urban roadside safety -- is there anything we can do to improve safety performance?

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?