Section 1

Work Zone and Traffic Characteristics

1.1 Overview

This manual provides guidelines and procedures to compute Road User Costs via a modeled approach that provides the analyst with consistent and quantifiable results. Road User Costs are directly related to the traffic demand, facility capacity, and the timing, duration and frequency of work zone induced capacity restrictions. The reliability of Road User Cost calculations is greatly dependent on good 24-hour traffic counts for weekday and weekend traffic and the percent of passenger cars and trucks in the traffic stream.
This manual will familiarize the analyst with work zone and traffic characteristics, explain the possible work zone related road user cost components that can occur, and provide a step by step procedure to determine road user costs. Example problems, default hourly traffic percentages, and computation worksheets are also provided to aid the analyst with the road user cost computations.
The road user costs incurred by the traveling public during project improvements can be extremely high. This manual provides a reasonable measurement of costs incurred by the traveling public to be paid in the form of Liquidated Damages, in lieu of timely performance by the contractor.

1.2 Purpose

Road User Costs in the work zone are added vehicle operating costs and delay costs to highway users resulting from construction, maintenance, or rehabilitation activity. They are a function of the timing, duration, frequency, scope, and characteristics of the work zone; the volume and operating characteristics of the traffic affected; and the dollar cost rates assigned to vehicle operations and delays.
As long as work zone capacity exceeds vehicle demand on the facility, road user costs are normally not a serious cost to the traveling public. Under such circumstances, the roadway operates under free flow conditions and road user costs are dominated by delay costs in traveling the work zone.
When vehicle demand on the facility exceeds work zone capacity, the facility operates under forced flow conditions and road user costs can be immense. Queuing costs can account for over 90% of road user costs with the majority of the cost being the delay time of crawling through long slow moving queues.
Designers should consider road user costs when determining the most appropriate construction staging and final design. This should be done early in the design process while there is still flexibility in the design. The optimal design will mitigate or avoid disruptions before they can be created. In addition to considering road user costs for the present construction needs, the analysis procedure provides the tools to determine future road user costs based on future construction needs. By understanding the major factors influencing road user costs, the designer can take steps to minimize the effect of planned future rehabilitation activities on highway users.
Alternatives available to reduce work zone related road user costs include carefully selecting the preferred scheme and frequency of rehabilitation activities, restricting the allowable work hours to avoid queuing, adding capacity prior to the development of large traffic demands, accelerating contractor production rates to reduce the overall work zone duration, and utilizing alternative project delivery methods. For some projects, improvements could include enhanced mass transit services, improvements to other routes, coordination with other agencies, and public outreach.
The quantification of road user costs in both time and money provides the designer with a valuable decision making tool. The examples in this manual illustrate many practical and real life applications.

1.3 Benefits

Road User Costs play an important role in computing Liquidated Damages. The contractor’s failure to complete a contract or reopen a lane of traffic on time results in damages in terms of delay and cost to the motoring public and the Department. The procedures in this manual will establish how to calculate and apply these damages. Desirably, these damages will never be imposed because it is preferable to avoid high road user costs by adhering to the completion dates and allowable work hours provided in the contract. The methods of computing liquidated damages have taken into account input by the Construction Industry and reflect that road user costs are in fact real, but difficult to accurately calculate given the many factors involved and the different variables that exist on a given day in the life of a construction project.
Road user costs can be used in Benefit/Cost ratios, Life Cycle Cost Analyses, and selecting the most appropriate project delivery method (Incentive/Disincentive, A+B Bidding, etc.). Road User Costs are not direct costs to the Department’s budget, but they do directly affect the public it serves. This manual is an excellent tool in helping to determine the appropriate capital investment on a project.

1.4 Definitions

Work Zone is defined in the Highway Capacity Manual as an area of a highway in which maintenance and construction operations are taking place that impinge on the number of lanes available to traffic or affect the operational characteristics of traffic flowing through the area.
Road User Costs in the work zone are added vehicle operating costs, delay costs, and crash costs to highway users resulting from construction, maintenance, or rehabilitation activity.

1.5 Work Zone Characteristics

In order to calculate work zone related road user costs the characteristics of the work zone must be defined. Work zone characteristics of concern include such factors as work zone length, number and capacity of lanes open, duration of lane closures, timing (hours of the day and days of the week) of lane closures, posted speed, and the availability and traffic characteristics of alternative routes. The strategy for the maintenance of traffic should include any anticipated restrictions on contractor’s or maintenance force’s hours of operations or ability to establish lane closures.
Each work zone established over the analysis period can have different impacts on traffic flow and the associated user costs. Whenever characteristics of the work zone or the characteristics of the affected traffic change, a separate work zone must be defined and evaluated as a separate event.
The duration of a work zone (i.e. the overall length of time a facility or portion of a facility is out of service) can range from sporadic daily lane closures for maintenance to several months for bridge deck replacements.

1.6 Traffic Diversion

Traffic demand is generally determined based on the need to use the facility. Traffic volume during work zone operations may or may not be the same. Some portion of the traffic normally wanting to use the facility may divert to other routes when work zones are established.
Vehicles use a given facility because it offers, what the vehicle operators perceive to be, the least expensive combination of vehicle operating and time delay costs, consistent with safety requirements. When faced with restricted flow, or even the anticipation of restricted flow, vehicle operators who normally use a facility will exercise one of several options. The potential vehicle operator responses are categorized below.

Hang Toughers - This group continues to use the facility as they always have. They are primarily users with little, or no, option. They (1) must make the trip, (2) they must make it at a specific time, and (3) either don’t know of or don’t have alternative routes or modes to choose from. These users pay the full price of the work zone and have little effect on other facilities in the corridor. In rural areas, the predominate choice of through traffic will be to tough it out, as these users generally must make the trip and do not have available alternative routes unless formal detours are established.
Time Shifters - Time Shifters have the “luxury” to travel on the facility or other route at a different time, generally a time well outside of the restricted flow period. These users lessen their impact by sharing the impact with other vehicles by “invading” their time slot. These users also have little effect on other facilities in the corridor, but do impact hourly traffic distribution.
Detourees - Detourees either seek out and use alternate routes, or are forced to negotiate detours established by the highway agency. These operators also lessen their impact by sharing the impact with other vehicles by “invading” their routes. They tend to trade off anticipated time delay for additional travel distances and associated vehicle operating costs. In urban areas this could include users who switch modes. Detourees can have significant impact on overall road user costs of alternative routes.
Trip Swappers - Trip swappers have the “luxury” of totally abandoning the trip or seeking other destinations when the cost, in terms of time and money, becomes too great. Historically, this group consists primarily of shopping and social/recreational trip makers. While their behavior may diminish the road user costs impact in the work zone they adversely impact businesses along the route in question. More recent trends in people working out of the home and telecommuting may have a significant effect on work trips in the future.
In simple cases, where either work zone disruption is tolerable or alternative routes are limited, the estimated Average Daily Traffic (ADT) during the duration of the work zone can be anticipated to continue on the facility and the work zone analysis can be limited to the existing facility.
In more complex situations where existing traffic would face intolerable work zone disruptions, it is entirely possible that total travel demand and hourly distribution on the facility may change when the work zone is established. When demand changes, the road user cost analysis may have to expand beyond the existing facility and include road user costs on major alternative routes. When preliminary analyses of travel demand show that work zone related road user costs are unreasonably high, allowable work hours may need to be restricted, early contract completion incentives may be appropriate, or an alternative design may need to be considered.

1.7 Traffic Characteristics

Road user costs are directly dependent on the volume and operating characteristics of the traffic on the facility. Each construction, maintenance, and rehabilitation activity generally involves some temporary impact on traffic using the facility. The impact can vary from insignificant for minor work zone restrictions on low volume facilities to highly significant for major lane closures on high volume facilities.
The major traffic characteristics of interest for each work zone include such factors as the overall projected Average Daily Traffic (ADT) volumes, the associated 24-hour hourly traffic distributions, and the vehicle classification distribution within the traffic stream. Each of the major traffic characteristics is discussed in the sections that follow.

1.8 Average Daily Traffic (ADT)

Current weekday and weekend ADT volumes can be obtained from the traffic monitoring section. When using projected ADT volumes, it is generally assumed traffic patterns remain the same. However, consideration should be given as to whether traffic using the facility will continue to use the facility when work zones are established and traffic flow is restricted.

1.9 Hourly Traffic Distribution (By Direction)

The 24-hour hourly traffic distribution during work zone operations is essential to be able to compare the unrestricted demand on the facility with the facility’s ability to carry that traffic through the work zone. On all routes, distinctions between weekday and weekend traffic hourly distributions are important. Furthermore, when work zones are proposed on recreational routes during seasonal peak periods, seasonal ADT traffic distribution is extremely important. The New Jersey Department of Transportation has developed average hourly traffic percentages for various functional classes of roadway which are provided in Table 3.1.

1.10 Vehicle Classifications

Road user costs are a composite of costs of all affected highway users. Highway users are not a homogeneous group. They include commercial and non-commercial vehicles ranging from motorcycles and passenger cars through multi-trailer trucks. The FHWA Traffic Monitoring Guide, Third Edition (February 1995) includes 13 different vehicle classifications which are shown in Figure 1.1. These different vehicle classes have different operating characteristics and associated operating costs. Further, the value of time differs between vehicle classes. As a result, road user costs need to be analyzed for each major vehicle class present in the traffic stream.

Figure 1.1
FHWA Vehicle Classifications

Road user cost analysis based on 13 vehicle classifications would be laborious and require extensive traffic data. For simplification and consistency with available traffic data, it is recommended to use “Car” (Classes 1-4) and “Truck” (Classes 5-13) classifications only.

Last Document Correction:
September 1, 2015