Work Zone Mobility and Safety Program

Work Zone Road User Costs - Concepts and Applications


Abbreviated Injury Scale (AIS)

An anatomically based severity scoring scheme that classifies each injury in every region of the human body according to its relative severity on a six-point adjectival scale.

Air Pollutant Emissions

Air pollutant emissions include those emitted directly into the atmosphere, such as carbon monoxide (CO), volatile organic compounds, particulate matter (PM10), oxides of nitrogen (NOX), oxides of sulfur (SOX), and those formed in the atmosphere from the directly emitted pollutants, such as ozone and acidic depositions.

Annual Average Daily Traffic (AADT)

The total volume of traffic passing a point or segment of a highway facility in both directions for 1 year divided by the number of days in the year.

Benefit/Cost Analysis

A measure of economic value that compares the net discounted benefits of an alternative to its net discounted costs. B/C ratios greater than 1.0 indicate that benefits exceed cost.

Calendar Day

Every day listed on the calendar, regardless of whether work is accomplished or allowed by other specifications.


The maximum sustainable flow rate at which vehicles or persons reasonably can be expected to traverse a point or uniform segment of a lane or roadway during a specified time period under given roadway, geometric, traffic, environmental, and control conditions; usually expressed as vehicles per hour or passenger cars per hour.

Combination Truck

Defined as vehicle classes 8 through 13 in the FHWA Traffic Monitoring Guide. Includes vehicles consisting of two or more units, one of which is a tractor or straight truck power unit.

Comprehensive Crash Cost

Includes the intangible nonmonetary losses or consequences to individuals, families, and society over the crash victim’s expected life span, in addition to the human capital costs.

Construction Manager/General Contractor (CMGC)

A two-phase project delivery method where a construction manager, selected by an owner based on qualifications for both preconstruction and construction services of a project, will be at risk for the final cost and time of construction.

Construction Phasing

Refers to the sequencing of the aspects of a project, completing portions of the project one part at a time.

Construction Staging

Refers to how the contractor will position the equipment and materials.

Consumer Price Index (CPI)

A measure of the average change over time in the prices paid by urban consumers for goods and services.

Contract Time

The total time (calendar days, working days, or completion date) established to complete the project.

Cost of Acceleration

An additional cost incurred by a contractor for expediting the contract delivery.

Cost-Based Estimating

A method to estimate the bid cost of a work item by estimating the cost of resources (time, equipment, labor, and materials) for each task necessary to complete the work item, and then adding a reasonable amount for contractor’s overhead and profit.

Cost-Plus-Time (A+B) Bidding

A contract provision that allows both cost and time to be considered in the low bid determination. The "A" component is the traditional bid for the contract items and is the dollar amount for all work to be performed under the contract. The "B" component is the total number of calendar days the bidder stipulates will be required to complete the project. Calendar days are used to avoid any potential controversy.


A collision involving at least one moving vehicle (car, truck, etc.) and another vehicle or object.

Crash Frequency

The number of crashes normalized to the roadway segment length and time period, typically expressed as crashes per mile per year.

Crash Modification Factor

A multiplicative factor used to compute the expected number of crashes after implementing a given countermeasure.

Crash Rate

The number of crashes expected or observed along a roadway segment during a time period normalized to the roadway segment length and the traffic volume over the same period, typically expressed in terms for crashes per million vehicle miles of travel.

Crash Reduction Factor

An estimate of the percentage reduction in crashes due to a particular countermeasure.

Decision Analysis

A systematic process within which a choice among specific options will be made.

Delay Time

The additional travel time necessary to traverse the work zone or to detour around it.

Demand to Capacity Ratio

The ratio of demand flow rate to capacity for a traffic facility.


A project delivery method in which the public agency procures design and construction services from two separate entities. The agency either performs designs in-house or procures services from a private engineering services entity to perform the design work, and then makes a separate procurement with a private construction services entity to perform the construction work.


A project delivery method in which the public agency combines procurement for both design and construction services into a single contract and from the same private sector entity (the design-builder).

Detour Delay

The additional time necessary to travel the excess distance by selecting a detour route.

Detour VOC

The additional vehicle operating cost associated with the excess distance to be traveled by selecting a detour route under unrestricted or restricted conditions.

Discount Factor

A portion of road user cost savings that an owner specifies as incentive and disincentive amount for a project. The selection of this factor typically is an owner agency’s management decision by taking factors into account such as market conditions, confidence on the accuracy of WZ RUC estimates, work zone factors, and time sensitivity of project completion.

Economic Analysis Technique

The approach used in the planning process to analyze the relative costs and benefits of a potential investment. The most common include Net Present Value (NPV), Benefit/Cost (B/C) ratios, Internal Rate of Return (IRR), Modified Internal Rate of Return (MIRR), and Equivalent Uniform Annual Costs (EUAC).

Employer Costs for Employee Compensation (ECEC)

Measures employer costs for wages, salaries, and employee benefits for nonfarm private and State and local government workers.

Employment Cost Index

A measure of the average change over time in the wages, benefits, and bonuses for a specific group of occupations.

Forced Flow

A condition where a traffic flow breaks down and a queue of vehicles develops.

Free Flow

A condition where a traffic flow is unaffected by upstream or downstream conditions.

Free Flow Capacity

The maximum capacity a facility can handle under free-flow conditions.

Free Flow Speed

The average speed of vehicles over a basic freeway, multilane highway or an urban street segment without signalized intersections under conditions of low volume.

Greenhouse Gases

Include those direct emissions that are not yet recognized as an air pollutants but trap heat within the atmosphere and thus contributing undesirable climatic effects, such as carbon dioxide (CO2).

Gross Domestic Product (GDP) Implicit Price Deflator

An economic metric that accounts for inflation by converting output measured at current prices into constant-dollar GDP. The GDP deflator shows how much a change in the base year’s GDP relies upon changes in the price level.

Hourly Traffic Demand

The 24-hour hourly distribution of vehicles passing through the work zone in a single direction under normal operating conditions.

Human Capital Crash Cost

Includes the “hard dollar” costs related directly to a crash, such as property damage, medical care, compensations, and legal costs.

Incentive/Disincentive (I/D)

A contract provision which compensates the contractor for each day that identified critical work is completed ahead of schedule and assesses a deduction for each day that completion of the critical work is delayed. The primary function of an I/D provision is to motivate the contractor to complete the work on, or ahead of, schedule, and recover damages to the traveling public for late completion.


Any occurrence on a roadway that impedes the normal flow of traffic.

Interim Completion Date

A contract provision that provides a contractor with an incentive or disincentive to expedite the completion of specific portions of a contract within a set duration or by a specified date.

KABCO Injury Scale

A coding scheme designed for police officers assessing a crash scene where K, A, B, C, and O are the different levels of classification.

Lane Rental

A rental fee paid by the contractor for the time period a lane is closed to through traffic for construction activities.

Life Cycle Cost Analysis

An economic assessment of an item, area, system, or facility and competing design alternatives considering all significant costs of ownership over the economic life, expressed in equivalent dollars.

Liquidated Damages

Monetary damages recovered from the contractor to compensate the agency’s additional construction oversight costs associated with the contractor’s failure to complete the project on time.

Liquidated Savings

Under this provision, the contractor receives an incentive amount equal to the savings in the owner agency’s construction oversight costs for completing the project ahead of schedule.

Maintenance of Traffic (MOT)

A set of coordinated transportation management strategies to meet the traffic mobility and safety needs within a work zone.

Normal Operation

Reflects the condition during which a facility is free of construction, maintenance, and/or rehabilitation that restrict the capacity of the facility.

No-Excuse Incentives (also called Locked Incentives)

An incentive paid to the contractor to complete a phase of work or the entire project on or before a firm completion date specified in the contract. There are no excuses, such as weather delays, for not meeting the completion date. No disincentives (other than normal liquidated damages) apply for not meeting the target date.

Passenger Car

Defined as vehicle classes 1 through 3 in the FHWA Traffic Monitoring Guide. Includes automobiles (small, medium, or large), pickup trucks, and vans.

Passenger-Car Equivalent (PCE)

The number of passenger cars displaced by a single heavy vehicle of a particular type under specified roadway, traffic, and control conditions.

Producer Price Index (PPI)

A measure of the average change over time in the selling prices received by domestic producers of goods and services. The PPI measures price change from the perspective of the seller. This contrasts with other measures, such as the Consumer Price Index (CPI), that measure price change from the purchaser’s perspective.


A line of vehicles, bicycles, or persons waiting to be served by the system in which the flow rate from the front of the queue determines the average speed within the queue. Slowly moving vehicles or people joining the rear of the queue usually are considered part of the queue. The internal queue dynamics can involve starts and stops. A faster-moving line of vehicles often is referred to as a moving queue.

Queue Delay

The additional time necessary to travel through the queue under restricted traffic flow.

Queue Idling VOC

The additional vehicle operating cost associated with stop-and-go driving in the queue. The idling cost rate multiplied by the additional time spent in the queue is an approximation of actual VOC associated with stop-and-go conditions. When a queue exists, stopping delay and VOC replace the free-flow speed change delay and VOC.

Reduced Speed Delay

The additional time necessary to traverse the work zone at the lower posted speed; it depends on the upstream and work zone speed differential and length of the work zone under both unrestricted and restricted (forced) traffic flow.

Significant Project

A project that, alone or in combination with concurrent projects nearby, is anticipated to cause sustained work zone impacts (or high level of disruption) that are greater than what is considered tolerable based on an agency’s policy and/or engineering judgment.

Single-Unit Truck

Defined as vehicle classes 4 through 7 in the FHWA Traffic Monitoring Guide. Includes six-tire trucks and trucks on a single frame with three or more axles.

Speed Change Delay

The additional time necessary to decelerate from the upstream approach speed to the work zone speed and then to accelerate back to the initial approach speed after traversing the work zone under unrestricted (free) traffic flow.

Speed Change VOC

The additional vehicle operating cost under unrestricted conditions associated with decelerating from the upstream approach speed to the work zone speed and then accelerating back to the approach speed after leaving the work zone.

Stopping Delay

The additional time necessary to come to a complete stop from the upstream approach speed (instead of just slowing to the work zone speed) and the additional time to accelerate back to the approach speed after traversing the work zone under restricted traffic flow.

Stopping VOC

The additional vehicle operating cost under restricted conditions associated with stopping from the upstream approach speed and accelerating back up to the approach speed after traversing the work zone.

Transportation Management Plan (TMP)

A plan that lays out a set of coordinated strategies and describes how they will be used to manage the work zone impacts of a road project. Strategies include temporary traffic control measures and devices, public information and outreach, and operational strategies such as travel demand management, signal retiming, and traffic incident management.

Travel Delay Cost

A product of total travel delay time of all vehicles caused by work zone conditions and the value of travel time (by vehicle type).

Travel Speed

The average speed, in miles per hour, of a traffic stream computed as the length of a highway segment divided by the average travel time of the vehicles traversing the segment.

Value of Travel Time

Economic value of travel time usually expressed in terms of dollar per hour per vehicle or dollar per hour per person.

Vehicle Operating Costs (VOC)

The expenses incurred by the road users as a result of vehicle use.

Working Day

Any day on which work is planned and could be performed. Weekends and holidays frequently are excluded from a working day contract.

Work Zone

A segment of highway in which maintenance and construction operations impinge on the number of lanes available to traffic or affect the operational characteristics of traffic flowing through the segment. A work zone typically is marked by signs, channelizing devices, barriers, pavement markings, and/or work vehicles. It extends from the first warning sign or high-intensity rotating, flashing, oscillating, or strobe lights on a vehicle to the END ROAD WORK sign or the last temporary traffic control device.

Work Zone Capacity

The maximum sustainable flow rate at which vehicles can pass a given point or uniform segment of a lane or roadway in a work zone during a specified period under prevailing roadway, traffic, and control conditions. Capacity usually is expressed as passenger cars per hour per lane (pcphpl) or vehicles per hour per lane (vphpl).

Work Zone Delay Time

The additional travel time experienced by a vehicle to traverse the work zone or to detour around it.

Work Zone Mobility

Pertains to moving road users efficiently through or around a work zone area with a minimum delay compared to baseline travel when no work zone is present, while not compromising the safety of highway workers or road users. The commonly used performance measures for the assessment of mobility include delay, speed, travel time, and queue length.

Work Zone Performance Measurement

The process of collecting and using quantifiable statistical evidence to measure, monitor, and evaluate the efficiency of work zone operations.

Work Zone Performance Measures

Well defined, outcome-based conditions or response times that are used to evaluate the success of work zone policies, procedures, and performance.

Work Zone Road User Cost

An incremental cost or value incurred by highway users and the community at-large as a result of work zone activity.

Work Zone Safety

Refers to minimizing potential hazards to travelers and highway workers in the vicinity of a work zone.

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