urban roadside safety -- is there anything we can do to improve safety performance?
TRANSCRIPT
Based on Research Performed for Project NCHRP 16-04
Urban Roadside Safety
What Can We Do?
Karen K. Dixon, P.E., Ph.D. , Oregon State University
Presentation Overview
• Goals
• Background
• Case Study Review
• Corridor Study Analysis
• Recommendations
Goals
GOALS
– Goal 1: Address roadside safety in environments where the ability to provide clear roadsides is limited.
– Goal 2: Identify solutions that address common stakeholder concerns in urban environments while ensuring motorist safety.
– Goal 3: Provide guidance on the safe application of roadside elements in urban environments.
Addressing Roadside Safety
1. Keep the vehicle from leaving the
travelway.
2. Minimize the likelihood of crashes and
rollovers when a vehicle leaves the
travelway.
3. Minimize the severity of unpreventable
roadside crashes.
Source: TRB, 2003
State-of-the-Practice:
Considering Roadside Safety in
Urban Areas
Background
Current Knowledge
• At present, there is little substantive
information on the safe design of urban
roadsides:
– Most of the literature on roadside safety
focuses on rural, two-lane roadways
– Designers currently have little information on
how to evaluate the safety impacts of the
design of urban roadsides
Clear Zone vs. Operational Offset
Urban rights-of-way are often extremely restricted,
limiting the applicability of clear-zone practice –
even in suburban to urban transitions.
Survey Finding
Agree Disagree
Neither agree
nor disagree
State DOT 69% 21% 10%
City/County 85% 8% 8%
State DOT: n = 29
City-County: n = 26
“Clear zones do not and cannot exist in
urban areas due to right-of-way
limitations”
Balancing Roadside Demand
There are often competing interests
regarding the design and use of limited
urban / suburban rights-of-way.
Survey Finding
“State-adopted design guidance is sometimes
incompatible with stakeholder requests relating
to the design of community main streets.”
Agree Disagree
Neither agree
nor disagree
State DOT 52% 24% 24%
City/County 85% 0% 15%
State DOT: n = 29
City-County: n = 26
Case Study Review
Case Study Review
• Identify “beautification” or “streetscape” projects where roadside or median improvements were the focus
• Acquire crash data from before & after improvement
• Evaluate general safety of change
Summary of Case Study Locations
Phoenix, AZ (3) Sacramento, CA (3)
Eden Prairie, MN (1) Billings, MT (2)
Charlotte, NC (7) Bend, OR (2)
Portland, OR (5) Salt Lake City, UT (4)
Pursuing additional data for 3 partially complete case studies
Example Case Study:
Union Hills Drive – Phoenix, AZ
Construction Period: 7/31/01 to 2/26/03
Length of Segment: 7,931 ft
ADT: 1996 – 24,800, 1999 – 33,900
2002 – 32,700, 2005 – 29,800
Posted Speed: 45 mph
Functional Class: Major Arterial
Project Description: Add sidewalk with landscape
buffer, curb extensions
Supplemental
Information:
Road has 4 lanes (2 per
direction)
Analysis
Category
Before
(1996-
2000)
After
(2004-
2006)
Crash
Reductions
Standard
Deviation
Frequency
(per yr)
72.0 61.0 11.0 11.5
Rate (per
million veh)
5.8 5.6 0.2 3.4
Severe &
Fatal (per yr)
2.8 4.3 -1.5 2.7
Single Veh 3.8 3.7 0.1 2.7
Example Case Study (continued):
Union Hills Drive – Phoenix, AZ
Corridor Study
Analysis
Corridor Study Analysis Overview
• Identify urban arterial roads with a large number of fixed object or single vehicle crashes
• Acquire approximately 5 years of crash data and identify cluster crash locations and/or common crashes for fixed objects
• Video tape the corridor in both directions of travel and identify characteristics where crashes occurred (also compare to locations where the crashes did not occur)
Summary of Corridor Analysis Locations
California 7 corridors (47.3 miles)
Georgia 9 corridors (23.8 miles)
Illinois 7 corridors (48.5 miles)
Oregon 8 corridors (23.7 miles)
Common Fixed Objects Involved in Cluster
Crashes along Study Corridors
• Utility Poles / Light Standards / Traffic Signals
• Trees
• Medians & Islands
• Mailbox
• Fences, Ditch or Embankment, Guardrail
• Structures
Example Corridor Analysis:
Alpharetta Highway, Fulton County, GA
Spot Map of Fixed Object Crashes
Findings based on
Corridor Analysis &
Case Studies
To-Be-Expected Observations
Crashes occurred more often at:
• Roadside ditch with non-traversable headwalls and culverts (often located at driveways)
• Uneven, hard to traverse roadside grading with various obstacles
• Locations where driver can be easily distracted by scenic views or tourist attractions
• Locations where sloping curb was used to delineate edge of road
Evaluation of Pole, Light Standard, & Post
Crashes at Urban Corridors -- Weather
Weather
Speed Limit
Total25 30 35 40 45 50 55
Dry 0 72 152 29 104 19 13 389
Wet 1 18 26 7 22 2 2 78
Ice 0 0 3 0 1 0 0 4
Fog 0 2 0 0 2 0 0 4
Snow 1 2 1 0 4 1 0 9
Other or Not
Stated
1 8 6 2 2 0 0 19
Total: 3 102 188 38 135 22 15 503
Evaluation of Pole, Light Standard, & Post
Crashes at Urban Corridors – Raised Curb
Lat.
Dist.
Speed Limit
All %
Cumul.
%25 30 35 40 45 50 55
0-1’ 0 35 71 2 19 1 1 129 28.3% 28.3%
1-2’ 2 29 44 16 50 13 3 157 34.4% 62.7%
2-4’ 0 26 27 2 30 2 3 90 19.7% 82.5%
4-6’ 1 6 23 2 18 0 0 50 11.0% 93.4%
6-8’ 0 3 10 1 9 0 0 23 5.0% 98.5%
8-10’ 0 3 1 2 0 0 0 6 1.3% 99.8%
10-15’ 0 0 0 0 0 0 1 1 0.2% 100%
15-20’ 0 0 0 0 0 0 0 0 0.0% 100%
Total: 3 102 176 25 126 16 8 456 100%
Lateral Location of Objects
Tangent Locations
• Obstacles located < 1’ up to 4’ of road edge (including within medians) hit more frequently –often by trucks
Horizontal Curve Locations (Outside of Curve)
• Obstacles located < 1’up to 6’ of road edge (including within medians) hit more frequently
Recommendation: Increase minimum lateral distance
particularly at outside of horizontal curve locations
Control Zone Design for Lateral Offset
Distance
Required Sight Distance along
Drivers' Line of Sight
Path of Drivers' Eye
Curb Face
4'
6'
4'
4'
4'
Middle Ordinate
Object Free Zone
at Inside of Curve
Std. Recommended
Object Free Zone
LEGEND
Lane Merge / Acceleration
Lane Tapers
Lane Merge / Acceleration
Lane Tapers
Lane Merge / Acceleration / Bus Bay
Lane Tapers
• Frequent crashes when object located
within 6’ of road edge at taper points
• Crashes more common at taper point even
when objects located > 6’ from road edge
but in line with lane that is ending
• Objects hit most often when within 20’
longitudinally of taper point
Recommendation: Establish buffer zone around taper
that should remain object free
Lane Merge / Acceleration / Bus Bay
Lane Tapers
4'
12'
Object Free Zone
at Taper Point
Std. Recommended
Object Free Zone
LEGEND
40'
Object
Free Zone
Object Free Zone applies to Lane Merges,
Acceleration Lanes, and Bus Bay Returns
Curb Face
4'
Intersection Issues
Crashes occurred more often at:
• Small channelization islands (frequently with sign or signal poles mounted in island)
• Pedestrian access ramps at intersection corners where ramp seems directed towards utility poles or traffic signals
• Objects located within the “curb return” boundaries
Recommendation: Establish object placement “control
zones” at intersection corners
Right-turn Lanes at Major Driveways or
Intersections
• Linear Roadside Object with
consistent placement from road
centerline (even at developing higher-
speed right-turn-lanes) causing offset
at the turn lane to be dramatically
reduced
Recommendation: Establish consistent
(minimum) object placement standards from
road edge even at turn lane locations
Landscape Buffer (Planting Strip)
Configuration
Crashes occurred more often at:
• Buffer strips 3’ wide or less with rigid objects in area
• Buffer strips 6’ wide or greater where poles are placed in line with smaller trees in center of strip or immediately adjacent to travel lanes.
Landscape Buffer (Planting Strip)
Configuration
Landscape Buffer (Planting Strip)
Configuration
Landscape Buffer (Planting Strip)
Configuration -- Continued
Recommendation:
•Avoid putting rigid objects in “landscape
buffers” 3’ wide or less.
•Place poles, light standards, or other large
objects immediately adjacent to sidewalks or on
opposite side of sidewalk -- not in center of
planting strip.
Driveway Location Object Crashes
Objects (in particular utility poles and
mailboxes) hit more often when located
at the far side of a Driveway or at
Intersections (even when located more
than 6’ from edge of road)
Recommendation:
•Where required, place objects on near side of
driveways (but away from vehicle turning radius and
in locations that do not obstruct sight distance)
Driveway Location Object Crashes
Driveway Location Object Crashes
Curb Face
4'
4'
Object Free Zone
due to Driveway
Std. Recommended
Object Free Zone
LEGEND
10 to 15' Object Free Zone
at Far side of Driveway
Drivers' Line of Sight
Drivers' Line of Sight
Concluding Remarks
• Urban Roadside Safety can be enhanced by careful treatment of known high-crash locations
• Creation of urban control zones is one promising strategy for improving urban roadside safety
• Common urban roadside crashes occur at driveways, the outside of curves, taper points, intersections, and locations where objects are positioned within 4’ to 6’ of the travel lane
Future Research Direction
• Evaluate the influence of curb as a positive guidance feature and consider low-cost solutions (edge stripes?)
• Enhance the frangible characteristics of landscape features to improve the ability to include these important components into the roadside environment
• Evaluate the influence of auxiliary lanes and how to measure the clear zone at these locations
Questions?