The National Academies Press

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From page 37... ... 37 S E C T I O N 4 This section of the report describes the field data collection methodology and presents the results of the interdisciplinary field reviews conducted as part of the current research. The section includes an overview of the interdisciplinary field review approach, a description of the site selection activities, a description of the interdisciplinary investigations, and a summary of the results obtained. Read the entire page →
From page 38... ... 38 (i.e., the roadway in one direction of travel on a divided highway) , generally at least 1.6 km (1.0 mi) Read the entire page →
From page 39... ... 39 These interdisciplinary site reviews at locations with a high frequency of median-related or cross-median crashes lead the researchers to identify factors related to high driverworkload conditions, such as the presence of interchange ramps, horizontal curves, lane drops, or combinations of these factors. These reviews were conducted in an unbiased manner, and the study team was careful that their findings were not shaped by preconceptions as to which factors might prove to be important. Read the entire page →
From page 40... ... 40 Roadway Type • Rural freeways: 69.9 miles (72 percent) ; • Rural divided nonfreeways: 11.1 miles (11 percent) Read the entire page →
From page 41... ... 41 Site number County Route Direction of travel Length (mi) Roadway type Median typea Median width (ft) Read the entire page →
From page 42... ... 42 Site number Driver workload level Contributing factors CA01 Low-Moderate On-ramp Long tangent On-ramp located after 12-mi level tangent CA02 Low-Moderate Horizontal curve Truck stopping area on wide shoulder CA04 Low-Moderate Off-ramp On-ramp Bridge CA05 High On-ramp Upgrade Bridge On-ramp on upgrade with short acceleration lane upstream of bridge Low-speed merge due to upgrade CA07 Moderate-High On-ramp Off-ramp Closely spaced on-ramp followed by off-ramp (short weaving area) Closely spaced on-ramps CA10 Low Off-ramp CA11 Moderate-High On-ramp Off-ramp Closely spaced on-ramp followed by off-ramp (short weaving area) Read the entire page →
From page 43... ... 43 Site number Driver workload level Contributing factors MO09 Very Low No contributing factors noted MO10 Moderate Horizontal curve Off-ramp On-ramp Trees block sight-distance to on-ramp MO11 High Off-ramp On-ramp Horizontal curve Downgrade On-ramp with multilane entrance (three entering lanes) on slight curve on downgrade (curve has influence even though slight) Read the entire page →
From page 44... ... 44 Site number Driver workload level Contributing factors WA03 Very High Tunnel HOV lane Off-ramp Closely spaced off-ramps Off-ramp with multilane exit Off-ramp with lane-drop exit Horizontal curve WA04 High Downgrade Horizontal curve On-ramp Off-ramp Downgrade ending in horizontal curve Left-side on-ramp Closely spaced on-ramp followed by off-ramp (one left-side, one right-side) WA05 High On-ramp Off-ramp Left-side off-ramp Off-ramp with lane-drop exit Horizontal curve Downgrade Sag vertical curve On-ramp with merge area in sag vertical curve WA06 High Downgrade On-ramp Off-ramp Off-ramp with multilane exit Off-ramp with lane-drop exit Bridge Closely spaced on-ramp followed by off-ramp with two-lane lane-drop exit WA07 Moderate Narrow bridge Off-ramp Downgrade Off-ramp just beyond narrow bridge on downgrade Off-ramp with multilane exit On-ramp WA08 Low-Moderate At-grade intersections WA10 Moderate Downgrade On-ramp Sharp horizontal curve On-ramp with high truck volume Sharp horizontal curve on downgrade Sag vertical curve Upgrade WA11 Moderate On-ramp Horizontal curve Downgrade Crest vertical curve On-ramp on mainline curve on downgrade Upgrade Horizontal curve at crest vertical curve Long horizontal curve (90o turn) Read the entire page →
From page 45... ... 45 Site number Driver workload level Individual contributing factors CA01 Low-Moderate On-ramp Long tangent CA02 Low-Moderate Horizontal curve Truck stopping area on wide shoulder CA04 Low-Moderate Off-ramp On-ramp Bridge CA05 High On-ramp Upgrade Bridge CA07 Moderate-High On-ramp Off-ramp CA10 Low Off-ramp CA11 Moderate-High On-ramp Off-ramp Mainline lane drop CA13 High On-ramp Off ramp Sag vertical curve CA14 Moderate-High On-ramp Off-ramp Bridge CA15 Moderate Off-ramp On-ramp MO01 Low Downgrade Bridge Horizontal curve MO02 Moderate Horizontal curve Upgrade Off-ramp On-ramp Crest vertical curve MO03 Moderate Horizontal curve At-grade intersections MO04 Low Horizontal curve Long tangent At-grade intersections MO05 Low-Moderate On-ramp Horizontal curve Downgrade MO06 Low Horizontal curve Downgrade MO07 Low-Moderate Off-ramp On-ramp MO08 Very Low No contributing factors noted MO09 Very Low No contributing factors noted MO10 Moderate Horizontal curve Off-ramp On-ramp MO11 High Off-ramp Off-ramp with lane-drop exit On-ramp Horizontal curve Downgrade Bridge MO12 High Off-ramp On-ramp OH01 Low Bridge OH02 Low No contributing factors noted OH03 Low No contributing factors noted OH04 High On-ramp Off-ramp Downgrade Bridge Table 4-3. Summary of driver workload levels and individual contributing factors by site. Read the entire page →
From page 46... ... 46 Site number Driver workload level Individual contributing factors OH07 Moderate Off-ramp On-ramp Bridge Downgrade OH08 Moderate Upgrade Bridge Horizontal curve Crest vertical curve Off-ramp On-ramp OH09 Low No contributing factors noted OH10 Moderate Sharp horizontal curve Off-ramp OH11 Low-Moderate Off-ramp On-ramp Horizontal curve OH12 Moderate Off-ramp Horizontal curve OH13 Moderate-High Bridge On-ramp Downgrade WA02 Low-Moderate Off-ramp On-ramp Bridge WA03 Very High Tunnel HOV lane Off-ramp Off-ramp with lane-drop exit Horizontal curve WA04 High Downgrade Horizontal curve On-ramp Off-ramp WA05 High On-ramp Off-ramp Off-ramp with lane-drop exit Horizontal curve Downgrade Sag vertical curve WA06 High Downgrade On-ramp Off-ramp Off-ramp with lane-drop exit Bridge WA07 Moderate Narrow bridge Off-ramp Downgrade On-ramp WA08 Low-Moderate At-grade intersections WA10 Moderate Downgrade On-ramp Sharp horizontal curve Sag vertical curve Upgrade WA11 Moderate On-ramp Horizontal curve Downgrade Crest vertical curve Upgrade Truck stopping area on wide shoulder OH05 Low Bridge OH06 High On-ramp Horizontal curve Major merge area (two freeways merge) Mainline lane drop Table 4-3. Read the entire page →
From page 47... ... 47 Site number Driver workload level Individual conributing factors WA12 Moderate-High Steep downgrade Horizontal curve Site begins downstream of an on-ramp WA13 High Upgrade Downgrade Sharp horizontal curve Off-ramp WA14 High Horizontal curve Off-ramp Downgrade Note: This table lists all contributing factors whether those factors contribute to high driver-workload individually or in combination with other factors. Table 4-3. Read the entire page →
From page 48... ... 48 entered the median was trying to avoid collision with another vehicle, and other crashes in which vehicle–vehicle interactions contributed to the crash. Crashes that involve a vehicle swerving to avoid being cut off by another vehicle changing lanes or swerving to avoid another vehicle stopping suddenly were classified as vehicle-interaction crashes. Read the entire page →
From page 49... ... 49 Description of contributing factor Total Contributing factors by driver workload level Very low Low Lowmoderate Moderate Moderatehigh High Very high RAMPS 80 0 4 8 22 9 34 3 On Ramps 44 0 2 5 14 5 18 0 On ramp 22 2 3 9 1 7 Closely spaced on ramps 5 2 3 Left-side on-ramp 2 2 Multilane entrance 1 1 Merge area in sag vertical curve 1 1 Downstream of on-ramp 1 1 High truck volume on on-ramp 2 1 1 Major merge 1 1 Short acceleration lane 1 1 Low-speed merge due to curve on ramp 3 1 2 Low-speed merge due to mainline curve 1 1 Low-speed merge due to short ramp 1 1 Low-speed merge due to grade 1 1 Limited sight-distance to on ramp 2 2 Off Ramps 29 0 2 3 8 1 12 3 Off ramps 20 2 3 7 8 Closely spaced off ramps 1 1 Multilane exit 2 1 1 Off-ramp with lane drop 3 2 1 Left-side off ramp 1 1 Short deceleration lane 1 1 Limited sight-distance to off ramp 1 1 On- and Off-Ramps 7 0 0 0 0 3 4 0 Closely spaced on- and off-ramp 7 3 4 HORIZONTAL CURVES 25 0 4 4 10 1 5 1 Horizontal curves 17 4 4 5 1 2 1 Sharp horizontal curve 3 2 1 Long horizontal curve 1 1 Sequence of reverse curves 1 1 Downgrade ending in curve 1 1 Crest vertical curve on horizontal curve 2 2 VERTICAL ALIGNMENT 21 0 2 1 8 2 8 0 Downgrade 13 2 1 4 1 5 Steep downgrade 1 1 Upgrade 5 3 2 Sag vertical curve 2 1 1 OTHER 24 0 5 3 7 2 5 2 Bridge 12 4 1 2 1 4 Narrow bridge 1 1 At-grade intersection 3 1 1 1 At-grade intersection on curve 1 1 Mainline lane drop 2 1 1 Tunnel 1 1 HOV lane 1 1 Widened shldr/truck stopping area 3 1 2 Total Observations 150 0 15 16 47 14 52 6 Percentage of Observations 0.0 10.0 10.7 31.3 9.3 34.7 4.0 Table 4-5. Frequency distribution of individual and combined contributing factors. Read the entire page →
From page 50... ... 50 weather in California in contrast to the other three states, and much more snow, ice, and slush in Ohio and Washington than in Missouri. Table 4-8 compares the mean number of days with precipitation for California, Missouri, Washington, and Ohio based on data from the U.S. Read the entire page →
From page 51... ... 51 Site number Number of crashes in a 5-year period by crash type and pavement surface condition Length (mi) Directional AADT (veh/day) Read the entire page →
From page 52... ... 52 were only half as likely to occur on wet and snow-covered roads as on dry roads. If it was assumed that road condition was affected the entire day on days in which 0.01 inch of precipitation or more was recorded, one would expect about 30 percent of the vehicle-interaction crashes to occur on wet and snow-covered roads. Read the entire page →
From page 53... ... Site number Driver workload Number of crashes in a 5-year period by crash type and pavement surface condition Length (mi) Directional AADT (veh/day) Read the entire page →
From page 54... ... Site number Driver workload Number of crashes in a 5-year period by crash type and pavement surface condition Length (mi) Directional AADT (veh/day) Read the entire page →
From page 55... ... 55 cle striking an object, overturning, or coming to rest before crossing the median. Indeed, only 12 percent of the 97.4 miles of interdisciplinary field review sites had traversable medians where it is physically possible to cross the median without encountering a median barrier, fixed objects, or nontraversable terrain. Read the entire page →

From page 37...

... 37 S E C T I O N 4 This section of the report describes the field data collection methodology and presents the results of the interdisciplinary field reviews conducted as part of the current research. The section includes an overview of the interdisciplinary field review approach, a description of the site selection activities, a description of the interdisciplinary investigations, and a summary of the results obtained.