Traffic Safety Evaluation of Nighttime and Daytime Work Zones (2008) / Chapter Skim
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Pages 14-33
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From page 14... ...
The relationships are depicted as nonlinear, reflecting expectations that the effects of congestion and queues significantly add to the crash risk as volumes increase. The potential for the increased crash costs at night work operations to exceed those at daytime work operations is also implied at very high traffic volume levels since temporary lane closures on very high-volume facilities can still create traffic and congestion even at night.
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From page 15... ...
Theorized relationships between increased traffic crash risk and roadway traffic demand at nighttime and daytime work operations that require temporary lane closures.
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From page 16... ...
, information concerning lane closures, or both. Researchers contacted the Ohio DOT to obtain more detailed hard-copy diaries but found that the hard-copy diaries did not contain any additional information.
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From page 17... ...
Similarly, crash risk increases during periods of work activity but with no temporary lane closures was assumed to reflect the combined effects of the geometric changes/work zone design decisions and distractions and turbulence caused by work activities adjacent to the travel lanes. Finally, the increase in crash risk during periods of work activity with temporary lane closures represented the combined effect of geometric changes/work zone design decisions, work activity distractions and turbulence, and additional traffic turbulence caused by the temporary roadway capacity restrictions.
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From page 18... ...
The ratio of the actual number of crashes occurring during the operation of the work zone to the EB estimate is then used to estimate the incremental effect of the 18 Work Zone Analysis Period Ef fe ct o f T em po ra ry G eo m et ri c a nd W or k Zo ne D es ig n In flu en ce s o n Sa fe ty Ef fe ct o f O ffTr av el La ne W or k A ct iv ity D ist ra ct io ns a nd D isr up tio ns o n Sa fe ty Ef fe ct o f T ra ffi c D isr up tio ns d ue to Te m po ra ry R oa dw ay C ap ac ity R ed uc tio ns o n S af et y When Work Zone Inactive and No Temporary Lane Closures X When Work Zone Active and No Temporary Lane Closures X X When Work Zone Active and Temporary Lane Closures Present X X X Table 11. Relationship between work zone analysis periods and influences on work zone safety.
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From page 19... ...
The differential crash costs per unit duration of work activity or inactivity (with and without temporary lane closures) per mile of work zone were computed and modeled as a function of AADT.
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From page 20... ...
PDO Crashes Figure 3. Index of change for injury and PDO crashes during periods of work activity with temporary lane closures in place.
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From page 21... ...
Index of change for injury and PDO crashes during periods of work activity but no temporary lane closures in place.
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From page 22... ...
Index of change for injury and PDO crashes when work area was inactive (no temporary lane closures in place)
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From page 23... ...
This would imply that the increase in crash risk when the work zone is active but lane closures are not present should be lower than when work activity is occurring and temporary lane closures are present. Although the crash ratios for daytime operations with and without temporary lane closures are consistent with this hypothesis, the results of this analysis indicate that working at night outside the travel lanes may have more substantial impacts on motorist safety than was known previously.
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From page 24... ...
Table 15. Index of change for injury and PDO crashes by AADT range during periods of no work activity and no temporary lane closures.
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From page 25... ...
The differences between working at night versus working during the day on a project task that does not require temporary lane closures are less clear. Using the same California SPFs as before, researchers applied the appropriate percentage crash rate increases for this condition from Table 14 to estimate the total increased crash costs on a per 100 work hours per mile of work zone basis.
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From page 26... ...
. Types of Crashes Occurring during Nighttime and Daytime Work The preceding section examined the differences in work zone crash risk and crash costs between daytime and nighttime work for comparable periods of work activity and inactivity with and without lane closures present.
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From page 27... ...
The rear-end crash percentages during periods of active work with and without temporary lane closures are provided in Figure 10 and Figure 11 for daytime and nighttime, respectively. During the day, a significant increase in rear-end crashes is evident at AADT levels below 100,000 vpd when the work zone is active regardless of whether or not a lane closure is present.
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From page 28... ...
0% 10% 20% 30% 40% 50% 60% 70% 80% 0 50000 100000 150000 200000 Roadway AADT Pe rc en t o f C ra sh es T ha t I nv ol ve a R ea rEn d Co lli si on Work Zone Active with Temporary Lane Closures Work Zone Active without Temporary Lane Closures Work Zone Inactive Figure 10. Comparison of work activity and roadway AADT to rear-end collision percentages, daytime work periods.
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From page 29... ...
Figure 12 presents fixed-object crashes compared to AADT, and it is apparent that fixed-object crashes for both the before and inactive periods decrease markedly 29 0% 10% 20% 30% 40% 50% 60% 70% 80% 0 50000 100000 150000 200000 Roadway AADT Pe rc en t o f C ra sh es T ha t I nv ol ve a R ea rEn d Co lli si on Work Zone Active with Temporary Lane Closures Work Zone Active without Temporary Lane Closures Work Zone Inactive Figure 11. Comparison of work activity and roadway AADT to rear-end collision percentages, nighttime work periods.
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From page 30... ...
• The actual change in crash risk in these work zones varied substantially from project to project, even when stratified on the basis of time period (daytime or nighttime) and work condition (no work activity, active work without lane 30 Time of Day Active Work with Lane Closures Active Work without Lane Closures No Active Work, No Lane Closures No Work Zone Present Daytime Periods 20.3% 10.3% 15.9% 15.3% Nighttime Periods 22.8% 21.0% 31.9% 32.4% Table 19.
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From page 31... ...
0% 10% 20% 30% 40% 50% 60% 70% 80% 0 50000 100000 150000 200000 Roadway AADT Pe rc en t o f C ra sh es T ha t I nv ol ve a F ix ed O bje ct Co llis ion Work Zone Active with Temporary Lane Closures Work Zone Active Without Temporary Lane Closures Work Zone Inactive Figure 14. Comparison of work activity and roadway AADT to fixed-object collision percentages, nighttime work periods.
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From page 32... ...
• The increase in crash costs when the work is inactive and no temporary lane closures are required is slightly higher at night than during the day across the range of AADTs examined, although these differences are not statistically significant. For both daytime and nighttime periods, the increased crash costs when work zones are present but with no work activity are much less, at any AADT, than when work is active, whether or not a lane closure is present.
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From page 33... ...
No clear trends exist in the percentages across the work conditions examined in either time period. During the day, the percentages range between 14 and 21 percent; at night, the percentages range between 23 and 28 percent.
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