States estimate work zone traffic delay using QuickZone

Institute of Transportation Engineers. ITE Journal, Jun 2003 by Curtis, Deborah, Funderburg, Keri A

TO ESTIMATE WORK ZONE DELAYS AND MAXIMUM QUEUE LENGTHS IN THE UNITED STATES, THE FEDERAL HIGHWAY ADMINISTRATION DEVELOPED QUICKZONE, A SOFTWARE TOOL DESIGNED FOR USE BY TRANSPORTATION AGENCIES AND CONSTRUCTION CONTRACTORS AT EVERY STAGE OF HIGHWAY PROJECT DEVELOPMENT.

HIGHWAY USERS TEND TO VIEW roadway repairs and associated work zones as one of the major causes of traffic delays, according to the Federal Highway Administration's (FHWA) 2001 report, Moving Ahead: The American Public Speaks on Roadways and Transportation in Communities.1 The report states that one of the key steps to increase user satisfaction with a highway system is to reduce work zone delays. Accurately predicting such delays and planning effective work phasing and detour routes can help reduce driver frustration. To assist with these types of improvements, FHWA developed QuickZone, an easy-to-use software tool for estimating work zone delays.

THE QUICKZONE PROGRAM

Researchers at FHWA's Turner-Fairbank Highway Research Center in McLean, VA, USA, developed QuickZone as part of the Strategic Workzone Analysis Tools (SWAT) program. The software is a Microsoft(R) Excel-based application using Visual Basic for Applications. QuickZone is an open-source application; users have access to the softwares source code and can customize it to suit their special needs.

QuickZone is used to analyze the traffic delays and average and maximum queue lengths that likely would result from work zone lane restrictions in both urban and non-urban corridors. In addition, QuickZone:

* estimates the delay impacts of alternative construction phasing plans;

* supports trade-off analyses between costs of construction and delays;

* evaluates how different schedules, such as changes in time of day and season for various phases of construction, affect traffic delays;

* predicts queues and delays when mitigation strategies, such as variable message signs, ramp metering and media campaigns, are used to lessen work zone impacts to road users; and

* supports accurate calculation of incentives and disincentives based on user delay.

QuickZone is designed to compute the difference between the capacity of a roadway network and the number of vehicles attempting to traverse that network. The excess volume then is expressed as a queue on the network. QuickZone uses standard queuing theory and volume capacity ratios in its estimates.

There are a number of mitigation strategies built into QuickZone to alleviate some of the queues and resulting delay. These include diversion to a detour route; demand management techniques, such as time shifting and trip cancellations; accounting for mode shifts to transit, if available; and intelligent transportation system traveler information services. QuickZone also allows for evaluation of construction alternatives, such as full road closures.

State and local traffic design, construction and operations staff as well as construction contractors can benefit from using QuickZone. Prior to conducting a QuickZone analysis, the user must provide four critical data components:

* Network data describing the mainline facility under construction as well as adjacent alternative routes in the travel corridor;

* Project data describing the work zone strategy and phasing plan, including capacity reductions resulting from the work zones;

* Travel demand data describing patterns of pre-construction use of the corridor; and

* Corridor management data describing various congestion mitigation strategies to be implemented in each construction phase, including estimates of capacity changes from these mitigation strategies.

QuickZone uses these data to compare expected travel demand against proposed capacity by facility on an hour-by-hour basis for the life of the project, thus estimating delay and growth in the mainline queue. This hour-by-hour calculation is conducted for each phase of the project, taking into account both expected time-of-day use (for example, morning peak versus mid-day demand) and seasonal variation in travel demand (for example, expected August versus February travel demand).

FHWA stresses that QuickZone is not a highly accurate simulation model but rather an easy-to-use traffic analysis tool. Validation testing performed in five states-Florida, Ohio, Tennessee, Virginia and Wisconsin-has shown that the estimates produced by QuickZone are accurate within or -10 percent.

QuickZone is sophisticated enough for application during every stage of a highway construction project, including policy development, planning, design and operations. For example, traffic engineers can employ the program during the early design stage to evaluate various alternatives for project construction and work zone alignment, including whether to use a full closure for a shorter duration versus multiple lane closures with a longer overall project timeline. During construction, contractors can use QuickZone to determine how to phase a job, including whether night or day work will cause less congestion overall and how seasonal traffic fluctuations will affect delays.