A PRIMER ON WORK ZONE SAFETY AND MOBILITY 

PERFORMANCE MEASUREMENT

September 2011

Number of 

Complaints 

about Traffic 

Conditions

Hours of 

Queuing > 2 

Miles

Lane-MileHours of 

Closures

Percent 

Increase in 

Injury 

Crashes

VehicleHours of 

Delay

Project 

Safety 

Inspection 

Scores
Notice

The Federal Highway Administration provides high quality information to 

serve Government, industry, and the public in a manner that promotes 

public understanding. Standards and policies are used to ensure and 

maximize the quality, objectivity, utility, and integrity of its information. 

FHWA periodically reviews quality issues and adjusts its programs and 

processes to ensure continuous quality improvement.
Technical Report Documentation Page 

1. Report No.

FHWA-HOP-11-033

2. Government Accession No. 3. Recipient's Catalog No.

4. Title and Subtitle

A PRIMER ON WORK ZONE SAFETY AND MOBILITY 

PERFORMANCE MEASUREMENT

5. Report Date

September 2011

6. Performing Organization Code

7. Author(s)

Gerald L. Ullman and Timothy J. Lomax – TTI

Tracy Scriba – FHWA

8. Performing Organization Report No.

9. Performing Organization Name and Address

Texas Transportation Institute

The Texas A&M University System

College Station, Texas 77843-3135

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

DTFH61-06-D-00007

12. Sponsoring Agency Name and Address

U.S. Department of Transportation

Federal Highway Administration

Office of Operations

1200 New Jersey Avenue, SE

Washington, DC 20590

13. Type of Report and Period Covered

14. Sponsoring Agency Code

15. Supplementary Notes

Project Leader: Tracy Scriba, FHWA

Project carried out under contract to Battelle for the FHWA Office of Operations.

16. Abstract

This primer has been developed to assist agencies in establishing and monitoring a useful set of 

work zone safety and mobility performance measures. Work zone performance measures are 

metrics that help to quantify how work zones impact travelers, residents, businesses and workers.

Work zone performance measures help agencies improve their understanding of how their 

decisions during planning, design, and construction affect work zone safety and mobility, and thus 

can help improve how they make decisions for future work zones.

The primer describes possible work zone performance measures, and provides guidance to help 

agencies select and implement measures that make sense for their own work zone programs. The 

primer outlines the methods and technologies that are available to gather data to monitor the

various possible measures and procedures for calculating specific performance measures from 

different types of work zone traffic monitoring data. The primer also discusses the use of measures 

across multiple projects to assess an agency’s overall efforts and outcomes against its policies and 

goals. 

17. Key Words

WORK ZONE SAFETY AND MOBILITY, TRAFFIC 

IMPACTS, PERFORMANCE MEASURES

18. Distribution Statement

No restrictions.

19. Security Classif.(of this report)

Unclassified

20. Security Classif.(of this page)

Unclassified

21. No. of Pages

67

22. Price

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized

iii

TABLE OF CONTENTS

LIST OF TABLES............................................................................................................iv

EXECUTIVE SUMMARY................................................................................................. v

INTRODUCTION............................................................................................................. 1

What are Work Zone Safety and Mobility Performance Measures? ..................... 1

Why Should Work Zone Performance Measures Be Used?................................. 1

How Can Work Zone Performance Be Measured?............................................... 2

Objectives of this Primer....................................................................................... 4

WORK ZONE TRAFFIC SAFETYAND MOBILITY 

PERFORMANCE MEASURE NEEDS ............................................................................ 5

Project-Level Performance Needs........................................................................ 6

Agency Program-Level Performance Needs ........................................................ 7

SELECTING WORK ZONE PERFORMANCE MEASURES........................................... 9

Exposure Performance Measures ........................................................................ 9

Safety Performance Measures ........................................................................... 11

Mobility (Traffic Operations) Performance Measures ......................................... 15

SOURCES OF DATA FOR WORK ZONE PERFORMANCE MEASUREMENT........... 23

Exposure Performance Measures ...................................................................... 23

Safety Performance Measures ........................................................................... 25

Mobility (Traffic Operations) Performance Measures ......................................... 27

ESTIMATING PERFORMANCE MEASURES .............................................................. 37

Estimating Delay from Queue Length Data ........................................................ 37

Estimating Queues and Delays from Spot Sensor Data..................................... 41

Using a Traffic Simulation Model to Estimate 

Work Zone Performance Measures.................................................................... 45

WORK ZONE PERFORMANCE MEASUREMENT: MAKING IT HAPPEN 

IN YOUR AGENCY ....................................................................................................... 47

REFERENCES .........................................................................................................................51

APPENDIX: DATA COLLECTION FORM FOR MANUAL DOCUMENTATION OF 

QUEUE LENGTHS AND DURATION ........................................................................... 55
iv

LIST OF TABLES

Table 1. Potential Exposure Measures ........................................................................ 10

Table 2. Potential Safety Measures ............................................................................. 12

Table 3. Potential Queuing Measures ......................................................................... 16

Table 4. Potential Delay Measurest.............................................................................. 18

Table 5. Other Potential Mobility-Related Measures .................................................... 22

Table 6. Work Zone Exposure Performance Measure Data Needs and Sources ........ 24

Table 7. Work Zone Safety Performance Measure Data Needs and Sources ............. 26

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

and Sources ................................................................................................... 28

Table 9. Comparison of Various Work Zone Mobility Data Sources............................. 34

LIST OF FIGURES

Figure 1. Steps to Estimate Travel Time Delays from Queue Length Data................... 38

Figure 2. Components of Work Zone Delay. ................................................................ 39

Figure 3. Steps to Estimate Queue Length and Delays from 

Spot Speed Sensor Data............................................................................................... 41

Figure 4. Example of Sensor Speed Analysis to Determine Duration 

and Length of Queue..................................................................................................... 43
v

EXECUTIVE SUMMARY

Work zone performance measures are metrics that help to quantify how work zones 

impact travelers, residents, businesses and workers. Some measures describe the 

impacts of a specific work zone (project-level metrics), whereas other measures 

describe the impacts of a set of work zones (agency program-level metrics). What is 

expected to occur at a work zone with regard to safety or mobility impacts can be quite 

different from what is ultimately experienced at a site. Every work zone is unique, and 

the combined effects of design decisions, work phasing and sequencing operations, and 

impact mitigation strategies implemented at a site can be challenging to predict 

beforehand. Work zone performance measures help agencies improve their 

understanding of how their decisions during planning, design, and construction affect

work zone safety and mobility, and thus can help improve how they make decisions for 

future work zones.

Work zone performance measurement does not need to be an overwhelming activity for 

an agency. Not all work zones need to be measured, and those work zones that are 

measured do not necessarily need to be monitored at all times. Work zone 

performance measurement should be driven by agency and other stakeholder needs 

and priorities. One advantage of establishing work zone performance measures is that 

it focuses attention on what is considered important to the agency and stakeholders. 

To be useful, it is important for agency staff to understand:

• What is being measured,

• How it is being measured, and

• Why it is being measured. 

Efforts to improve work zone policies, processes, and procedures will be more effective 

if agencies also look at measures across multiple projects to assess their overall efforts 

and outcomes. Tracking how often an agency meets its performance expectations for

work zone safety and mobility across multiple work zones can be more indicative of 

overall performance and useful as program-level performance measures.

Agencies should choose a few good measures carefully based on their particular needs 

and characteristics, communicate those to all stakeholders and staff, and track them 

clearly, seriously, and consistently. Three basic types of performance measures are 

useful to quantify work zone safety and mobility impacts:

• Exposure measures,

• Safety measures, and

• Mobility (traffic operations) measures.
vi

Exposure measures describe the amount of time, roadway space, and/or vehicle travel 

that a work zone or a collection of work zones affects or requires. Safety measures 

describe how crash risk has changed for the individual motorist and/or for the traveling 

public in general, relative to pre-work zone levels. Safety measures can also be defined 

for contractor or agency personnel working on the roadway. Finally, mobility (traffic 

operations) measures describe how travel mobility has been affected for motorists (and 

potentially other types of travelers as well).

Work zone performance measures should: 

• Relate to the safety and mobility goals and objectives that the agency has 

established for itself,

• Be consistent with the measures used in impact assessment efforts for work zone 

planning and design analyses,

• Characterize the different facets of impacts that are occurring,

• Enable the agency to evaluate the effects of alternative strategies for mitigating 

traffic impacts caused by work zones, and

• Be compatible with other performance measures that an agency is using to evaluate 

its system.

Once work zone performance measures have been selected, agencies need to define 

the data sources, collection techniques, and calculation methodologies that will be used 

to 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 sources or 

methodologies to use. 
1

INTRODUCTION

Work zones can cause significant traffic congestion and safety impacts. Agencies strive 

to manage these impacts as best possible so as to meet the needs of its customers, 

complete the project effectively, and support regional mobility and economy. On 

September 9, 2004, the Federal Highway Administration (FHWA) amended its 

regulation (23 CFR Part 630 Subpart J) that governs traffic safety and mobility in 

highway and street work zones (1). One provision in the rule requires states to use both 

traffic safety and operational data to help improve agency processes and procedures to 

address work zone impacts. Specifically, states are encouraged to develop and 

implement systematic procedures that assess work zone impacts in project 

development, and to manage traffic safety and mobility impacts during project 

implementation. One way that agencies can improve these efforts is through the use of 

performance measures. 

WHAT ARE WORK ZONE TRAFFIC SAFETY AND MOBILITY 

PERFORMANCE MEASURES?

Work zone performance measures are metrics that help to quantify how work zones 

impact travelers, residents, businesses and workers. Some measures describe the 

impacts of a specific work zone (project-level metrics), whereas other measures

describe the impacts of a set of work zones (agency program-level metrics). Some 

examples of possible work zone performance measures include:

• The average peak-period delay to vehicles entering a work zone,

• The percent of time that a work zone queue exceeds an agency-established

allowable threshold,

• The average percent increase in crashes in freeway work zones in a given state, 

and

• The number of injury crashes occurring during temporary lane closures on 

particular types of roadways.

WHY SHOULD WORK ZONE PERFORMANCE MEASURES BE USED?

Safety or mobility impacts predicted for a work zone during planning and design can be 

quite different from what is ultimately experienced at a site. Every work zone is unique, 

and the combined effects of design decisions, work phasing and sequencing operations, 

and impact mitigation strategies implemented at a site can be challenging to predict 

beforehand. Work zone performance measures help agencies understand how their 

decisions affect work zone safety and mobility. This allows agencies to improve 
2

conditions at current work zones as well improve how they make decisions for future

work zones.

Work zone traffic safety and mobility performance measures have a variety of other 

uses to state departments of transportation (DOTs) and other highway agencies. 

Specifically, performance measures allow agencies to: 

• Assess whether they are meeting their own goals and objectives regarding 

acceptable work zone traffic impacts;

• Identify specific problems or issues that may be occurring at a particular work 

zone;

• Review and improve their work zone policies and procedures;

• Review and improve the accuracy of traffic impact assessment tools being used 

during work zone planning and design;

• Improve the prediction of expected benefits of impact mitigation strategies that 

may be included in the transportation management plan (TMP) of a project; and

• Better “tell their story” about work zone impacts, and effects of mitigation 

strategies implemented to reduce those impacts, to elected officials and to the 

public. 

Work zone performance measurement need not be an overwhelming activity for an 

agency. Rather, agencies should choose a few good measures carefully based on their 

particular needs and characteristics, communicate those to all stakeholders and staff, 

and track them clearly, seriously, and consistently.

HOW CAN WORK ZONE PERFORMANCE BE MEASURED?

Not all work zones need to be measured, and those work zones that are measured do 

not necessarily need to be monitored at all times. Work zone performance 

measurement should be driven by agency and other stakeholder needs and priorities. 

One advantage of establishing work zone performance measures is that it focuses 

attention on what is considered important to the agency and stakeholders. 

To be useful, it is important is for agency staff to understand:

• What is being measured,

• How it is being measured, and

• Why it is being measured. 

Ultimately, an agency may begin work zone performance measurement efforts on a 

limited basis by focusing on a few key performance measures for only a few projects 

each year. Then, as agency staff becomes more familiar with how and why work zone 
3

performance measures are used, the number and types of measures examined and the 

projects included in the analysis can be expanded.

Work zone safety and mobility performance measurement efforts can 

evolve over time as agency staff becomes more proficient in computing 

and interpreting the measures of interest. 

Three basic types of performance measures are useful to quantify work zone safety and 

mobility impacts:

• Exposure measures,

• Safety measures, and

• Mobility (traffic operations) measures.

Exposure measures describe the amount of time, work activity periods, roadway 

space, and/or vehicle travel that a work zone or a collection of work zones affects or 

requires. Exposure measures are also usually needed as a denominator for safety or 

mobility performance measures (such as the number of crashes per million-vehiclemiles of travel through a work zone). Both output and outcome exposure measures of 

performance can be useful. Output-based measures describe the amount of effort or 

other resources being expended (such as the number of hours of temporary lane 

closures a contractor has implemented at a project), whereas outcome-based measures

describe how many vehicles or vehicle-miles of travel occur through a work zone or 

group of work zones. 

As the name implies, safety measures describe how crash risk has changed for the 

individual motorist and/or for the traveling public in general, relative to pre-work zone 

levels. Safety measures can also be defined for contractor or agency personnel 

working on the roadway. Most safety measures are outcome based, such as the 

increase in injury crashes or the change in overall vehicle crash costs in a work zone. 

However, a few agencies do track output-based measures of certain efforts to reduce 

crashes as surrogates to safety impacts, with the assumption that such efforts result in 

improved safety. An example of such a measure would be the hours of additional law 

enforcement assigned to work zones in an agency’s jurisdiction.

Finally, mobility (traffic operations) measures describe how travel mobility has been 

affected for motorists (and potentially other types of travelers as well). Travel delays 

caused by work zones are an obvious example of this type of performance measure. 

However, other measures related to, or correlated with, delay are also available. For 

example, queue length and duration is a performance measure used by some agencies. 

Other agencies use average speed through the work zone as a measure. Most traffic 
4

operations measures are outcome-based. However, output measures of efforts to 

reduce delays and queues might also be important to an agency. 

Often, the safety and mobility data are combined with exposure data into other 

performance measures, such as the number of traffic crashes that occur per million 

vehicle miles of travel in a work zone. This process allows agencies to compare safety 

and mobility impacts across projects and over time, and also to aggregate those 

impacts across multiple projects. In other cases, additional computations and analyses 

may be required to obtain useful performance measures. An example of such analyses 

is when data is collected on the length and duration of queue lengths at a work zone, 

and the agency is interested in knowing how these queues translate into vehicle delays 

through the work zone.

OBJECTIVE OF THIS PRIMER

This primer has been developed to assist agencies in establishing and monitoring a 

useful set of work zone safety and mobility performance measures. The primer includes 

guidance on both project-level and agency program-level performance measure needs, 

defines a number of possible work zone performance measures that agencies can use, 

and describes the methods and technologies that are available to gather data to monitor 

them. The primer also outlines procedures on how to calculate specific performance 

measures from different types of work zone traffic monitoring data, and on use of the 

measures across multiple projects to assess compliance to agency policies and goals. 

Much of the information presented in this primer was based on pilot study research of 

work zone performance measures for projects in several states nationally. Multiple 

methods of collecting traffic operations data and computing performance measures from 

the data were used simultaneously at each project in the study. This simultaneous 

analysis allowed a comparison of the relative level of effort and precision of 

performance measures obtained from each data collection method. The reader is 

encouraged to review the final report of that pilot study effort for additional insights into 

work zone traffic safety and mobility performance measurement (2). In addition, this 

primer contains information from a recent scan of state DOT best practices for work 

zone impact assessment, data collection, and performance measurement (3). 
5

WORK ZONE PERFORMANCE MEASURE NEEDS

Conceptually, an agency can select from a wide range of potential measures for 

monitoring work zone safety and mobility performance. Examples of safety measures 

being used by some agencies include (3): 

• Crash statistics (frequencies, rates, and types; injuries and fatalities),

• Frequency of work zone intrusions,

• Speeds and speed variance,

• Percent of motorists exceeding the speed limit,

• Speeding citations issued,

• Service patrol or fire department dispatch frequency,

• Work zone inspection scores, and

• Worker fatalities and injuries.

Meanwhile, work zone mobility measures in use by certain agencies include:

• Delay,

• Queue length,

• Queue duration,

• Speeds,

• Volume-to-capacity ratio,

• Level of service,

• Volume (throughput),

• Percent of time operating at free-flow speed, and

• Percent of work zones meeting expectations for traffic flow.

For many of the safety and mobility measures listed, some exposure data and 

performance measure needs are also implied. Examples of exposure measures that 

have been used by agencies to normalize safety and/or mobility performance measures 

in work zones or to describe the amount of mitigation effort expended include:

• Vehicle-miles-travelled through the work zone, 

• Number of vehicles passing through the work zone,

• Number of hours of work activity, and

• Hours of dedicated enforcement in the work zone.

Finally, some measures can actually cut across multiple categories. For example, user 

costs can be computed from the delay and crash data as another type of performance 

measure (4). Likewise, customer surveys and complaints, although more commonly 
6

considered an indication of work zone mobility, may actually be influenced by both 

safety and mobility concerns. 

PROJECT- LEVEL PERFORMANCE MEASURE NEEDS

An agency should begin the process of selecting work zone performance measures by 

examining its current goals, objectives, and thresholds of acceptability for work zone 

performance. Performance measures are desired which can be easily compared to 

those goals, objectives, and thresholds to see how well the agency is meeting these 

criteria. Agencies should also consider the types of traffic impacts analyses it performs 

during work zone planning and design. In many agencies, one or two impact 

assessment tools are used for most analyses because agency staff is most familiar with 

those tools (3). One of the uses of work zone performance measures is to evaluate 

how well work zone impact assessments of planning and design decisions reflect what 

actually happens once the work zone is implemented in the field. 

Not all work zones are created equal. One project may require just a few work activity 

periods that create intense delays (with several other work periods of no impacts to 

motorists), whereas another project may have a comparatively small, but consistent 

delay to motorists throughout the duration of the project. Both projects may thus 

generate the same amount of total delay overall, but would likely be perceived quite 

differently by the public. Therefore, agencies will typically also need to select more than 

one performance measure in each category to fully capture all facets of the impacts that 

are occurring. 

With few exceptions, agencies have the option of choosing:

• When work should occur on a particular roadway,

• How much of the roadway to allocate to the work and how much to leave for 

traffic to use ,

• What construction strategies and techniques to use, and

• What techniques or strategies to use to mitigate the impacts of the work zone 

and improve roadway capacity, safety, traffic flow, etc. 

The performance measures selected should allow agencies to assess the effectiveness 

of these types of decisions as well. It may be desirable to establish separate 

performance measures for different project phases, work operations, time periods 

during the day or night, or other criteria in order to better assess the ramifications of the 

decisions that were made. Depending on the measures selected, it may be necessary 

to obtain data during a few key days or weeks in an overall project (e.g., the first week 

of each phase change), rather than have to collect a large amount of data over the 
7

entire duration of a project. By being targeted and selective, an agency can maximize 

the effectiveness of its efforts to monitor and evaluate work zone performance. 

Finally, some agencies have begun to monitor and track congestion and travel time 

reliability measures on an ongoing basis on certain roadways in its jurisdiction. 

Selected work zone performance measures should be compatible with other trafficrelated performance measures the agency is using to evaluate overall operations.

Performance measures should: 

 Relate to the safety and mobility goals and objectives that the 

agency has established for itself;

 Be consistent with the measures used in impact assessment efforts 

for work zone planning and design analyses;

 Enable the agency to fully characterize the different facets of 

impacts that are occurring;

 Enable the agency to evaluate the effects of alternative strategies 

for mitigating traffic impacts caused by work zones; and

 Be compatible with other performance measures that an agency is 

using to evaluate its system.

AGENCY PROGRAM- LEVEL PERFORMANCE MEASURE NEEDS

Performance measurement begins at the project level, since that is where the impacts

the agency is trying to manage occur. However, not meeting agency-established goals 

and objectives on a single project may not be indicative of an overall performance issue. 

Agency efforts to improve its policies, processes, and procedures (as required by the 

Work Zone Safety and Mobility Rule (1)) will be enhanced if impacts are ultimately

aggregated and interpreted across multiple projects.

One of the major challenges that agencies face is how to properly aggregate the 

performance measures computed for individual projects so that useful assessments 

across multiple projects can be made. For example, should an agency compute an 

average increase in crash rates across all work zones it has monitored, or compute 

separate averages for each type of roadway on which the work zones were located? 

Should the number of projects where queue length thresholds were exceeded be 

summed together, or should they be counted based on the type of work that was being 

performed (resurfacing, pavement rehabilitation, roadway widening)?
8

Many factors will influence the magnitude of work zone safety and mobility impacts that 

occur. Site characteristics, traffic volumes, and amount of truck traffic are just some 

examples. However, in terms of items under direct agency or contractor control, two 

main categories of decisions or actions exist:

• Type of work being performed (and how it is accomplished), and

• Traffic management approach used.

Agency program-level performance measures that are developed around these main 

categories will likely serve as a useful starting point for policy and procedure reviews. 

As was recommended for developing project-level measures, agencies may be best 

served by taking an incremental, iterative approach. For example, an agency might 

initially target work zones that involve either long-term or regular short-term lane 

closures on its freeway facilities, and focus efforts on developing and interpreting 

performance measures from that set of projects. As the agency develops an 

understanding of the measures and makes improvements to its processes pertaining to 

freeway work zones, the agency may begin to monitor and assess work zones on major 

urban arterial roadways. Eventually, work zones on two-lane highways could be added 

as well. For some measures, such as fatal crashes, an agency may track the measure 

across all of its work zones as one measure of overall work zone safety. For other 

measures, such as delay, an agency may sample a portion of its work zones as this 

may provide a sufficient indication of whether congestion estimates during planning and 

design and management efforts during construction are working.

Regardless of how an agency chooses to implement work zone performance measures 

into its regular program review process, the intent should be to collectively assess how 

well the work zones being tracked meet the policies and objectives the agency has 

established. This can often be most easily achieved by developing rates across 

multiple projects under the agency’s jurisdiction for how often the agency’s policy goals 

and objectives are being met. This does not necessarily involve the monitoring or 

collection and processing of large amounts of data on all projects. Agencies typically 

have a good idea of which projects will not induce significant impacts, and those which 

will. In addition, those projects may only experience them during certain phases or work 

tasks. By focusing their efforts on key times, agencies can keep work zone 

performance monitoring and evaluation to a manageable level.

Compliance rates across multiple work zones to agency-established work 

zone safety and mobility objectives are useful program-level performance 

measures. 
9

SELECTING USEFUL WORK ZONE 

PERFORMANCE MEASURES

In this section, several possible performance measures are described that can be useful 

for monitoring and characterizing safety and mobility impacts at highway work zones. 

The value of these measures is described, along with key considerations in obtaining 

and monitoring them. 

EXPOSURE PERFORMANCE MEASURES

Table 1 presents a list of possible performance measures pertaining to work zone 

exposure. Exposure measures describing vehicle throughput and miles of travel 

through work zones can be valuable for establishing safety and mobility rate-based 

measures as well as for tracking motorist diversion decisions. One of the challenges in

using vehicle-miles-travelled as an exposure measure is in defining what length or limits 

should be used in the computations. For major roadway rehabilitation and 

reconstruction projects, temporary geometric changes and traffic control features 

throughout the work zone may suggest that project limits be used for estimating vehicle 

miles traveled (VMT) of exposure. For other projects, though, vehicle exposure during 

the times when temporary lane closures are occurring (such as during hours of a hotmix asphalt overlay job) may be the exposure numbers of interest. In this case, the 

length of actual lane closures each day or night, rather than the total length of the 

project, is likely to be a more useful exposure measure. 

Exposure measures for tracking contractor activity and efficiency, as well as the amount 

of roadway space closed to traffic because of work zones, can also be useful for 

agencies. Examples of these types of measures include the percent of days (or nights) 

when work activity is occurring, the average number of work activity hours per day (or 

night), and the percent of work hours when one or more lanes are temporarily closed.

Actions taken, or technologies used, to improve safety or operations by an agency can 

also be measured as illustrated below (this list is not exhaustive):

• The number or percent of projects using portable concrete barrier to protect work 

spaces and/or pavement drop-offs,

• The number or percent of projects where the agency employed a reduced speed 

limit (possibly stratified by the amount of speed limit reduction), and

• The number or percent of projects where work zone intelligent transportation 

system technology was used.
10

Table 1. Potential Exposure Measures

Measure Why It is Important Considerations in Using It

Vehicles passing through the 

work zone, possibly stratified by 

work activity or lane closure

hours.

Required to compute other performance 

measures on a per vehicle basis.

Work zones with significant diversion require 

continuous counts in order to be accurate.

% change in vehicles passing 

through the work zone

Can represent traffic diverting from the work 

zone due to public information or other strategies

Requires continuous counts in order to be accurate.

Vehicle-miles-of travel through 

the work zone, possibly stratified 

by work activity/inactivity periods 

and /or lane closure times.

Standard measure of exposure for safety 

assessments

For some projects, total project length may be the 

appropriate length to use; for other projects, the length 

of each lane closure may be more appropriate for 

computing vehicle-miles-traveled of exposure.

% of days or nights when work 

activity occurs.

Describes intensity of effort being made to 

complete the job

Some projects are based on total calendar days, while 

other projects restrict when work can occur and should 

consider only the allowable work days/nights. 

Average hours of work per day 

or night.

Useful for assessing contractor utilization of time 

windows allowed for work

Overlap of subcontractor work efforts on complex jobs 

can make it difficult to define an overall start and end 

time each day or night.

% work activity hours with (1,2,3, 

etc.) lanes closed

Allows queue and delay measures to be 

stratified by amount of roadway capacity 

reduction involved

Lanes are sometimes closed in sequence over the 

course of a work shift (especially at night). It can be 

difficult to accurately capture these data in detail.

Average lane closure length Useful for evaluating compliance to maximum 

lane closure length specifications (if included in 

contract). Also, useful for extrapolating to similar 

projects that are not being monitored as closely. 

Lane closure lengths can change significantly during a 

shift as additional lanes are closed (especially at night).

Lane-mile-hours of closures May be useful in explaining high levels of delay 

or crash rate increases at certain projects

This measure is less intuitive than other measures.

Number or % of projects 

employing certain types of 

strategies or technologies to 

reduce safety or mobility impacts

It is a program-level measure of agency efforts to 

improve safety or mobility

Decisions to implement these are typically site specific. 

It may be necessary to stratify the measures by type of 

facility, type of work, or other site characteristics in 

order to be meaningful to the agency.
11

SAFETY PERFORMANCE MEASURES

Table 2 lists several work zone safetyrelated performance measures that 

agencies can use. Many states currently 

track overall work zone fatalities and 

injuries statewide on an annual basis. 

This approach provides a program-level 

indication of the safety impacts in work 

zones statewide, and is tracked over time 

to observe trends in crash frequency over 

time.

The percent of work zone crashes by 

manner of collision or other crash 

characteristics is a common type of

performance measure used by agencies 

to identify potential problem areas for 

countermeasure emphasis. These types 

of measures are dependent upon 

differences in traffic volumes and other 

factors from project to project (5). 

Consequently, examination of these types 

of measures at a program level (for all 

work zone crashes in the state, for 

example) can yield different conclusions 

from year to year as the characteristics of 

the projects changes each year. 

Table 2 also lists changes in work zone crash rates (or crash costs) as a potential safety 

performance measure. The use of crash rates reduces the effects of differences in 

exposure and other external factors between projects and allows for a more accurate 

assessment of work zone safety by the agency. The crash rate per million-vehiclemiles-traveled (MVMT) is a commonly-used measure, and can be stratified by crash 

severity (injury crashes per MVMT) or other crash characteristic. Other exposure 

measures can be used as well (e.g., crashes per hour of work activity). Program-level 

evaluation of agency safety policies and procedures will be best accomplished through 

crash rate measures.

The Ohio DOT compares the total 

number of work zone crashes that 

occur statewide each year to the 

annual amount of construction 

dollars that were let in that year 

(3).

A recent NCHRP study found that 

the crash risks to motorists at 

freeway work zones varied by time 

of day (daytime, nighttime) as well 

as by presence of work activity and 

or the temporary closure of travel 

lanes (5). The percent of crashes 

that involved rear-end collisions 

also varied by these factors as well 

as the annual average daily traffic 

(AADT) of the roadway where the 

work zone was located.
12

Table 2. Potential Safety Measures

Measure Why It is Important Considerations in Using It

Number of crashes per year or per 

project:

- Fatal

- Injury

- PDO

Actual crash counts represent the direct 

effects of work zones on safety.

Crash counts are dependent upon exposure (volumes, 

work zone length, and work hours at the project level; 

number of projects at the program level). Changes in 

funding from year to year could influence exposure and 

thus program level work zone crash counts.

% Crashes of certain types such as 

manner of collision (e.g., rear-end 

crashes), contributing factors (e.g., DWI 

crashes) 

Agency priorities for countermeasure 

implementation are often linked to the 

major contributors of work zone crashes.

Percentages of various crash types can also be affected 

by exposure. 

% Change in crash rate or absolute 

change from the expected no-work zone 

crash rate; possibly stratified by 

roadway, work zone type, severity

Changes in crash rates account for key 

differences in exposure that may also 

affect crash frequencies, thereby 

improving the comparability of the 

measure between sites.

This measure is computed for each individual project of 

interest; it requires information on exposure before and 

during each work zone

% of projects that exceed an acceptable 

crash rate in the work zone

A program-level measure to evaluate 

compliance with agency-established 

policies or targets

A reasonable number of projects must be evaluated for 

this to be meaningful to agencies. It can create 

substantial workload for the agency, especially if different 

roadway and project types are to be evaluated 

separately.

% Change in work zone crash costs from 

the expected no-work zone crash costs

Crash costs combine frequency and 

severity together in one measure. 

Results from multiple projects could be 

combined for program-level analysis by 

the agency.

This measure is also computed for each individual 

project of interest; it requires information on exposure 

before and during each work zone. 

Number of highway worker injuries or 

worker injury rate per hours worked

Workers are a particularly vulnerable 

population in work zones. 

Obtaining worker injury data from contractors can be 

difficult. The use of rates will require data on hours of 

worker exposure.
13

Measure Why It is Important Considerations in Using It

Work zone inspection scores Work zone inspections or reviews are 

under the control of the agency. This can 

simplify data collection and analysis.

Compliance to agency inspection standards is believed 

to be correlated to improved work zone safety, but 

research has not yet validated this. 

Number of work zone inspections 

performed

The number of inspections is a programlevel measure that agencies can use in 

conjunction with other safety measures to 

assess current policies and procedures.

Same as above.

Frequency or change in frequency of 

service patrol or fire department 

dispatches to a work zone

Crashes (especially severe crashes) will 

involve emergency responders. Agency 

access to this type of data can be faster 

than access to crash data.

Interagency agreements may be needed in order to 

obtain the data. For service patrols, non-crash event 

dispatches (stalls, motorist assistance with fuel, debris in 

road) may need to be excluded from the dataset to have 

a meaningful work zone measure. 
14

The use of crash costs allows an agency to incorporate the effects of both crash 

frequencies and crash severities into a single measure. It is possible, for example, for 

the number of property-damage-only (PDO) crashes to increase in a work zone (relative 

to a no-work zone condition) and the number of injury crashes to decrease slightly 

because of slower speeds through the work zone. The combined effect of those 

changes can be captured in the change in crash costs. Given that most states have a 

minimum damage cost reporting threshold for PDO crashes, increases in very minor 

crashes will not be captured in this measure, however.

Highway worker injuries or injury rates are another potentially useful work zone safety 

performance measure. Most agencies already track injuries of their own employees,

although not always distinguishing between injuries that are traffic related and those 

that are work related. Basic information on non-agency highway worker injuries can be 

obtained through the Bureau of Labor Statistics (BLS) database (6). 

Many agencies perform regular 

inspections or reviews of work zones 

under their jurisdiction. Standardizing 

the review forms and assessment criteria 

has allowed some state DOTs to 

establish safety performance measures 

using these data. Both project-level 

rating scores and program-level 

percentages of projects meeting agencyestablished score thresholds can be 

established (3). In the absence of a 

formal rating system, other agencies will 

typically track the number of project 

inspections or reviews done as a type of 

work zone safety performance measure.

Timely access to crash data is a problem that many agencies face when attempting to

measure work zone safety performance. At least one agency has attempted to 

circumvent this problem by examining service patrol and fire department dispatch 

frequency to locations within their work zones (3). Although information regarding crash 

location (and possibly crash severity) will be available through these sources, other 

crash characteristics will not. In addition, non-crash events (stalls, debris in road, etc.) 

may also be captured by service patrol dispatch logs, which can reduce the quality of 

this measure if these events cannot be separated from the dataset.

The New York State DOT assigns a 

rating score to each of a number of 

inspection criteria during each 

project review performed. All 

projects not meeting agency 

performance goals are targeted for 

immediate remedial action by project 

staff. The agency also evaluates the 

percentage of projects that meet its 

rating goals each year. For the past 

four years, approximately 85 percent 

of projects evaluated have met their

goals (3).
15

MOBILITY (TRAFFIC OPERATIONS) PERFORMANCE MEASURES

Queuing Performance Measures

Both queues and traffic delays reflect 

the effect of work zones on traveler 

mobility, and are correlated with each 

other. Both the safety considerations 

associated with the formation of 

queues and the fact that they can be 

directly measured more easily than 

delays has led several agencies to 

establish policies as to the maximum 

acceptable length and duration of 

work zone queues. Table 3 presents 

several work zone queue-related 

performance measures for agencies 

to consider.

As can be seen, the measures 

shown in Table 3 are more detailed 

than simply whether or not a queue 

formed at a given work zone. Queue 

frequency, length, and duration are 

all important attributes to be captured 

in work zone queue performance 

measures. Generally speaking, it is 

preferable to have multi-level 

performance measures rather than 

simple present/not present or yes/no 

performance measures whenever 

possible (9).

Frequency, length, and duration are needed to fully characterize traffic 

queues at work zones. All are important components in work zone 

queuing performance measures.

Both Ohio and Indiana (DOTs) have 

established policies on acceptable 

work zone queue length and duration 

as follows: 

• Queues less than 1 mile are 

acceptable at all times,

• Queues between 1 and 1.5 miles 

cannot exist for more than two 

consecutive hours, and

• Queues longer than 1.5 miles are 

not acceptable for any duration (7,

8). 

During a milling and overlay project on I95 in North Carolina, queues developed 

on only 26 percent of the days when 1 of 

2 travel lanes were closed in a given 

direction. Conversely, nighttime lane 

closures for construction work on I-405 in 

Seattle resulted in queues forming on 81 

percent of those nights when lanes were 

closed (2). When queues occurred at 

either site, the lengths and durations of 

the queues varied dramatically from day 

to day. 
16

Table 3. Potential Queuing Measures 

Measure Why It is Important Considerations in Using It

Number or % of days or 

work activity periods when 

queuing occurred

Some work zones have only occasional queues, 

whereas others will experience queues on almost 

daily basis

It is more difficult to detect and record infrequent 

queuing unless traffic conditions are being

continuously monitored and recorded.

Average queue duration Useful for road user cost computations Very short-duration queues cannot always be 

detected. Also, crashes or other external influences 

can skew work zone queue duration values. 

Average queue length Useful for road user cost computations Defining the beginning and ending points of a queue 

can be a challenge. Also, crashes or other external 

influences that occur can skew work zone queue 

lengths. 

Maximum queue length Maximum queue lengths can help agencies assess 

whether advance warning signage is placed far 

enough upstream of the lane closure to adequately 

warn approaching motorists.

Queue lengths can change rapidly over time, and 

may be at a maximum for only a very short period of 

time. Also, queue lengths may differ by lane,

depending on the geometrics of the roadway and 

driver behavior.

% Time when work zone 

queue length exceeds xx mi

Combines queue frequency, length, and duration 

into a single performance measure

Queues due strictly to external influences (weather, 

crashes) should be examined separately from 

queues that are due strictly to work zone operations 

and temporary lane closures. This measure will 

typically require continuous monitoring of traffic 

conditions.

Amount (or % of ADT) that 

encounters a queue

The number of vehicles that encounter a queue is 

useful for evaluating appropriate beginning and 

ending times of temporary lane closure periods. 

Queues can cause diversion from the work zone, 

the amount of which is difficult to predict. 

ADT = average daily traffic (vehicles per day)

xx = threshold level as defined by the agency
17

Agencies will likely be interested in examining queue performance measures that are 

due to certain work activities (temporary lane closures, close proximity of work 

equipment to travel lanes) separately from those measures that include external 

queuing influences in the work zone. For example, adverse weather conditions can 

slow vehicle speeds and increase gaps between vehicles, thereby increasing the 

likelihood of queues developing where one typically does not occur. The occurrence of 

a traffic crash in the limits of a work zone may also create a queue where one normally 

would not occur, or significantly increase the length or duration of a queue that normally 

exists. While it can be argued that those types of queues are also related in some 

fashion to the design of the work zone, queues that occur strictly because of work 

operations reflect directly upon agency work zone policies and procedures in terms of 

how many lanes are allowed to be closed or hours when lanes can be closed. 

Queuing performance measures in Table 3 are defined relative to a no-queue condition 

during the periods of work activity. The assumption is that any queues that develop are 

the direct result of the work activity and temporary lane closures required. If recurrent 

queues were occurring at the site before the project began, these queue performance 

measures would need to be defined in terms of changes from their pre-work zone 

levels. Likewise, if long-term lane closures were used at a project that resulted in 

queues only during peak periods, it may be more appropriate to evaluate queue 

performance measures strictly over the peak period at that site.

Delay Performance Measures

Table 4 describes several possible 

work zone delay performance 

measures for use. Delays are 

needed to estimate road user costs 

caused by work activities. Road user 

costs drive decisions regarding 

bidding approaches and contracting 

strategies employed, incentive and/or 

disincentive provisions used in the 

contract, techniques used to 

accelerate construction, and the 

traffic impact mitigation strategies that may be implemented. Separate delay measures 

are often used to describe the impacts of the work zone to an individual vehicle (delay 

per vehicle), and to the collective motoring public overall (total vehicle-hours of delay). 

The Oregon DOT work zone policy is to 

limit delays due to work zone lane 

closures to no more than 10 percent 

above the peak travel times that would 

normally have occurred traveling through 

a roadway corridor (10). The limit is for 

the entire corridor, regardless of the 

number of work zone lane closures in 

place in the corridor at one time. 
18

Table 4. Potential Delay Measures

Measure Why It is Important Considerations in Using It

Vehicle-hours of delay per:

- Work period

- Work period when 

queues are present

- Peak period

- Project 

Multiplied by the value of user travel time, these 

measures define road user costs that are 

attributable to work zone mobility impacts, stratified 

by the conditions and times when they occur.

In areas already experiencing recurrent 

congestion, it is necessary to first determine 

the delays normally occurring on the roadway 

prior to the start of the work zone

Average delay per:

- Entering vehicle

- Queued vehicle

- Peak period vehicle

Motorists are more sensitive to individual vehicle 

delays than to total delays; these measures can be 

stratified to better define the impacts to various 

vehicle subsets.

Continuous travel time and volume data are 

desired to compute average and maximum 

delay measures, as well as the percentage of 

vehicles which experience delays more than 

deemed acceptable by the agency.

Maximum per-vehicle delay Knowing the upper bound on maximum individual 

delay experienced during a project can be helpful 

in responding to public complaints about perceived 

level of mobility impacts.

External influences (crashes, vehicle stalls, 

weather conditions) can dramatically increase 

work zone delays. Delays during these events 

should be categorized separately from those 

due strictly to work activities.

% Vehicles experiencing 

delays greater than xx minutes

In addition to knowing the magnitude of delays, 

knowing what percentage of drivers are 

experiencing more than agency-defined tolerable 

delays is also important for program-level reviews.

Diversion from the work zone due to delays 

makes continuous travel time and volume 

monitoring highly desirable.

xx = threshold level as defined by the agency
19

Both total delay (vehicle-hours) and individual vehicle delays (minutes 

per vehicle) are important indicators of work zone mobility performance.

Recognizing that individual delays can vary significantly over the course of a project or 

even hours of a particular work shift, multiple versions of these delay measures may be 

needed to capture both the extreme and “typical” impacts. Another measure, percent of 

work activity time when motorist delays are exceeding some threshold, will be useful to 

agencies that have identified a maximum tolerable level of motorist work zone delay. 

In locations that are not experiencing recurrent congestion, any delays occurring are 

directly attributable to the work zone. In locations where recurrent congestion is already 

occurring, it will be necessary to establish baseline delays prior to the start of the work 

zone so that the additional impacts of the work zone can be appropriately determined.

Travel Time Reliability Performance Measures

In addition to the congestion and delays that can be created, work zones can also make 

travel times less predictable or reliable for motorists who regularly use a particular 

facility. Drivers want dependable travel times so that they can better plan their

departure and arrive at a destination near a desired time (11). 

Roadways with highly variable travel times require motorists to “buffer” in more time in 

their departure time decision to ensure that they are likely to arrive on time, even though 

there is a chance that they will arrive much earlier than necessary if travel conditions 

are favorable. One way to describe travel time reliability is through a buffer index

performance measure, defined for a particular time period (peak, nighttime, etc.) as: 

Buffer Index = 95thpercentile Travel Time−Average Travel Time

Average Travel Time (Equation 1) 

The use of the 95th percentile travel time as the upper limit implies that someone who 

allows that amount of time for their trip would arrive late no more than once every 20 

trips (or days). Similarly, use of an 80th percentile travel time in the above computation 

would correspond to arriving late no more than once every five trips (or days). 
20

Currently, most state DOTs do not 

establish separate work zone travel 

time reliability performance measures. 

However, efforts to evaluate the 

potential usefulness of work zone 

travel time reliability performance 

measures were positive (2). For those 

agencies that already track travel time 

reliability performance measures on a 

regular basis, examining work zone 

mobility-related impacts with this type 

of measure should be considered. 

Some agencies may use other 

measure to characterize travel time 

reliability on their facilities, such as a 

planning time index or the percent of 

time that congestion (i.e., delays or 

travel times) exceeds some defined 

threshold level. These same measures can continue to be monitored during work zone 

conditions as well, and the change attributable to the work zone can be calculated. 

Work zone travel time reliability performance measures should be 

considered in regions where travel time reliability is already being 

monitored.

The effect of long-term lane closures on 

travel time reliability due to two closelyspaced projects was recently evaluated 

for a section of I-15 in Las Vegas, 

Nevada (2). Results indicate that the 

closures increased the peak period 95th

percentile buffer index from 22 percent 

before the closures to 64 percent 

northbound during the closures. 

Southbound, the buffer index increased 

from 22 percent before the closures to 70 

percent during the closures. In other 

words, the presence of the work zone 

meant that drivers had to allow an 

additional 40 to 50 percent of their 

average travel times for their trips to 

ensure they did not arrive late at their 

destination.
21

Other Types of Work Zone Mobility Performance Measures

Although queues and travel time 

delays are the most direct indicators of 

work zone mobility impacts, some 

state DOTs have tried and are using 

other types of performance measures 

that relate to work zone mobility. 

Table 5 summarizes several of these 

types of measures. Average speeds 

in the work zone can provide an 

indication of the quality of service 

being provided. Often, multiple data 

collection locations are needed to fully 

characterize operating conditions 

throughout the work zone. Some agencies use level-of-service (LOS) as a mobilityrelated performance measure for work zones within or near at-grade intersections. 

Work zone volumes or throughput are another type of measure that has been used. A 

few agencies track the percent of time a project is operating at or near free-flow speeds 

as a work zone mobility performance measure. Although less objective than other

mobility-related performance measures, customer complaints or surveys are also used 

by many agencies to assess how well mobility is being maintained in work zones. 

The Missouri DOT uses a rating process 

during project inspections to determine 

the percent of work zones under its 

jurisdiction meeting agency expectations 

regarding traffic flow. Recently, the DOT 

has expanded the rating process to nontechnical employees who drive through a 

work zone during their daily travels. In 

addition, a website survey was created to 

allow motorists to rate a work zone as 

well (3).
22

Table 5. Other Potential Mobility-Related Measures

Measure Why It is Important Considerations in Using It

Average speed Speed is easy to measure, and can be obtained 

at multiple locations (if desired) to evaluate 

operating conditions in various parts of a work 

zone.

The location of data collection can have a 

significant effect on speeds obtained. If 

handheld devices are used, measurements 

must be taken from close to the actual travel 

lanes to reduce errors. 

Intersection Level-of-Service 

(LOS) maintained during the 

project

Some agencies use impact assessment tools 

that provide intersection LOS, and so have 

based their policies and acceptable thresholds 

around that measure.

LOS cannot be collected directly in the field. It

must be computed from volume, delay, and 

signal timing data. 

% Work zones meeting agency 

expectations for traffic flow

This is a program-level measure that can be 

directly and quickly obtained by agency staff as 

part of project field reviews and inspections.

Agency personnel performing the assessments 

may not all have the same expectations. Also, 

agency expectations may not always align with 

motorist expectations.

Customer complaints Complaints can help identify in real-time which 

work zones are creating major impacts, and 

allow agencies to implement corrective 

measures quickly. Most agencies already have 

procedures in place to track and respond to all 

complaints received from the public. 

Information received in a complaint can be 

subjective and incomplete. Agencies can 

spend considerable time deciphering and then 

responding to each complaint received.

Customer survey ratings Surveys about travel conditions in work zones 

can be done fairly quickly and can yield useful 

insights about problems and possible corrective 

actions.

Unless properly designed, survey results can 

be somewhat biased (positively or negatively), 

which can reduce their effectiveness.
23

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 
24

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 databases1

• 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

 1 Some agencies use construction management software (such as Trns•port SiteManager) to 

electronically record their daily diary entries on projects. Although currently not included as part of the 

capabilities of those systems, future enhancements could be made to these systems to allow users to 

easily extract, summarize, and report work zone exposure information (times of work activity, temporary 

lane closure statistics, etc.)
25

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) 

Ohio DOT personnel gather hard copies 

of police crash reports at major projects 

every two weeks and manually code that 

data into a database so that current 

crash statistics on those projects can be 

monitored. A team trained to identify 

underlying causes to crashes 

investigates major crash “hotspots” 

identified through the monitoring process 

so that the agency can make 

improvements to the work zone (3).
26

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.
27

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. 

The Pennsylvania DOT has 

attempted to use law enforcement 

personnel to collect queue length 

data while providing overtime-duty 

enforcement services at the work 

zone. The amount and quality of 

queue data collected by enforcement 

personnel to date has varied 

dramatically from project to project, 

making it difficult for the agency to 

rely on this data source (3).
28

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, 
29

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). 

One type of portable traffic monitoring 

device (PMTD) has been developed to fit 

within a standard temporary traffic control 

channelizing drum. The device consists

of a power supply, wireless 

communication capabilities, radar, and a 

global positioning system (GPS) antenna. 

The vendors of the device gather the data

(primarily speed), process it, and post it to 

an internet site for access by the highway 

agency personnel or whoever else has 

been authorized for access. The 

processed data can also be sent back out 

into the field to disseminate current travel 

times on portable changeable message 

signs or displayed on a public website. 

Tests of the technology through the 

national evaluation of the SafeTrip-21 

initiative were favorable (13).
30

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.

Tips for Using Spot Speed Traffic Sensor Data for Work Zone Mobility 

Performance Measures: 

 Ensure that sensors will exist within the work zone and upstream 

for a distance greater than the anticipated length of congestion and 

queues that may develop. 

 Deploy sensors as closely spaced as is practical and affordable, to 

increase travel time and delay measurement accuracy.

 Ensure that traffic sensor spot speed data will be archived for use 

in work zone performance measure computations.

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-topoint travel times include:

• Automatic vehicle location (AVL),

• Automatic vehicle identification (AVI),

• License-plate recognition,

During a recent test of permanent TMC 

system data usage for work zone mobility 

performance measurement, many of the 

inductive loop sensors that could have 

been used for work zone traffic data were 

found to be inoperable on nights of work 

activity. It was theorized that temporary 

power disruptions were required for the 

work activities, which rendered the spot 

speed sensors inoperable and made it 

impossible to measure traffic impacts on 

those nights (3).
31

• 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 uniquelynumbered 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 

The FHWA Office of Freight Management 

is examining the use of transponder data 

from large trucks for monitoring traffic 

conditions on various roadways. The 

usefulness of this dataset for work zone 

mobility performance measurement was 

inconclusive at most pilot test locations 

due to the low sample sizes available. At 

one urban freeway location where longterm lane closures were in place and 

peak-period travel conditions were 

significantly impacted, the transponder 

data were reasonably consistent with the

other available data sources at that site

(2).
32

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 

 2 Depending on the spacing between AVI antennae on the roadway segment of interest, it may be 

desirable to temporarily install portable AVI readers at strategic locations near the work zone (at the 

beginning of the lane closure, at the end of the work zone, at the location of the maximum length of queue 

expected, etc.) to precisely tailor the travel time data to the work zone region of interest.
33

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. 
34

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
35

Data Source Advantages Disadvantages Other Considerations

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 thirdparty 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

37

ESTIMATING WORK ZONE DELAY AND QUEUE LENGTH 

PERFORMANCE MEASURES

Although queues and delays both characterize the same congested conditions at a 

particular work zone, they do represent different measures of congestion. Each type of 

measure can either be obtained directly from the data, or estimated using extrapolation 

procedures or fundamental relationships of traffic flow. For example, elapsed point-topoint travel times can directly measure delays, whereas field personnel can directly

observe and record when and where the queue starts and ends. Conversely, spot 

speed sensors from a work zone ITS or from a functioning TMC can be extrapolated 

over segments of roadway to estimate travel times through a work zone. 

In some jurisdictions, both types of data may be used to measure work zone mobility 

performance. While the use of different measures is not necessarily a problem for 

project-level evaluation, it can create a challenge for agencies wanting to use a single 

type of measure (or both measures) for program-level assessments. If this is the case, 

agencies will need to estimate the other types of performance measures from the data 

they have collected. Fortunately, this is fairly easy to accomplish, and steps to do so 

are covered in this section of the primer. 

Two types of computations are described:

• Estimating travel time delays from manually-recorded queue length data, and

• Estimating travel time delays and queues from a series of spot sensors.

In addition, discussion is provided regarding the possible use of traffic simulation tools 

for estimating performance measures that are not monitored directly. 

ESTIMATING DELAY FROM QUEUE LENGTH DATA

When queues form at a work zone, traffic speeds are significantly lower through the 

queue than upstream or downstream of the queue. The difference between the normal 

speeds on the facility and the reduced speed through the queue creates the delay that a 

motorist joining the queue experiences. 

The process for estimating delay from manually-recorded queue length data is only 

appropriate for work zones in locations where recurrent congestion does not occur 

before a work zone is implemented so that assumptions can be made as to the speeds 

that would have existed prior to the installation of the work zone. Given these 

requirements, a simple three-step computation is all that is required to estimate delay 

from each queue length measurement recorded:
38

Figure 1. Steps to Estimate Travel Time Delays from Queue Length Data.

Estimate the Average Speed in Queue and in the 

Transition/Activity/Termination Areas

Queues result in travel time delays by creating slower speeds in both the queue and the 

transition/activity/termination areas of the work zone. If a queue has formed upstream 

of the lane closure bottleneck, it is first assumed that the flow rate through the work 

zone is at or near capacity. Given this assumption, speeds over the length of queue 

(Lq) are at the average speed in queue (Uq), and speeds over the length of the 

transition/activity/termination areas of the work zone (Lwz) are at the speed of capacity 

flow as illustrated below:

Step 1: Estimate the Average Speed in Queue

and in the Transition, Activity, and 

Termination Areas

Step 2: Compute Individual Vehicle Delay

through the Queue and the

Transition, Activity, andTermination 

Areas

Step 3: Sum Individual Vehicle Delays

 over the Duration of Queuing

1
39

 

Figure 2. Components of Work Zone Delay.

Assuming a linear speed-density relationship, the speed at capacity flow through the 

transition/activity/termination areas can be computed simply as one-half of the free-flow 

speed (Uf) on the facility. Upstream of the work zone, the queue that develops will be 

flowing at a speed less than the capacity flow speed. Again using a linear speeddensity relationship, the equation shown above produces an estimate of the average 

speed in queue as a function of the normal roadway capacity and the capacity through 

the work zone (WZ Capacity) (17). The capacity of the work zone can be estimated 

using procedures in the Highway Capacity Manual (HCM) (18). The HCM also provides 

procedures to estimate the normal capacity of the roadway segment. Typically, the 

following approximations will suffice:

• For 65- and 70-mph roadways: 2200 vehicles per hour per lane * number of 

lanes on the facility

• For 60-mph roadways: 2000 vehicles per hour per lane * number of lanes on the 

facility.

Compute Individual Vehicle Delay through the Queue and through the 

transition/activity/termination Areas

Assuming that the speeds computed in step 1 are maintained through the entire length 

of queue and work zone documented on the forms, estimates of average delays per 

vehicle through the queue and work zone can be computed. Travel at some threshold 

speed (most likely the desired speed or the posted work zone speed limit [UWZSL]) is

used as the basis against which the longer travel times would be compared:

2
40

Delay

Vehicle = Lq � 1uq

− 1

UWZSL� + Lwz � 1

uf

2

- 1

UWZSL� (Equation 2)

If the activity area of the work zone is fairly long, congestion may not develop at the lane 

closure bottleneck as assumed above but at the location of the work zone activity due to 

driver rubbernecking or other factors. While speeds may slow significantly because of 

the increased distraction and lead to congested travel conditions within the work zone, 

speeds in that congestion will be operating closer to the speed at capacity flow than 

they will be to the estimated average speed in queue. Consequently, it is important to 

apply the correct speed estimate (speed at capacity flow, speed in queue) to the correct 

amount of the length of queue. 

Calculation of motorist delay from queue length data requires 

documentation of the amount of the queue located within the work zone

and the amount that exists upstream of the work zone lane closure.

Sum Individual Vehicle Delays over the Duration of Queuing

Once the average delay per vehicle is estimated for each time interval that a queue is 

noted on the documentation form, the total vehicle-hours of delay is computed simply by 

multiplying the hourly volume by the average of the computed delay values at the 

beginning and ending of each hour. If the begin and end times of the lane closure and 

queue do not occur exactly on the hour, extrapolation techniques should be used to 

estimate the delays during that portion of an hour. 

Typically, the manual documentation of queues at a work zone implies a lack of other 

traffic data collection devices available at the project, including hourly traffic volume 

data obtained while the work zone is in place. As a result, it may be necessary to rely 

on historical traffic volumes for these computations. If only AADT volumes are 

available, they will need to be distributed over the hours of the day to arrive at estimated 

hourly volumes. 

During a pilot test of work zone performance measures in Seattle, a lack of queue 

location documentation hampered efforts to accurately estimate motorist delays 

from queue length data. Estimated delays due to a 4-mile queue varied between

5.9 minutes if the queue were located entirely within the work zone lane closure, to 

21.9 minutes if the queue were located entirely upstream of the work zone lane 

closure. At the Philadelphia pilot test site, the estimated delay for a 2.9-mile queue 

varied between 2.9 minutes and 29.8 minutes, depending on whether the queue 

was assumed to exist within or upstream of the work zone lane closure (2). 

3
41

The use of historical volumes for these (or any other volume-based) computations

implies an assumption that 1) all traffic that normally used the facility before the work 

zone began continued to do so once the work zone was in place, or) any motorist who 

diverted experienced delays by using an alternative route that was equal to the delays 

being experienced by motorists remaining on the roadway and passing through the 

queue and the work zone.

ESTIMATING QUEUES AND DELAYS FROM SPOT SENSOR DATA

To estimate the queue length that exists at a work zone when spot speed traffic sensor 

data is used to monitor work zone mobility performance, it is necessary to evaluate 

traffic speeds over time and compare those speed patterns between adjacent sensors. 

In essence, the goal is to identify the discontinuity in traffic flow conditions between two

adjacent sensors. The assumption made is that the beginning of the queue exists 

somewhere between those two sensor locations.

The process to estimate queue lengths and durations as well as travel time delays from 

spot sensor data consists of five basic steps:

Figure 3. Steps to Estimate Queue Length and Delays from Spot Speed Sensor 

Data.

Step 1: Divide the Roadway into 

Regions of Assumed Uniform Speed

Step 2: Examine Speeds and Volumes

Hour-by-Hour at each Sensor Location

Step 3: Compare Hourly Speed/Volume Profiles

across Sensors to Identify Length of

Queue

Step 4: Sum Region Lengths where Speeds are

below Thresholds 

Step 5: Compute Total Vehicle-Hours of Delay
42

Divide the Roadway into Regions of Assumed Uniform Speed

In step 1, the roadway section where a work zone exists is divided into a series of 

segments of various lengths (L), with conditions in each segment assumed to be 

represented by its corresponding spot sensor data of volumes (V), average speeds (U),

and detector occupancies (O) as illustrated below. Within each segment length, the 

travel time (TT) is estimated as the segment length divided by the average speed.

Illustration of Traffic Surveillance Estimates using Spot Sensor Data

Examine Speeds and Volumes Hour-by-Hour at each Sensor Location

To approximate queue lengths from spot sensors, the speeds at each sensor are 

examined in sequence and over time to identify the regions and times at each region in 

which speeds drop below a selected threshold. Speeds at successive sensor locations 

are examined together, and the length Li for each segment below the speed threshold is 

added together for each time interval of interest. In the example on the next page, spot 

traffic sensors are located 0.2 mile, 0.8 mile, and 1.3 miles upstream of the temporary 

lane closure. Project diary information indicates that a lane closure began at 9:00 AM 

and ended at 3:30 PM. 

Li Li+1 Li+2 Lengths

Vij, Uij, Oij

TTij = Li / Uij

Vi+1j, Ui+1j, Oi+1j

TTi+1j = Li+1 / Ui+1j

Vi+2j, Ui+2j, Oi+2j

TTi+2j = Li+2 / Ui+2j Travel Times

Travel

Times

1

2
43

Figure 4. Example of Sensor Speed Analysis to Determine Duration and Length of 

Queue.
44

Compare Hourly Speeds across Sensors to Identify Extent of Queue 

Propagation

Starting with the downstream region, the average speeds over time at each region are 

examined in sequence moving upstream to estimate the upstream end of the queue 

each hour. For each hour (or other analysis period preferred by the agency), the 

objective is to identify how far upstream the queue has propagated. To accomplish this, 

the agency should select a speed threshold it will use to define the difference between 

normal traffic flow and traffic flow in a queue. This threshold can be defined as part of 

the agency’s work zone policy or procedures in absolute terms (e.g., speeds below 10 

miles per hour, or speeds less than one-half of the free-flow speed of traffic on a 

facility), or in terms of the amount of reduction in speed observed by traffic approaching 

the work zone. Once a threshold is selected, it is a fairly simple task to determine the 

two regions in sequence that have a normal, high average speed at the upstream region 

and a low, congested speed indicative of the presence of queuing. The midpoint 

between the spot sensors of those two regions is where it is assumed that the upstream 

end of the queue is positioned during that hour. Performing this analysis hour-by-hour 

will result in a queue length profile over time at the work zone

For the above example, a 40 mph speed threshold was selected as indicating queued 

traffic conditions. Consequently, the analysis of speeds at the upstream sensor 

locations indicates that a queue began to develop at approximately 11:30 AM at the first 

sensor, which grew upstream and reduced speeds at the second sensor at about 12:30 

PM. The queue did not extend back to the third sensor, since speeds never did drop 

below 40 mph at that location during the hours of work activity. The estimated queue 

length each hour would therefore be as follows:

Time Estimated Location of 

Upstream End of Queue

Estimated Queue Length

11:00 am None 0

12:00 pm Between Sensors #1 and #2 0.2 + (0.6/2) = 0.5 mile

1:00 pm Between Sensors #2 and #3 0.2 + 0.6 + (0.5/2) = 1.05 mile

2:00 pm Between Sensors #2 and #3 1.05 mile

3:00 pm Between Sensors #2 and #3 1.05 mile

4:00 pm None 0

3
45

Sum Travel Times across Sensors to Compute Individual Motorist Delay

As noted previously, the travel time at 

any point in time across a segment of 

roadway (TT) is simply the length of that 

region (L) divided by the speed at that 

point in time (U). Summing the 

individual travel times for each region 

together provides a total travel time 

over the length of roadway of interest at 

that point in time. 

To estimate the work zone delay to an individual motorist approaching the work zone 

during a given hour, the travel times estimated in a pre-work zone condition are 

subtracted from those estimated from the speeds measured during the work zone over 

the same summed length of interest. As an alternative, a desired speed through the 

work zone can be defined and travel times based on that desired speed used to 

compare against actual work zone travel times. Such an approach might be used if the 

agency has posted a reduced speed limit through the work zone, and does not want 

delays measured against the normal, non-work zone speed limit and operating speeds. 

Compute Total Vehicle-Hours of Delay

The final step in the process is to sum the individual motorist delays occurring each 

hour that queuing and congestion has developed. This is the average individual 

motorist delay each hour as computed in step 4, multiplied by the number of vehicles 

measured as traversing those regions during each hour, summed and converted to total 

vehicle-hours of delay.

USING A TRAFFIC SIMULATION MODEL TO ESTIMATE WORK ZONE 

PERFORMANCE MEASURES

Conceptually, it is also possible to use a traffic simulation model to estimate work zone 

performance measures not recorded directly through data collection efforts. Such an 

approach may be desirable, for example, if the agency had already developed a model 

for assessing potential impacts during work zone planning and design. An agency 

could gain valuable insights into the effectiveness of their design modeling efforts by 

revisiting the assumptions and data used and seeing how the resulting analysis 

compared to what occurred in the field. 

The accuracy of both delay 

computations and queue length 

estimates using traffic sensor data are 

very dependent upon the distance 

between successive sensors. 

Estimation errors increase directly as 

the length between sensor increases.

4

5
46

A simulation model can also be used to estimate work zone performance measures that 

are not directly monitored in the field. To accomplish this, the model would first be 

calibrated to the pre-work zone conditions at a location. Then, the work zone would be 

added to the model, and the outputs calibrated to the conditions that were measured at 

the site. For example, if queue length and duration were measured through manual 

data collection methods, the model inputs and parameters would be adjusted 

systematically to match the documented queue patterns at the site. These adjustments

may mean reducing or increasing the traffic volumes approaching the work zone or 

entering and exiting at various ramps upstream or within the work zone; adjusting the 

capacity values used for the normal roadway and for the work zone; or adjusting the 

geometric inputs to the model to modify the resulting capacity flows achieved through 

the simulated roadway section and the work zone. Once the queue patterns have been 

sufficiently replicated in the model, the output would provide the individual vehicle 

delays and total vehicle-hours of delay. 

If this approach is used, it is important to correctly interpret and understand what the 

output from the model actually represents. For example, it may be necessary to 

significantly reduce the historical traffic volumes approaching the work zone in order to 

achieve the queue lengths observed in the field. This would imply that a significant 

amount of traffic diversion had occurred to other routes or travel modes. The estimates 

of individual motorist delay through the work zone could be fairly realistic, as they 

represent the delays incurred by a specific vehicle traversing a realistic length of queue 

and the work zone. However, if the simulation model did not include the alternative 

routes, the portion of traffic demand removed from the work zone would cause the

vehicle-hours of delay to be underestimated by the amount of that removed traffic. 

Unless the agency is convinced that the diverted traffic experienced no additional travel 

time to their ultimate destinations, some means of accounting for diverted traffic delays 

would be necessary. Agencies would also need to assess how realistic the estimated 

diversion amounts are for the work zone of interest. If the calculated diverted traffic 

amounts are considered to be excessive for the roadway corridor, it would be necessary 

to further adjust some of the other parameters (work zone capacity, driver behavior 

parameters) to calibrate the model and extract the output results of interest.
47

WORK ZONE PERFORMANCE MEASUREMENT: MAKING IT HAPPEN

IN YOUR AGENCY

Performance measurement can significantly improve work zone safety and operations. 

However, measurement does not just “happen.” Effective work zone performance 

measurement occurs when an agency plans for it and incorporates it into its overall 

organizational processes. As stated earlier, such processes should be based on an 

agency’s understanding of:

• What is being measured,

• How it is being measured, and

• Why it is being measured. 

Several good sources of information exist that are relevant to how to set up a work zone 

performance measurement program (9, 19, 20, 21). The following is a compilation of 

key steps that will facilitate agency efforts to implement work zone performance 

measurement. 

Identify and Engage Stakeholders and Other Work Zone Performance Measure 

Users

Agencies should begin their efforts to implement work zone performance measurement 

by determining those who can use and benefit from having good measures. This may 

include representatives from several divisions and offices within the agency as well as 

stakeholders outside of the agency. This group should be brought together to discuss 

and define the following:

• Needs for work zone performance measures,

• Work zone performance goals or targets (based on policy and procedures), and

• “Champions” for performance measurement.

This group helps to establish the “why” for work zone performance measurement. The 

group may also help to define how the measures will be used once they are available, 

such as to update requirements for monitoring in transportation management plans 

(TMPs) or in project plans, specifications, and estimates (PS&Es). 

Pick Work Zone Performance Measures

This step answers the “what” for work zone performance measurement. The 

information provided in this primer identifies several types of measures that can be 

used. Typically, it is more useful to select a limited number of key measures to track, 

rather than to try to follow a large number of measures that are related to each other. A 
48

target should be associated with each measure so that everyone knows what equates 

to success.

Identify Data Sources

This step is critical to the success of work zone performance measurement 

implementation. An agency may identify a very good performance measure, but not be 

able to obtain the data needed to compute and track it. It may be necessary to iterate 

between this step and the previous one to determine what measures will meet the 

needs of the agency and have the data necessary to compute them. Information 

provided in this primer can help an agency in determining what data it has available or 

can easily obtain to support work zone performance measurement. Whenever 

available, agencies should make use of existing data sources, such as real-time traffic 

sensor data from regional transportation management centers and already-established 

third-party agreements for travel time data, for its work zone performance measurement

efforts.

Define Analysis Requirements

In this step, an agency determines specifically how the data obtained will be translated 

to the desired work zone performance measures. Answers to questions such as the 

number of projects to monitor, the process to be used for selecting projects, the 

monitoring frequency of those projects, and the sample sizes of data to be obtained are 

resolved at this point. 

Assign Roles and Responsibilities

At this point, an agency should determine who will have responsibility for doing the data 

collection, analysis, and documentation of the performance measures. Typically, this 

step will have budgetary implications, since staff time and other resources will be 

needed. Determining where the funding will come from to support this effort is 

important at this stage, and is why it is important to determine who the champions for 

work zone performance measurement are within the agency and among the other 

stakeholders. 

Define Methods for Disseminating the Results 

This step is sometimes overlooked, but is very critical to the successful implementation 

of work zone performance measurement. Given that an agency has already determined 

the needs for performance measures, decisions are made at this step as to the best 

methods for getting those measures to those who need the information. In some cases, 

it may be desirable to make the measures available to the public or to other external 

users. In these instances, the use of “dashboard”-type displays of key measures on an 
49

agency’s website may be appropriate (22). In other cases, the agency may incorporate 

the results into its annual report. In still other cases, regular updates of the measures 

may be provided via email or through official memoranda to key users within and 

outside of the organization. 

Review and Refine Measures as Needed

This process should not be considered a “one-and-done” activity. Rather, it is an 

iterative process that continually improves work zone performance measurement. 

Changes in performance measurement needs, data sources, and improved knowledge 

and understanding of how to use the measures to improve agency operations will 

undoubtedly occur over time. An agency can take an incremental approach to work 

zone performance measurement, selecting a few key measures to target initially, and 

then revising or adding to those measures as understanding of them and of their value 

to the agency increases. Agencies should plan to revisit their work zone performance 

measurement program on a regular basis. One opportunity for regular review is during 

a work zone process review, which is required every two years by 23 CFR 630 Subpart 

J (1). 

51

REFERENCES

1. Work Zone Safety and Mobility. Code of Federal Regulations, Chapter 23, Part 

630—Preconstruction Procedures, Subpart J. U.S. Government Printing Office, 

Washington, DC, September 9, 2004.

2. Ullman, G.L., T.J. Lomax, F. Ye, and T. Scriba. Work Zone Performance Measures 

Pilot Test. Report No. FHWA-HOP-11-022. FHWA, U.S. Department of 

Transportation, Washington, DC. April 2011. Accessible at 

http://www.ops.fhwa.dot.gov/wz/resources/publications/fhwahop11022/fhwahop1102

2.pdf

3. Best Practices in Work Zone Assessment, Data Collection, and Performance 

Evaluation. Scan Team Report, NCHRP Project 20-68A, Scan 08-04. TRB,

National Research Council, Washington, DC. October 2010. Accessible at 

http://onlinepubs.trb.org/onlinepubs/nchrp/docs/NCHRP20-68A_08-04.pdf.

4. Hardy, M. and K. Wunderlich. Traffic Analysis Tools Volume IX: Work Zone 

Modeling and Simulation – A Guide for Analysts. Report No. FHWA-HOP-09-001. 

FHWA, U.S. Department of Transportation, Washington, DC. March 2009.

5. Ullman, G.L., M.D. Finley, J.E. Bryden, R. Srinivasan, and F.M. Council. Traffic 

Safety Evaluation of Nighttime and Daytime Work Zones. NCHRP Report No. 627. 

TRB, National Research Council, Washington, DC, July 2008.

6. Injuries, Illnesses, and Fatalities webpage. Bureau of Labor Statistics, U.S. 

Department of Labor. Accessible at http://www.bls.gov/iif/.

7. Chapter 81, Transportation Management Plans. Indiana Design Manual. Indiana 

Department of Transportation. 2009.

8. Traffic Management in Work Zones: Interstates and Other Freeways. Policy No. 

516-003. Ohio Department of Transportation. July 2000.

9. Work Zone Safety Performance Measures Guidance Booklet. Developed by the 

American Traffic Safety Services Association for the FHWA Work Zone Safety Grant 

Program, U.S. Department of Transportation, Washington, DC. No Date. 

Accessible at 

http://www.workzonesafety.org/fhwa_wz_grant/atssa/atssa_wz_performance_measu

res.

10.Highway Mobility Operations Manual. Oregon Department of Transportation. July 

2005. 
52

11.Travel Time Reliability: Making it There on Time, All the Time. Report No. FHWAHOP-06-070. FHWA Office of Operations, Washington, DC. Accessible at 

http://ops.fhwa.dot.gov/publications/tt_reliability/brochure/

12.Fatality Assessment and Control Evaluation (FACE) Program. National Institute of 

Occupational Safety and Health, Centers for Disease Control, Morgantown, West 

Virginia. Accessible at http://www.cdc.gov/niosh/face/.

13.Chandler, B., K. Beasley, and J. Rephlo. National Evaluation of the SafeTrip-21 

Initiative: I-95 Corridor Coalition Test Bed, Final Evaluation Report: North Carolina 

Deployment of Portable Traffic-Monitoring Devices. Report No. FHWA-JPO-10-

0058. FHWA, U.S. Department of Transportation, Washington, DC, June 2010. 

14.Work Zone Travel Time System. Intelligent Transportation Systems in Work Zones: 

A Case Study. Report No. FHWA-HOP-04-032. FHWA, U.S. Department of 

Transportation, Washington, DC, October 2004

15.Haseman, R.J., J.S. Wasson, and D.E. Bullock. Real Time Measurement of Work 

Zone Travel Time Delay and Evaluation Metrics Using Bluetooth Probe Tracking. In 

Transportation Research Record 2169. TRB, National Research Council,

Washington, DC, 2010, pp. 40-53.

16.Fontaine, N.D., and B.L. Smith. Probe-Based Traffic Monitoring Systems with 

Wireless Location Technology: An Investigation of the Relationship between System 

Design and Effectiveness. In Transportation Research Record 1925. TRB, National 

Research Council, Washington, DC. 2005. pp. 3-11.

17.Memmott, J.L. and C.L. Dudek. A Model to Calculate the Road User Costs at Work 

Zones. Report No. FHWA/TX-83/20+292-1. Texas Transportation Institute, College 

Station, TX, September 1982.

18.Highway Capacity Manual. TRB, National Research Council, Washington, DC. 

2000.

19.Key Steps and Critical Practices in Performance-Based Management. Operations 

Performance Measurement Program. FHWA, U.S. Department of Transportation, 

Washington, DC. Accessible at 

http://www.ops.fhwa.dot.gov/perf_measurement/fundamentals/key_steps.htm.

20.Executive Guide: Effectively Implementing the Government Performance and 

Results Act. Report GAO/GGD-96-118. U.S. Government Accounting Office, 
53

Washington, DC. June 1996. Accessible at http://www.access.gpo.gov/cgibin/getdoc.cgi?dbname=gao&docid=f:gg96118.txt.pdf.

21.Tarnoff, P.J., S.E. Young, J. Crunkleton, and N. Nezamuddin, Guide to 

Benchmarking Operations Performance Measures. Draft Final Report, NCHRP 

Project 20-7. TRB, National Research Council, Washington, DC. January 2008. 

Accessible at http://www.catt.umd.edu/documents/final_report_compiled_v26.pdf.

22.Best Practices in Project Delivery Management. NCHRP Domestic Scan Team 

Report 07-01, Project 20-68A. TRB, National Research Council, Washington, DC. 

October 2009. Accessible at 

http://onlinepubs.trb.org/onlinepubs/nchrp/docs/nchrp20-68A_07-01.pdf.

55

APPENDIX: DATA COLLECTION FORM FOR MANUAL 

DOCUMENTATION OF QUEUE LENGTHS AND DURATION
56
57

Project: _________________________________________________________________________________________

Date

Times of Work Activity Times of Work Activity with

Lane Closures Queuing During Work Activity with Lane Closures

Time

Begin

Time

End

Dir of

Travel

Loc of

Work

Time

Begin

Time 

End

Dir of 

Travel

Loc of 

Closure

# Lns

Clsd

Time 

Q 

Starts

Time 

Q 

Ends

Q

Lngth

Hr 1

Q

Lngth

Hr 2

Q

Lngth

Hr 3

Q

Lngth

Hr 4

Q

Lngth

Hr 5

Q

Lngth

Hr 6

Notes:

Estimates of queue lengths approximately every hour are desired. However, the time can be adjusted slightly as necessary, as 

long as the reporting time is noted.

Locations of work and lane closures can be noted using mile markers, stations, etc. 


U.S. Department of Transportation

Federal Highway Administration

Office of Operations

1200 New Jersey Ave., SE

Washington, D.C. 20590

www.fhwa.dot.gov/workzones

FHWA-HOP-11-033