SOURCES OF DATA FOR WORK ZONE PERFORMANCE MEASUREMENT

Once work zone performance measures have been selected, agencies need to define the data sources and methodologies that will be used to collect and compute those measures. For some measures, only one data source and/or methodology will exist for an agency; for others, several sources and methodologies may be available. Agencies must balance the data needs for performance measures with available resources and other factors to determine the most appropriate data source or methodology to use.

For each category of measures, agencies must consider the following:

• Data needs,
• Available data sources and data collection methodologies, and
• Computations required to transform the data into the measures desired.

EXPOSURE PERFORMANCE MEASURES

Work zone exposure performance measure data needs fall into three basic categories:

• Project characteristics,
• Work activity information, and
• Traffic volumes.

Table 6 summarizes both the data needs that may exist and the possible sources of data for each of these three categories. Typically, the extraction and documentation of most project characteristics for work zone performance measurement purposes must be done manually, since automated methods for extracting the key data elements do not currently exist within most agencies.

Depending on the agency, work activity and temporary lane closure data may be available electronically or require manual extraction and documentation. Work activities that involved staggered implementation of temporary lane closures at night (i.e., closing a single lane initially, then a second lane a short time later, a third lane still later, etc.) require additional effort to document accurately. If worker injury rates based on work activities are of interest, it will be necessary to obtain counts of workers present during each activity period. These data can be very time-consuming to obtain.

Historical or planning-level traffic volumes are normally limited to AADT estimates. If a finer level of detail is needed, the agency must use time-of-day distributions from nearby count station data to estimate hourly traffic volumes during the work zone. If mobility impacts are significant, such estimates may overstate the amount of traffic volumes passing through the work zone because of driver diversion to alternative routes and changes to departure times, destinations, or travel modes.

Table 6. Work Zone Exposure Performance Measure Data Needs and Sources

Data Needs	Sources of Data
Project Characteristics
Length Basic project phasing Major roadway capacity constraint locations, e.g., Long-term lane and shoulder closures Lane shifts Detours Narrowed lanes Sections with portable concrete barrier located close to travel lanes Construction vehicle access points	Project plans (especially traffic control plans) Agency construction management database
Work Activities
Dates and times of work activities Data about each short-duration, short-term or intermediate-term lane closure: Dates Installation and removal times Location Number of lanes closed and left open Length Number of workers present during work activity hours	Daily project inspector diaries Traffic control subcontractor daily activity logs Lane closure request/management databases Agency construction management databases 1 Contractor payroll records
Traffic Volumes
Annual Average Daily Traffic (AADT) counted or estimated for the facility Traffic count samples during time periods of interest Continuous hourly traffic volumes by direction Vehicle classifications (especially the percent of large trucks in the traffic stream)	Historical automatic traffic recorder (ATR) counts from nearby count stations Agency planning and project development AADT estimates Periodic volume sampling before and during the project via manual counts or temporary traffic counters Real-time volumes from existing TMC traffic sensors Real-time volumes from portable work zone ITS traffic sensors

ITS = intelligent transportation system
TMC = transportation management center

SAFETY PERFORMANCE MEASURES

Safety performance measure data needs depend on the particular measures that an agency has selected. In turn, the data source(s) available to an agency will influence which performance measures are of greatest value to the agency. Categories of data needs include:

• Traffic crashes,
• Worker accidents and injuries,
• Agency work zone inspection scores, and
• Service patrol or emergency medical service dispatches to the project.

Table 7 provides a summary of specific data needs and sources for each of these categories. For most agencies, traffic crash data serves as the primary source of work zone safety performance measure data. Crash data timeliness can be a significant issue for some agencies. Whereas significant time lags can be tolerated for post-project and bi-annual reviews of agency policies and procedures, use of crash data for safety performance measurement on current projects is significantly hindered. Some agencies have moved towards electronic crash record entry by investigating officers, which has significantly reduced lag times in obtaining crash data from a project location. Another option available is to establish relationships with the local law enforcement agency for key projects, and periodically (e.g., every two weeks) request copies of the actual crash reports prepared by officers within the project limits. This approach requires a time commitment by the highway agency to obtain the crash reports and manually enter the desired crash information into a database for analysis.

Agencies will have access to worker accident and injury data maintained by its own occupational safety division. However, since the majority of roadwork is performed by private-sector contractors, additional data sources will likely be needed in order to fully assess highway worker safety performance. The BLS database can provide general data on construction industry injuries and fatalities in a given state. Meanwhile, some agencies participate in the National Institute of Occupational Safety and Health (NIOSH) Fatality Assessment and Control Evaluation (FACE) program (12) . Highway worker fatality reports occurring in participating states can be reviewed for insights into the causes and contributing factors to the accident. If more comprehensive data are desired, an agency may also choose to establish a formal reporting process for injuries, similar to the program that the New York State DOT has established (3) . Some agencies may be able to obtain highway contractor injury records, but concerns about worker privacy must first be addressed.

Table 7. Work Zone Safety Performance Measure Data Needs and Sources

Data Needs	Sources of Data
Traffic Crashes
Time, location, and direction of travel Severity Manner of collision Contributing factors	Statewide crash database Manually-collected crash reports from the local police agency
Worker Accidents and Injuries
Time, location, and activity Type (i.e., injuries involving traffic) Severity	Agency occupational safety division records Agency-established injury reporting system U.S. Department of Labor Bureau of Labor Statistics (BLS) National Institute of Occupational Safety and Health (NIOSH) Fatality Assessment and Control Evaluations (FACE) Highway contractor injury records
Agency Work Zone Inspection Scores
Rating scores	Agency work zone inspections or field reviews
Service Patrol/Emergency Medical Service (EMS) Dispatch to Project Location
Time and location of dispatches Type of response (for service patrol dispatches)	Agency service patrol dispatch logs EMS dispatch logs

Agency work zone inspection scores can be a simple but effective data source for work zone safety performance measurement. Evaluation of the quality of many different features of each work zone (sign condition and placement, pavement marking quality, channelizing devices, barriers, etc.) can be used as a surrogate of agency efforts to ensure safe work zones. The use of multi-dimensional criteria to rate each of these features (i.e., a 1 to 5 scale) can provide much more useful information to agencies than simple pass/fail ratings of each work zone (9) . Such scores can be summed or averaged in different ways and tracked over time to see if agency efforts to improve work zones are being successful.

Another method to circumvent time lags in obtaining crash data from project locations is to use service patrol or emergency medical service dispatch logs. For service patrol dispatch data, information about each dispatch is needed in order to remove actions unrelated to the safety of the work zone. Examples of these include vehicle stalls or other motorist assistance activities, and the removal of non-construction debris in the roadway.

MOBILITY (TRAFFIC OPERATIONS) PERFORMANCE MEASURES

Data needs for work zone mobility performance measures also depend on the measures of interest to the agency. Likewise, data sources available to the agency can influence which measures the agency uses. For most agencies, available data sources will vary from project to project, and the choice of data source(s) will be fairly obvious.

Categories of data needs include:

• Traffic queues,
• Travel times and delays,
• Agency ratings of traffic mobility impacts, and
• Customer complaints/customer ratings.

Table 8 provides a summary of the data needs and available sources of data for work zone mobility performance measurement.

Manual documentation of traffic queues allows mobility performance measurement to occur at work zones where no other sources of mobility data are available. Project field staff could be called upon to provide this data, or other potential data sources could be used as listed in the table. If this data source is selected, it is important that upper agency management supports and emphasizes the importance of gathering the data to ensure that it is consistently done.

Table 8. Work Zone Mobility (Traffic Operations) Performance Measure Data Needs and Sources

Data Needs	Sources of Data
Traffic Queues
Beginning and ending time Location Direction of travel Location relative to work space and/or lane closure merging taper	Manual on-site observations by field personnel Visual observation via closed-circuit television operated by TMC staff Periodic drive-through inspections by staff dedicated to work zone traffic operations monitoring Existing TMC spot speed traffic sensors Portable work zone ITS spot speed traffic sensors (or other portable traffic monitoring devices) deployed for the project
Travel Times/Delays
Time Location of delays Direction of travel Historical travel times	Existing TMC spot speed traffic sensors Portable work zone ITS spot speed traffic sensors (or other portable traffic monitoring devices) deployed for the project Point-to-point travel time measurement systems (automatic vehicle location, automatic vehicle identification, license-plate recognition and tracking, Bluetooth tracking, cellular telephone signal tracking) 3rd party speed and travel time data Periodic drive-through inspections by staff dedicated to work zone traffic operations monitoring
Agency Ratings of Work Zone Mobility Impacts
Rating scores	Agency work zone inspections or field reviews of mobility impacts
Customer Complaints/Ratings
Complaints Survey results	Agency complaint files Survey response database

ITS = intelligent transportation system
TMC = transportation management center

This data source is best suited to locations that normally have no congestion and queuing present during the times when work zone impacts are of interest (e.g., during temporary lane closures). In this way, the queues that are documented at the project site can be attributed solely to the presence of the work zone. If queues and traffic congestion are normally present when work zone queue measurements are desired, some amount of "before" data will be required to factor out the pre-work zone impacts from what is observed during the work zone itself.

A simple form that can be used for documenting queue lengths by field personnel is provided in the appendix of this primer. It is recommended that multiple queue length estimates be recorded, and that the duration of the queue also be documented (a queue may exist for only a portion of a work period). The more detail gathered during each work zone activity that creates a traffic queue, the more accurate the agency can calculate estimates of the mobility impacts of the work zone.

Table 8 also indicates that a number of possible sources exist for obtaining travel time and delay data. Both existing transportation management center (TMC) systems and portable work zone intelligent transportation system (ITS) deployments can provide useful data from spot speed traffic sensors that are positioned along the roadway. Speeds can be extrapolated between sensors and linked together to estimate overall travel times along the roadway segment. The quality of these estimates depends on the spacing between sensors and whether the sensors are properly maintained and calibrated.

The use of portable work zone ITS continues to gain acceptance with state DOTs and other highway agencies nationally. Although few agencies will likely deploy such systems strictly for performance measurement purposes, they can be a useful source of mobility performance data. Several systems are available commercially, and many have been tested and validated in field trials (see the FHWA website at http://ops.fhwa.dot.gov/wz/its/index.htm for more information regarding these tests). The ability of agencies to deploy portable systems is further being enhanced through the development of portable traffic monitoring devices (PMTDs).

If use of a permanent TMC system is anticipated for measuring mobility performance at a particular work zone, it is important to verify beforehand that work zone activities will not temporarily disable the sensors. A disruption in data can occur because of any of the following:

• Temporary loss of power to the sensors,
• Inadvertent movement or removal of a sensor by the work crew,
• Parking of construction vehicles on or near a sensor, and/or
• Damage to the sensor (primarily a problem for inductive loop sensors imbedded in the pavement).

Regardless of whether a permanent TMC system or a portable work zone ITS deployment is going to be relied upon for work zone mobility performance data, several "tips" are provided below to maximize the probability that quality data will be available.

Point-to-point travel time data can also be used to obtain speed and travel time data in advance of, and through, a work zone. Available technologies for collecting point-to-point travel times include:

• Automatic vehicle location (AVL),
• Automatic vehicle identification (AVI),
• License-plate recognition,
• Bluetooth tracking, and
• Cellular telephone signal tracking.

AVL systems track (continuously or intermittently) an instrumented vehicles as it traverses a route. Fleet vehicles (buses, delivery companies, emergency vehicles, etc.) are common users of this type of technology. These systems can provide instantaneous speeds at specific locations as well as elapsed travel times over a given roadway segment. The quality of the data available depends on the frequency of vehicle position and speed updates. Typically, very few vehicles in a traffic stream will be outfitted with this type of technology, which may limit its usefulness for work zone mobility performance measurement. It is likely that most agencies will not have direct access to this type of data unless they use such a system for their own vehicles.

AVI systems rely on antennae mounted at specific locations that can detect a uniquely-numbered sensor in a vehicle at each antennae location and compute elapsed travel times between antennae locations. Electronic toll tags are the most common type of AVI system in use for this purpose. Consequently, work zones on or near toll facilities may have ready access to this data for traffic monitoring and performance measurement purposes.

Electronic license-plate recognition systems with plate number matching software function very similarly to AVI systems, and have also been shown to effectively track travel times through a work zone (14) . More recently, research on the ability to monitor and track electronic devices enabled with "Bluetooth" technology in vehicles traversing a segment of roadway has also shown promise for monitoring work zone travel times between two readers installed on the roadside (15) . Tests indicate that its effectiveness is dependent upon the level of market penetration of Bluetooth-enabled devices in the vehicles and traffic volume levels on the roadway segment. Operating in a slightly different format, technology also exists to track the global-positioning-signal (GPS) of navigation devices, and to track cellular telephone signals (via triangulation methods from multiple cellular telephone transmission towers in the area) as they traverse through a network (16) .

In some locations nationally, travel time data is being made available to agencies for purchase from private-sector providers. These providers "fuse" data from a range of systems and technologies like those described above to create a product that has market value. Several agencies are considering the purchase of this type of data on roadways where they currently do not have traffic surveillance. When work zones occur on these roadways, the third-party data can be used to assess work zone performance. Research continues to evaluate the quality of data that such providers can deliver.

Although point-to-point travel time data does have some advantages for agencies, there are also important caveats to consider if this type of data is to be used for work zone mobility performance measurement. First and foremost, it is important to recognize that this type of technology does not provide traffic volume data. Thus, it will be necessary to supplement these data with traffic count data, or make assumptions regarding the amount of traffic passing through the work zone over time. For AVI, license-plate recognition, and bluetooth systems, the distance between readers is also an important consideration in measuring work zone impacts. Longer distances between antennae also limit how well such systems can detect the physical extent of congestion. Short distances of congestion caused by a work zone can be "masked" somewhat when vehicles travel a significant portion of distance between antennae at near free-flow speeds. ²

In contrast to the various technologies available to electronically measure point-to-point travel times through a work zone, many agencies obtain samples of travel times and delays through their work zones during routine project inspections or through student interns or other staff who are dedicated to travel time data collection efforts. To be most useful, such measurements should be made during time periods when the impacts are anticipated to be the most significant, such as during peak hours or during times when lanes are temporarily closed.

Agency ratings of traffic conditions, customer complaints, and customer survey ratings have all been discussed previously in terms of their value for work zone safety performance measurement. Depending on agency resources, these data sources can be useful in mobility performance measurement as well. Consideration needs to be given to potential biases that may exist in these data (agency staff may rate traffic conditions higher than drivers might, for example). Even so, these data can be extremely useful to agencies for both project-level evaluations and program-level assessments of agency policies and procedures pertaining to work zone mobility.

So, which data source is the best for work zone mobility performance measurement? The answer to that question depends on the agency and the projects to be measured. All sources have their advantages and disadvantages. Table 9 provides an overall comparison to aid in the decision-making process.

Table 9. Comparison of Various Work Zone Mobility Data Sources

Data Source	Advantages	Disadvantages	Other Considerations
Manual Measurement of Queues:
By Field personnel	Easy to implement Minimal additional cost	Increases work load of field personnel Not as useful at locations with pre-work zone congestion	Important to note location of start and end of queue relative to work zone lane closure each work period
By visual observation on CCTV by TMC staff	Easy to implement Minimal additional cost	TMC staff can be called away to manage incidents or other transportation issues in the region	Staff may need to document queue extent by visible landmarks for later determination of lengths
Electronic Spot Speed Data:
From existing TMC already in place	Minimal additional cost "Before" data is available to do before-during comparisons	Location of devices may not be optimum for work zone assessment purposes	Important to ensure that sensors will remain operational during work activities
From work zone ITS devices	Can control where devices are placed Minimal additional cost if system installed to provide real-time travel time information or other purposes	Work zone ITS is sometimes costly to include in a project	Important to make sure that sensors will extend beyond the limits of anticipated congestion
From portable traffic monitoring devices	Relatively inexpensive Easy to deploy and retrieve Can be easily moved as needed	Devices may have to be recharged regularly	Important to make sure that sensors will extend beyond the limits of anticipated congestion
From truck transponder data	Does not require agency to purchase technology to deploy Does not require technology to be moved or maintained	Sample size can be an issue for truck transponder data May require purchasing from third-party vendors	Important to remember that the spot speeds will be distributed across the segment length for which they are requested
Electronic Point-to-Point Travel Time Data:
From AVL systems	Very accurate tracking of speed profiles possible Potential exists for determining beginning and ending points of queues	Vehicle fleets to draw data from are limited	Will require agreements with agencies or vendors who collect these data
From AVI toll tags	Available sample size can be fairly high Easily implemented on toll facilities	Deployment of additional transponder readers will increase costs	Most useful in regions where a significant portion of the driving population has toll tags May require agreement with toll agency to gather data
From license plate recognition systems	Available sample size can be fairly high	Costly to implement	May create concerns about privacy with local citizens
From bluetooth readers	Data can be obtained unobtrusively from roadside devices	Detection range can vary depending on site conditions	Dependent on the volume of traffic present and market penetration of bluetooth devices
From cell phone tracking	Large potential sample size within traffic stream	Requires agreements with third-party vendors to obtain data	Dependent on the volume of traffic present
Other:
Customer surveys	Perceptions about performance can be obtained Can evaluate across a broad range of user groups	Can be costly to perform, especially to obtain demographically-balanced data	Surveys generally have a low (< 30 percent) response rate, which increases the sample size needed for useful results
Citizen complaints	Problems are identified very fast	Only negative input is received	Typically requires documentation of how complaint was resolved
Ratings or scoring by agency staff	Agency can adjust data elements and amount of data collected as needed Can be incorporated into existing inspections at many agencies	Agency assessments of its own activities may not match public perceptions	Correlations between ratings and other measures (i.e., safety) have not been well established

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