Roundabouts in the United States (2007) / Chapter Skim
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Pages 12-22
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From page 12... ...
12 This chapter describes the process used to establish an overall inventory of roundabouts in the United States, the selection of sites for data collection, and the various types of data collected at specific sites. This database serves three major purposes: • It supports the development of United States-based safety and operational models completed as part of this project.
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Characteristics Number Percentage of total Total number 310 Setting • Urban • Suburban • Rural 103 164 16 36% 58% 6% Number of legs • 6 • 5 • 4 • 3 • 2 4 16 197 70 4 1% 5% 68% 24% 1% Number of circulating lanes • 3 • 2 • 1 5 72 213 2% 25% 73% Previous intersection • One-way stop • Two-way stop • All-way stop • Signal • None 30 49 16 14 46 19% 32% 10% 9% 30% Year created • 2000-2003 • 1995-1999 • 1994 or earlier 70 70 12 46% 46% 8% Geographic location (zip code) • Northeast (0,1)
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14 Si te ID St a te City County Intersection S et tin g Le gs La n es Sa fe ty O pe ra tio na l Sp ee d Pe de st ri a n Bi cy cl ist CA06 CA Davis Yolo Anderson Rd/Alvarado Ave U 4 1 X X CA10 CA Long Beach Los Angeles Pac Coast Hwy/Hwy 19/Los Coyotes Diag. U 4 3 X CA11 CA Modesto Stanislaus La Loma/James St./G St.
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15 Si te ID St a te City County Intersection S et tin g Le gs La n es Sa fe ty O pe ra tio na l Sp ee d Pe de st ri a n Bi cy cl e MD27 MD Millington Kent US 301 NB Ramps/MD 291 R 4 1 X MD28 MD Millington Kent US 301 SB Ramps/MD 291 R 4 1 X MD31 MD Oak Grove Pr. Georges MD 193/Oak Grove Rd U 3 1 X MD33 MD Rosemont Frederick MD 17/MD 180 R 4 1 X MD38 MD Stevensville Queen Annes MD 18/Castle Marina Rd S 4 1 X MD39 MD Temple Hills Pr.
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the control type before construction, and crash data for both the before and after periods. Crash data at these roundabouts were gathered by three primary means: • Crash records were gathered from local jurisdictions in the vicinity of all field data collection sites.
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17 Number of legs = 139 (at 39 roundabouts) Mean length of crash history = 3.8 years All Single Lane Multilane Crash Type Incidence Percentage Incidence Percentage Incidence Percentage EnteringCirculating 141 23% 40 29% 101 22% Exit-Circulating 187 31% 10 7% 177 38% Rear-End on Approach 187 31% 42 30% 145 31% Loss of Control on Approach 77 13% 42 30% 35 7% Pedestrian 5 1% 1 1% 4 1% Bicyclist 8 1% 3 2% 5 1% Sum*
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• A balance between single-lane and multilane sites so that operational characteristics of both kinds of sites could be studied • A range of other geometric conditions so that the effect of these conditions on operations could be studied • A clustering of sites so that driving time to the sites could be minimized, thus maximizing the number of sites that could be studied Table 10 shows a list of the 31 sites at which field video recordings were made during spring and summer 2003. Included in the table are the date of the site visit, the site ID, the intersection name, and the city and state in which the roundabout is located.
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• Three digital video cameras that focused on individual legs at the roundabout • Two masts, each extendable to 30 ft, to which the video cameras were attached • Four DVD-R recorders to record the video directly from the digital and omni-directional cameras at the site Figure 6 shows an omni-directional camera (on the left) and a digital camera (on the right)
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Speed Data Currently, speeds are predicted for a roundabout design by measuring speeds along the "fastest path,"as defined in FHWA's Roundabouts: An Informational Guide (1)
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A summary of all sites used for this analysis is provided in Table 11. A description and image of each leg can be found in Appendix C
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• Splitter time (difference in splitter departure and arrival times) • End time (when the crossing was completed)
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