美国养护工区特征分析

2001 revealed that, in addition to all interstate and US-highway work zones, the majority of state roadways with work zones were also NHS roadways.

Based on the total number of estimated work zones in the sample states, a national

estimate is derived by dividing by the total percent of NHS roadway in the sample. For example, the twenty state sample used in the four semi-annual snapshot studies

represented 42.2% of the NHS. NHS mileage by state was obtained from .

Work Zones on the NHS

As shown in Table 3, 6,400-7,200 work zones are estimated to be on the NHS during the peak construction season (2002-2003). Note that the 2001 estimate is lower because of the pilot study’s smaller sample size. In the winter, 2,600-3,000 work zones are

estimated to be on the NHS, roughly half of the number seen during the summer peak.Multiplying these estimates of the number of work zones by the average work zone length calculated for each snapshot, one can obtain an estimate of total miles of NHS with a work zone during the two-week snapshot period in each analysis.

There are 163,732 miles of roadway on the National Highway System. Therefore, in each snapshot, the estimate of miles of NHS with a work zone is expressed as a

percentage of the over total miles of NHS. From Table 3, our estimates have ranged from 13% in the pilot 2001 study to a 21-27% range in the summer 2002-2003 snapshots. Since there are fewer work zones in the winter and they have shorter length, the percent of NHS with a work zone drops to 6.9-7.4%, roughly a third of the summer time peak value.

Capacity Impacts

States provided data on likely capacity impacts for the majority of the work zones in each snapshot. Of these, nearly all of the capacity impacts were from temporary closures of one or more lanes or complete closures of roadway facilities. A small number indicated lane narrowing or shoulder work that would have some impact on roadway ing these capacity impact indicators from the state websites, total estimated capacity loss from work zones on the NHS can be estimated. First, a baseline capacity using standard values for each facility type from the Highway Capacity Manual (2000) is established. Based on text descriptions of each work zone, each record was coded as either shoulder or indirect work, a partial closure (by number of lanes closed), or full closure. A percentage reduction in roadway capacity was estimated in each case using the HCM. From these data, an estimate of reduced capacity from all the work zones on the NHS can be generated by including factors for work zone duration.This loss of capacity is measured in vehicles, and has ranged up to 180 million vehicles per day of lost capacity (summer 2003).

A peak loss in carrying capacity during the most frequent hour of activity was also

estimatedin each snapshot, expressed in terms of a single connected work zone extending