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From page 23... ... 23 S e c t i o n 3 The objective of the field studies was to evaluate the effectiveness of a treatment (or combination of treatments) in reducing speeds through a transition zone and through the community. Read the entire page →
From page 24... ... 24 Design Guidance for High-Speed to Low-Speed transition Zones for Rural Highways site is defined as a location at which no particular speed reduction treatment was installed near the transition zone with the exception of reducing the posted speed limit. Where possible, field data were collected on multiple approaches to a community (see Figure 3-1) Read the entire page →
From page 25... ... Field Studies 25 Table 3-2. Study locations and treatment types. Read the entire page →
From page 26... ... 26 Design Guidance for High-Speed to Low-Speed transition Zones for Rural Highways (i.e., crest or sag) in the vicinity of the transition zone. Read the entire page →
From page 27... ... Table 3-4. Site characteristics of study locations within the community. Read the entire page →
From page 28... ... 28 Design Guidance for High-Speed to Low-Speed transition Zones for Rural Highways • Location A -- Community Speed: The speed at this location represents the speed of vehicles through the community. – This traffic classifier was placed approximately 750 to 1,000 feet downstream of the final speed reduction treatment or the first speed limit sign to indicate the speed limit through the community, whichever was located further downstream. Read the entire page →
From page 29... ... Field Studies 29 combinations, and reduction in posted speed limits from Location C to B and Location B to A are shown in Table 3-5. Summary speed statistics from the classifiers (box plots) Read the entire page →
From page 30... ... 30 Design Guidance for High-Speed to Low-Speed transition Zones for Rural Highways Tables 3-6 through 3-9 present basic distribution statistics for all classifier speeds collected at Locations C, B, and A for each type of treatment, respectively. These statistics include the following for each location at each site: • Posted speed limit. Read the entire page →
From page 31... ... Field Studies 31 • Mean speed. • Speed standard deviation. Read the entire page →
From page 32... ... 32 Design Guidance for High-Speed to Low-Speed transition Zones for Rural Highways At each site and classifier location, speed differences between vehicle speeds and posted speed limit were calculated (i.e., a positive difference indicates that the vehicle exceeded the posted speed limit) Read the entire page →
From page 33... ... Field Studies 33 Figure 3-6. Speed differences from posted speed limit -- welcome signs. Read the entire page →
From page 34... ... 34 Design Guidance for High-Speed to Low-Speed transition Zones for Rural Highways without regard to individual site characteristics (aside from posted speed limits) ; and, therefore, do not allow for a direct assessment of a particular treatment across sites. Read the entire page →
From page 35... ... Field Studies 35 at these upstream locations. It was determined, however, that such sites are not good candidates to include in an analysis to evaluate the effectiveness of transition zone treatments in reducing speeds. Read the entire page →
From page 36... ... 36 Design Guidance for High-Speed to Low-Speed transition Zones for Rural Highways also account for speed-limit compliance by drivers upstream, the percentage of speeds at or below speed limit at Location C was included in the model. The statistical significance of treatment, after accounting for C to B posted speed reduction and for compliance upstream was evaluated, and the results from each treatment were compared to those obtained for the non-treated sites. Read the entire page →
From page 37... ... Field Studies 37 A logistic regression model was then developed to investigate the relationship between the percentage of vehicles driving at or below the speed limit at Location B and the treatment type, posted speed limit nearest Location C, and the speed reduction from Location C to Location B The percentage of vehicles driving at or below the speed limit at Location C was also included in the model to account for speed-limit compliance behavior upstream of the transition zone. Read the entire page →
From page 38... ... 38 Design Guidance for High-Speed to Low-Speed transition Zones for Rural Highways The analysis showed that of the variables considered in the model in addition to treatment type -- speed reduction from C to B, speed limit at C, and percentage of speeds at or below the speed limit at C -- only the speed reduction was statistically significant at the 10 percent level. This model also showed that the estimated percentage of vehicles driving at or below the speed limit was considerably higher (by approximately 10 percent) Read the entire page →
From page 39... ... Field Studies 39 If speed-limit compliance were defined as driving at or below the posted speed limit + 5 mph at the exit of the transition zone, then the study data show the following, accounting for the effect of speed reduction in posted speed limits from Location C to B: • The compliance rate upstream of the transition zone had no significant effect on the compliance rate at the exit of the transition zone. • The overall treatment effect on compliance rate was significant at the 10 percent significance level. Read the entire page →
From page 40... ... 40 Design Guidance for High-Speed to Low-Speed transition Zones for Rural Highways Next, taking into account the posted speed limit at each site and location, the potential additional effect of the treatment on speed reduction from C to B was estimated. This was done by calculating the difference between each vehicle's speed and the posted speed limit at each site and each location. Read the entire page →
From page 41... ... Field Studies 41 considered in the logistic model; however, to account for the potential effect of site characteristics in the community, the inclusion of the following categorical variables was initially considered: • On-street parking -- yes (three sites) , no (12 sites) Read the entire page →
From page 42... ... 42 Design Guidance for High-Speed to Low-Speed transition Zones for Rural Highways On-street parking was confounded with treatment type and was therefore not included in the model. Also, the presence of sidewalks and that of curbs are confounded; therefore the presence of sidewalks was not considered in the model. Read the entire page →
From page 43... ... Field Studies 43 After accounting for the significant effect of posted speed limit in the community and that of the presence of curbs, it was found that, for the study sites, the type of treatment in the transition zone had no significant effect on compliance rates in the community. These compliance rates range, on average and for all site types, from 54 percent to 59 percent (using the speed limit criterion) Read the entire page →
From page 44... ... 44 Design Guidance for High-Speed to Low-Speed transition Zones for Rural Highways to B) , and 0.25 mi downstream of the transition zone into the community. Read the entire page →
From page 45... ... Field Studies 45 Focusing on the crash frequencies summarized in the "crashes/mi/yr" columns of Tables 3-15 and 3-16, it appears that treatment sites are operating as safely as expected. Only one site (NE03) Read the entire page →
From page 46... ... 46 Design Guidance for High-Speed to Low-Speed transition Zones for Rural Highways Neither analysis showed any significant treatment type or before/after treatment installation effect. The p-value for the overall treatment effect associated with the first approach was 0.16. Read the entire page →
From page 47... ... Field Studies 47 Table 3-18. Collision types by site, location, and before/after treatment at intersections. Read the entire page →
From page 48... ... 48 Design Guidance for High-Speed to Low-Speed transition Zones for Rural Highways were observed regarding the effects that installation of roundabouts, TPMs, or welcome signs have on safety. Additionally, two statistical methods were used to analyze the crash data and neither analysis approach showed any significant treatment or before/after effect. Read the entire page →

From page 23...

... 23 S e c t i o n 3 The objective of the field studies was to evaluate the effectiveness of a treatment (or combination of treatments) in reducing speeds through a transition zone and through the community.