theory and volume-capacity ratios to generate its estimates.
A similar virtue is that the program is deterministic rather than stochastic. That is, QuickZone runs one direct calculation rather than a series of calculations using a random variable approach and then averaging those outputs. Thus, QuickZone produces the same results every time it is run, with no random variation to the outputs. Also, deterministic models are quicker to execute as they do not require the outputs of multiple runs to be averaged to derive the results. On the other hand, because drivers are not predictable, averaging using probabilistic models has virtues that a deterministic model does not.
Several mitigation strategies are built into QuickZone, including diversion to a detour route; techniques to manage demand, such as time shifting and trip cancellations; mode shifts to transit; and traveler information services using intelligent transportation systems. The program also facilitates evaluating construction alternatives such as full road closures.
Leading up to a QuickZone analysis, the user needs to gather four critical data components:
- Data on the roadway facility under construction and adjacent alternative routes in the travel corridor
- Data on the work zone strategy and phasing plan, including anticipated capacity reductions due to the work zone
- Data on travel demand, including travel patterns in the corridor prior to construction
- Data on planned strategies to mitigate congestion during each construction phase, including estimates of capacity changes
Using these data, QuickZone compares expected travel demand with the proposed capacity hour by hour through the life of a project to estimate delays and queues on the facility. By performing this hourly calculation for each phase of a project, the software takes into account anticipated travel demand throughout the day as well as seasonal variations (such as summer versus winter travel).
Unlike microsimulations, QuickZone requires orders of magnitude less input data, so the results are not nearly as detailed. While microsimulations can generate individual vehicle trajectories on a second-by-second basis, QuickZone gives overall network delay and length of queue. The software's level of detail is completely appropriate for less complex work zones, such as simple lane closures on high- or low-volume freeways and flagger operations on two-way, one-lane rural roadways. QuickZone is robust enough to handle many types of work zones, but for highly complex projects like interstate-to-interstate interchange projects, traffic managers should opt for a more detailed model.
Advantages of QuickZone
A benefit of QuickZone is that States and localities usually can input data they already have in hand, such as average annual daily traffic. Minor additions might be necessary, but nothing like the quantity of data needed for other more cost-prohibitive microsimulation models.
Inputting data for a typical work zone network should take less than 1 hour, depending on the complexity of the project or network. Once the data are entered, QuickZone can produce results—in graphic, tabular, or spreadsheet format—in less than 1 minute. The program will display the amount of delay in vehicle-hours as well as the maximum length of the anticipated queue.
Highway officials, planners, and contractors then can analyze the numbers to determine whether the delay is reasonable and acceptable—or "tolerable," in the words of the new work zone rule. If so, they can proceed as planned. If not, QuickZone offers suggestions for reducing the delay, such as informing the news media and the public about the planned work zone so drivers can find alternate routes, activating variable message signs to inform motorists of the scheduled dates and times of the work, or retiming traffic signals on detour routes so motorists will not have to stop at multiple red lights.
FHWA researchers performed validation testing in Florida, Ohio, Tennessee, Virginia, and Wisconsin and found that QuickZone estimates are accurate within plus or minus 10 percent.
Highway agency personnel can use the program to perform analyses at every stage of construction from planning and design to construction and operation. Traffic engineers can evaluate various work zone alignments to determine the impacts associated with full closure of one or multiple lanes for varying lengths of time. During construction, QuickZone can help highway officials and contractors decide whether day or nighttime work will cause the least overall delay.
Because QuickZone is customizable through an agreement between the user and the vendor on technical support issues, programmers can easily use it for other purposes. For example, with the necessary data elements, a highway agency could predict delays in locations prone to a high number of crashes or plan alternative emergency evacuation routes.
New Features Introduced In QuickZone 2.0
QuickZone 2.0 reflects lessons learned from applications of the earlier software and incorporates the following new features:
- Improved two-way, one-lane operations modeling, including flagger operations
- Improved ability to model more complex projects, including projects with multiple work zones and different work occurring in each work zone at various times
- Enhanced detour modeling, including tracking of increased travel time on long detour routes
The program's updated output statistics enable users to target problem work zones.
Version 2.0 also includes a wider variety of performance measures that users can track, graph, and analyze, including length of total mainline queue, total mainline delay in vehicle hours, total costs per passenger car delay, total travel time in minutes, and detour delay costs. Users can compare the results to preconstruction conditions to assess progress.
Successful State Applications
Numerous States are successfully using the new QuickZone. For example, the Mississippi Department of Transportation is funding a Mississippi State University study of traffic flow in rural highway work zones, with special emphasis on speed. "QuickZone 2.0 has been [customized for Mississippi] to estimate rural work zone delays, which may not be that significant compared to work zone delays in major metropolitan areas," says Li Zhang, assistant professor of civil and environmental engineering at the university. "The improved models are calibrated using data collected from Mississippi."
The Maryland State Highway Administration's (SHA) experience with the initial QuickZone software captures the benefits of the program. SHA used QuickZone to analyze evening road closures for its ongoing replacement of the Woodrow Wilson Bridge outside Washington, DC. During one phase of the project, nighttime road closures were planned from midnight until 4 a.m. When the road work began, it became clear that 4 hours were not enough when coupled with the required setup and takedown times.
Project engineers used QuickZone to analyze multiple scenarios for extending the duration of the lane closure and the number of lanes closed. The analysis showed there would be little difference in the impact on drivers if the closures began at 9 p.m. and the opening time was extended to 5 a.m. The contractor made these changes to the schedule, reducing this phase of the project from an estimated 6 months to 2 months.
Based on past success, Maryland plans to use QuickZone 2.0 on sever-al developing transportation projects, according to Jawad Paracha, assistant chief in the Traffic Development & Support Division of SHA's Office of Traffic & Safety. "The Federal Work Zone Safety and Mobility Rule requires us to analyze work zone traffic control alternatives and consider systemwide impacts in developing Transportation Management Plans," he says. "Depending on the complexity of a project, Maryland plans to use a tiered approach: starting with Maryland's Lane Closure Analysis Program for simple cases, QuickZone 2.0 for simple cases with network impacts, and then simulation tools such as CORSIM, VISSIM, and SimTraffic for relatively complex scenarios requiring detailed analysis."
In sum, QuickZone 2.0 continues to provide a more realistic and complete view of total construction costs, but now is especially timely and effective in helping DOTs comply with the work zone rule that recently came into force.
States assisted FHWA in the initial validation process for QuickZone and have continued to help FHWA refine it. In fact, many of the upgrades that FHWA did for version 2.0 were a direct result of information and feedback received from partner States. FHWA first established a partnership with the Maryland State Highway Administration, then further modified QuickZone as a result of collaboration with other State and local transportation agencies. Through the QuickZone Partnership Program, FHWA produced and shared new versions of software with partners who then shared feedback, and some even developed customized versions. The partnership, no longer formally active, originally included seven member States: Maryland, North Carolina, Ohio, Pennsylvania, Utah, Washington, and Wisconsin.
Several States have developed innovative ways to use the software. Maryland customized QuickZone with its own capacity estimation model to derive traffic delay estimates for different types of work zones, among other information. (Due to geographic differences in how drivers respond to work zone delays, however, FHWA decided not to add Maryland's feature to QuickZone 2.0.)
Several States wanted to enhance QuickZone so they could import data directly from traffic counters. In Ohio, software developers were interested in altering the program to accept traffic counts and arrival times automatically from data collection sites throughout the State. The anticipated benefits were time saved by faster data entry and greater accuracy compared to manual data entry.
The Wisconsin Department of Transportation attached a geographic information system application to its version of QuickZone. Users now are able to click on a map to find an intersection or other exact location and input the necessary network data. This feature helps plan detour routes and determine travel speeds and distances between locations.
Deborah Curtis is a highway research engineer on the Travel Management Team of FHWA's Office of Operations Research and Development.
For more information, contact Deborah Curtis at 202-493-3267 or firstname.lastname@example.org. QuickZone 2.0 is available for purchase from the McTransTM Center, 800-226-1013, 352-392-0378, mctrans.ce.ufl.edu; or PC-TRANS, 785-864-2599, www.kutc.ku.edu/cgiwrap/kutc/pctrans/index.php. Past purchasers of the original QuickZone should use the same contact information to obtain their free upgrade to QuickZone 2.0.