1. Executive Summary
In a study sponsored by the Federal Highway Administration (FHWA), researchers conducted a survey of 789 work zones posted on 13 state road closure and construction websites during a two-week snapshot of the peak summer roadwork season in 2001. The goal of this study was to catalogue the work zone related content of these websites and explore the use of the data obtained to estimate national-level statistics such as the number of miles on the National Highway System (NHS) with work zones during the peak of the summer roadwork season.
The number of work zones as well as the data reported by each state varied widely, because states have different criteria for selecting work zones for posting on the web. Some states reported many work zones but provided fewer data elements while others reported on fewer work zones but provided more data elements. Attributes of roadwork that are determined early and are unlikely to change were more frequently reported, e.g., project duration and purpose (Table 1(a)). Less frequently reported elements included attributes that are difficult to predict in advance or those that change frequently (such as work zone length, and the time-of-day when lane closures occur). Predictions of delay beyond a simple advisory are rare, particularly quantitative estimates of delay.
| Work Zone Attribute | Reporting Frequency |
|---|---|
| Purpose | 78% |
| Project Duration | 71% |
| Number of Lanes Closed | 37% |
| Delay (Advisory) | 26% |
| Closure Duration | 22% |
| Length | 18% |
| Delay (Quantitive) | 7% |
| Cost | 4% |
For the work zones that reported particular attributes, various statistics could be drawn from the data obtained. For example, looking at reported lane closures by time of day, we estimated that 58% of work zones were active or had lane closures primarily during daylight hours, 33% were primarily night work, and 9% were active nearly around the clock (Table 1(b)). The average work zone had lane closures for 11 hours a day and occupied 6.8 miles of roadway for an average of 125 days.
The most frequent reported purposes for work zones were bridge-related roadwork (28%) and pavement operations (24%). Pavement operations had a much higher frequency of night activity: two-thirds of all resurfacing/paving activity was conducted as night work.
| Reported Time of Day | Frequency |
|---|---|
| Day Work | 58% |
| Night Work | 33% |
| Continuous Work | 9% |
From the data obtained, it was possible to construct rough estimates of several national-level statistics. The 13 states in our sample contain 24.5% of the total miles of NHS. Excluding work zone records associated with non-NHS facilities, we estimated that there were 3,110 work zones on the National Highway System at any time during the peak summer 2001 roadwork season. Similarly, we estimated that these work zones on the NHS covered 20,876 miles of roadway, or 12.8% of the 163,734 miles of NHS-designated roadway.
Further, based on lane closure data we estimated that the work zone activity on the NHS resulted in a loss of over 60 million vehicles of capacity per day. Between 9 AM and 10 AM, the most frequent hour of roadwork activity, the collective impact of work zones on the NHS was estimated as equivalent to 2,672 lane-miles of freeway, or roughly the carrying capacity associated with one direction (three lanes) of a six-lane interstate connecting Washington, DC to St. Louis, MO. National estimates of delay and productivity impacts could not be determined.
