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Low Cost Safety Improvements Pooled Fund Steering Committee Meeting Notes, 3/8/05
The following are the March 8th, 2005 meeting notes as distributed to the Low Cost Safety Improvements Pooled Fund Steering Committee:
Low Cost Safety Improvements Pooled Funds Study
Steering Committee Meeting Agenda
Tuesday, March 8th, 2005
Turner Fairbanks Highway Research Center
7:30- 8:00 |
Breakfast |
| 8:00 - 8:30 |
Welcome, Introduction, and Overview of Steering Committee Activities, Kerry Perrillo and Michael Trentacoste |
8:30 - 9:00 |
Overview of Preliminary Survey Findings, Kim Eccles |
9:00 - 9:30 |
Presentation on Study Designs, Dr. Bhagwant Persaud |
|
Meeting attendees will be divided into two groups to discuss each of the potential strategies, share their experiences, and assess the feasibility of evaluating each strategy. Each group will be asked to identify those strategies which should not be considered for the study.
|
9:30 - 10:30 |
Breakout Sessions
Group A: Lane Departure (led by Dr. Hugh McGee)
Group B: Unsignalized Intersections and Aggressive Driving (led by Kim Eccles) |
10:30 - 10:45 |
Break |
10:45 - 11:45 |
Breakout Sessions
Group A: Unsignalized Intersections and Aggressive Driving (led by Kim Eccles)
Group B: Lane Departure (led by Dr. Hugh McGee) |
11:45- 12:00 |
Reconvene and Summary of Morning |
12:00 -1:00 |
Lunch |
1:00 - 1:15 |
Explanation of Balloting Procedures |
1:15 - 2:30 |
Open Balloting |
2:30 - 3:00 |
Summary of Ballots and Discussion of Results |
3:00 - 3:15 |
Break |
3:15 - 4:30 |
Discussion of Anticipated Implementation of Strategies |
4:30 - 5:00 |
Next Steps |
5:00 |
Meeting Adjournment |
Introduction, and Overview of Steering Committee Activities
-
Mike Trentacoste (FHWA) welcomed the group and discussed housekeeping items
-
Kerry Perrillo (FHWA) gave an overview of AASHTO participation and an evolution of the study. She gave an explanation of the strategies eliminated and the high cost strategies included.
Overview of Preliminary Survey Findings
-
Kim Eccles (BMI-SG) welcomed the group, and gave an overview of the survey project and the survey findings. She explained that the strategies that were redundant or proven were removed.
-
A discussion followed on strategies to add and remove for all three strategy categories
-
Tom Welch asked how to share information with states that are not present at this meeting. Kerry Perrillo answered that notes will be posted on Pooled Funds Study website.
-
It was noted that state by state research does not contribute well to the overall research pool. Effectiveness of strategies may vary by state and demographics.
- Michael Trentacoste gave an invitation for suggestions of further research.
Overview of Study Design
-
Dr. Bhagwant Persaud (BMI-SG Consultant) discussed the basis of study design and evaluation. He explained experimental vs. observational studies.
-
The question was raised regarding the problem of regression to the mean. It was noted that regression to the mean can
cause a significant overestimation of the results of a treatment. Examples of treatments that raise traffic
volumes are addition of left turn lanes and adding roundabouts. Normalizing doesn't work because the relationship
between crashes and traffic volumes is a non-linear relationship.
-
A handout was distributed- How Many Treatment Sites are required? -Attachment 2
Breakout Sessions
-
Meeting attendees were divided into two groups, lane departure and aggressive driving
strategies, and unsignalized intersection strategies. A presentation of each strategy was given and participants were
asked to share their experiences, assess the feasibility of evaluating each strategy, and identify which of any strategies should be removed. The following questions and comments were
inspired by the presentations.
Breakout Session 1
Group A: Lane Departure and Aggressive Driving (led by Dr. Hugh McGee)
-
LD1: Profiled thermoplastic strips for centerlines
-
Brian Stanford (TX) - Inverted profiled thermoplastic strips for centerlines gives retroreflectivity, raised and inverted gives rumble effect. Treatment needs to take into consideration the amount of traffic. Application also influenced by snow plow usage.
-
Robert Hull (UT) - Should strategies that are not applicable across the board be removed? I.e. northern states cannot use certain rumble strips (because of snow plows).
-
Gary Modi
(PA) - Consider what is best for your state.
-
Michael Trentacoste - Be objective as far as overall use of strategy, but most will lean toward what is applicable within their state.
-
Loren Hill - Minnesota interested in study of this strategy and the possibility of its modification to suit the needs of each state. Would like wet reflectivity
without snow plow prohibition.
-
Harry Taylor (FHWA) - Vote on those that you
would like to implement within your state.
-
LD2: Wider cross sections on 2-lane roads
-
Cass Napier (KY) - Wider cross-sections have decreased crashes, but increased severity of crashes in KY.
-
Gary Modi - Study influence of different variations of cross-section widening (with or without shoulder widening for example).
-
John Carey (CT) - Is the experimental design going to account for crash reduction outside of the normal scope (non-fatal accidents, a-type, k-type, fatalities, driveway crash reduction).
-
Cass Napier - Agree that type of crash is important in evaluation.
-
Faria Emanain (OK) - Concern about cost and maintenance as a part of the evaluation, creates resistance to implementation.
-
Mike Griffith (FHWA )- Use of cable guardrails in European countries to aid with alternating passing lanes.
-
Mike Trentacoste - Germany uses pavement markings for alternate passing lanes. Also, signage which gives detail of passing lane availability.
-
LD6: Median Barriers
-
Cass Napier - Concerns about redundancy of rumble strip studies.
-
Gary Modi - Center-line rumble strips may cause motorcycle issues.
-
How did center-lane rumble strips get a fair rating for suitability for crash based evaluation? Answer: Possibility of evaluation, pending volunteering states for trials.
-
Gary Modi - Looking into safety of raised, snow plowable pavement markings due to the markers being thrown from the roadway and at vehicles.
-
Gary Modi - Tracking of skid resistant pavement. State trying to implement a policy. No reliable data on skid numbers; variability based on different ways to measure this data. Tires and other variables make research difficult.
-
LD11: Enhanced Shoulder or in-lane delineation and marking for sharp curves
-
LD12: Delineate poles or trees with reflective tape
-
Gary Modi - Notes that this treatment only works when you have control of the vehicle. The ultimate treatment would be to remove the item.
-
Mike Griffith - Does marking of trees and other objects pull people further off the roadway in low-light areas? Do individuals track on these markings?
-
Roundtable discussion, Gary Modi, Harry Taylor, Loren Hill, etc - consensus, this is a situational strategy that may not be effective when objects are located too far off the roadway.
-
LD13: Enhanced Guardrail Delineation
-
Brian Stanford - Standard treatment in TX to help.
-
Gari Modi - PA uses this in some situations.
-
Faria Emamian - Suggests that this reflectivity reduces wear and denting on guardrails. This reduces maintenance costs.
-
Gary Modi - This increased delineation can increase traffic speeds because of increased driver
comfort.
-
Harry Taylor - Post delineation may help. Reduce redundancy of post delineation and guardrail reflectivity.
-
LD14: Truck Pullovers
-
LD15: Automated Warning Signs for Curves
-
Cass Napier - Cost effectiveness of keep up.
-
John Carey - Issues with teens using this to see how fast they can make it thru a curve and then bragging about speeds on internet.
-
Gary Modi -
Implementation resulted in high cost and lots of maintenance issues.
-
A1/A2: Target enforcement for aggressive driving
-
A5: Reduce nonrecurring delays and provide better information about these delays
Robert Hull - Salt Lake is broadcasting travel times to certain points via changeable message signs.
David Piper (IL) - His state is using limitations on time spent in freeway left lanes (3/4 mile).
Brian Stanford - Texas no longer allowed to post "slower vehicles keep right sign," must post "left lane for passing only."
Loren Hill - Use of aerial video to profile aggressive drivers and aid in their apprehension/conviction.
Concern about variability in specificity of discussed strategies.
Group B: Unsignalized Intersections (led by Kim Eccles)
Note taker did not
note who made the comments
-
U1: Driveway closures/relocations
-
35% crash data
-
Larger study- is it enough data to use
-
Allowing left turn to just have right-in, right-out; not enough data for analyzing driveway crashes
-
Case by case basis to analyze driveway closures
-
U2: Driveway turn restrictions
-
U3: Longer left turn lanes at intersections
-
Why is it poor? Part of our implementation, have huge safety projects
-
In VA, moderate costs is underestimating it because of road realignment
-
U4: Offset left-turn at intersections
-
Comment - problem with pedestrian walks
-
City of Minneapolis has this, but has limited left turn on but not left turn offset
-
U5: Bypass lanes on shoulders at T-intersections
-
Tested in
Minnesota
-
Found effective in low volume, rural in S.
Dakota
-
Use shoulder,
reinforcing shoulders
-
Kansas
-
U6: Left turn acceleration lanes at divided hwy
intersections
-
U7: Longer right-turn lanes at intersections
-
See crashes - see
severe crashes
-
In Arizona,
Minnesota, Wisconsin,
-
U8: Offset right turn lanes at intersections
-
U11: Restrict or eliminate turning maneuvers by signing
-
U12: Restrict or eliminate turning maneuvers by
providing channelization or closing median openings
-
U13: Convert four legged intersections to two T-intersections
-
Offset should be
left to right
-
The picture in
the presentation shows left to right, but it should be right to left because it
is safer than left to right
-
NY - how many
states are now converting to roundabouts?
-
Change in volume
-
U15: Indirect left turn treatments to minimize
conflicts at divided hwy. intersections
-
U23: Flashing beacons at stop controlled intersections
-
U25: Lane assignment signing or marking
-
U31: Splitter islands
-
Questions/comments from participants:
-
Look at the
severity of right turn lane and unsignalized intersection
-
Hope we are look at severity/reduce the overall severity of crash
-
Currently analyzing 4 to 3 lanes conversion, just striping a 4 lane to 3 lane
Intersection Lighting was added to the ballot
Breakout Session 2
Group A: Lane Departure and Aggressive Driving (led by Dr. Hugh McGee)
-
LD3: 2-way center left turn lane
-
Sweden - Increase in head on crashes.
-
Patrick Brady -
2-way center left turn lane increases crashes as traffic volumes increase and
approach certain levels (exact volumes to be determined).
-
Found to be
effective to certain volumes.
-
LD5: Alternating passing lanes or four-lane sections at key locations to prevent head-on crashes
-
Pierre Jomini (MT) - creating passing sections on 2-lane roads. Separate, just for the purpose of passing.
-
LD6: Median
Barriers for Narrow-Width Medians on Multilane Roads
-
Patrick Brady -
clarification of multilane roads meaning 4-lane.
-
Patrick Brady -
Uses of Quick Curb.
-
LD7: Install edgeline "profile marking,"
edgeline rumble strips or modified shoulder rumble strips on section with
narrow or no paved shoulders
-
Bhagwant Persaud
- Believes this strategy to be evaluated by NCHRP 17-25.
-
Thomas Welch -
mention of variations on this strategy.
-
Patrick Brady -
Further thoughts on more aggressive rumble strips.
-
Harry Taylor -
Some may be snow plowable.
-
LD8: Midlane Rumble Strips
-
Patrick Brady -
Never heard of this.
-
Shawn Troy (NC) -
NC did a quick comparison. Showed no
change in crashes. Many variations in
offset distances of shoulder rumble strips.
NC has discussed midlane rumble strips, but never tested it.
-
Patrick Brady -
It would be nice to see someone experiment with this, but it would likely make
motorcyclists cringe.
-
LD9: Provide Enhanced Pavement Markings
-
Thomas Welch -
Missouri, problem with these markers being thrown by snowplows into drivers'
windshields.
-
Patrick Brady -
We need to know if it is going to make things worse. Concern about increased speeds and crashes.
-
Bhagwant Persaud
- Was a part of NCHRP study on a similar concept. Hugh questions if this study includes enough crash data to reach
a conclusion. At this time we can not
draw a conclusion from the study as to whether crashes increase because of
increased speed
-
Patrick Brady -
Increased speed versus increased visibility; usefulness of markings in gauging
speed and recognition of curves.
-
Shawn Troy -
Concern about the study of crash numbers, severity, and speed as factors in
determining the situational use of this strategy.
-
LD10: Skid
Resistant Pavement Surfaces
-
Barbara O'Rourke
(NY) - NY has a lot of data on this.
-
Bhagwant Persaud
- NY has had successful applications of this in intersections.
-
Patrick Brady -
FL has skid data as well.
-
Maryland also has
some data. Look at Colesville Rd. in
Silver Spring.
-
LD11: Enhanced shoulder or in-lane delineation and
marking for sharp curves
-
Clifford Reuer
(SD) - Would this be used in addition to other, roadside delineation?
-
Patrick Brady -
Would this be in addition to advance warning signs, chevrons, etc.
-
Pierre Jomini -
Would an advised speed be better than slow?
Slow for one person may be different for another.
-
A good contact
for this strategy in Florida, Mendocino County, Gibb Peasley, University of
Florida.
-
LD12: Delineate utility poles or trees with reflective
tape
-
Patrick Brady -
Targeting instead of delineation. Is
this going to be positive or negative delineation?
-
Clifford Reuer -
Concern about uniformity.
-
Group - Utility
companies may limit nailing / bolting into utility poles.
-
LD13: Enhanced guardrail reflectors
-
Patrick Brady -
most reported accidents in FL are no-injury crashes.
-
LD14: Pavement Pull-offs for drowsy truck drivers on
isolated segments
-
Shawn Troy - NC
implementing this for safe pull-offs for truck drivers, emergency etc. NC putting this in Gorge sections.
-
Patrick Brady -
FL implementing this with emergency pull-offs in work zones. Also, putting in truck rest areas with
showers that allow drivers to sleep in cabs.
-
Neil Boudreau
(Ma) - Check with Utah. They have a
plan to deal with drowsy drivers.
-
LD15: Automated warning signs when driving too fast for
curve
-
Patrick Brady -
Use of a similar system with accelerating in-pavement lights.
-
Tennessee, using
this for trucks.
-
Group - This
system used primarily for truckers, some includes weigh on the go technology
GA, TN, VA. Concern about rollover
data.
-
Patrick Brady -
once off roadway, rollover is a result of slope.
-
Harry Taylor -
Causation studies are very difficult because of the methodology of police
reporting.
-
Group - Causes
for leaving the roadway drowsy, drunk, speeding, distraction, deer, offensive
drivers.
-
A1/A2: Target Enforcement for Aggressive Driving
-
Clifford Reuer - Has seen significant reduction during enforcement, reverses when enforcement stops. This tends to be a temporary fix.
-
Barbara O'Rourke - Enforcement data is generally from the enforcement period only. Seems inaccurate.
-
Use of video imaging helps to establish effect and improve enforcement.
-
Patrick Brady - Random enforcement during enforcement campaign can affect driver behavior patterns by getting they used to police present.
-
Bhagwant Persaud - Crash data may go up because more crashes will be reported.
-
Tom Welch - Effectiveness is limited by volume and police availability.
-
Patrick Brady - Saturation of law enforcement happens in this type of enforcement.
-
Shawn Troy - May reduce percentage of speeders as opposed to significant reduction in average speeds.
-
Barbara O'Rourke - Evaluation of these strategies, data available.
-
A3: Educate and impose sanctions against repeat offenders
-
A4: Change or mitigate the effects of identified elements in the environment
Group B: Unsignalized Intersections (led by Kim Eccles)
Note taker did not note who made the comments
-
U2: Driveway/turn restriction
-
U3: Longer left turn lanes at intersections
-
U4: Offset left turn lanes at intersections
-
U5: Bypass lanes on shoulders at T-intersections
- Decrease in safety
- FL - doing 4 legged intersections
- Hundreds of installations
- 20 t intersection
- Didn't do a before and after study, did a compare this intersection with this intersection
-
U6: Left turn acceleration lanes at divided hwy intersection
- Jan Hanson - contact to gather more data - information came from Loren Hill
-
U7: Longer right-turn lanes at intersections
- If you use shoulder (existing) as a right turn lane
- Make a distinction in right turn lane
- FHWA - study
evaluation
- Mike Griffith - asked how we are defining the term longer
-
U8: Offset right turn lanes at intersections
- Montana - had problem with because of crashes occurring with right turn and incoming traffic
-
U11: Restrict or eliminate turning maneuvers by signing
- At the intersection
- Effective with physical barriers
-
U13: Convert four legged intersections to two T-intersections
- Picture is transposed
- Safer - right turn left turn
- NCHRP 17-25
- Look at FHWA - comparison/accident studies on four-legged and T-intersection
-
U18: Roadside markers or pavement markings for gap assistance
- Roadside markers or pavement markings for gap assistance
- Gary Ogletree tried. Does the person at the stop sign read the signs?
- Few numbers/little impact of roadside marker or pavement marking because people do not read the sign
- Can examine through human factors
- More of a daytime hours strategy
-
U20: Rumble strips on intersection approaches
- Removed because Janet is studying this topic
-
U22: Pavement markings with supplementary messages, such as "stop ahead"
-
U23: Flashing beacons at stop controlled intersections
- For 2/4 way stop
- Loren Hill said did not use 2 way stop
- No study on 2 way stop
-
U29: Targeted public information and education on safety problems at specific intersections
- Area wide campaign
- Hard asset safety on area wide campaign
-
U30: Enhanced signing and delineation
-
U31: Splitter islands on the minor-road approach to an intersection
- Loren Hill mentioned the video, Joe Bared's work on speeds and unsignalized intersections. Developed a video and distributed to some
states—new strategies to use novel techniques to reduce speeds—none of the
strategies are on the ballot today except U31, splitter island, is on the
videotape, and there are rumble strips on the main line
-
U34: Improved maintenance of stop signs
- Peter Kissinger (AAA) -Looking at higher grade reflective material on strategy 34
- Tim gates (TTI) - looked at stop signs with increased retro and couldn't find a crash
effect. He also looked at retro strips too. Kim Eccles did study of fluorescent yellow -not crashed based, but saw small increases in some with
increased retro
- John Carey used throughout the state so has a large sample size. Group would like to see retro added to the ballot
Balloting and Afternoon Session
-
A revised ballot was distributed based on changes made
in the morning session
-
Some strategies
revised, some strategies were deleted because they were already under study,
also based on breakout sessions, some strategies were added, and some were
combined
-
Discussion of strategies involving left and right turn
lane
-
Mike Griffith
gave a brief overview of a cost evaluation study for safety effectiveness of
intersection left and right turn lanes
-
Tom Welch noted
he had an interest in severity for this study instead of a simple quantitative
analysis
-
Bhagwant Persaud
promised to always include severity in analysis of this strategy
-
Mike Griffith
noted the decision to keep this strategy in the ballot is based on limitations
of original study
-
Kim Eccles noted
that (U7- Longer right-turn lanes at intersections) will be modified to include
severity as a condition of evaluation of existing lanes
-
Discussion of partial lighting of unsignalized rural
intersections
-
Cass Napier has
in interest in the provision of partial lighting of unsignalized rural
intersections
-
Patrick Brady feels that this is really the issue of the effects of different light
intensities on various intersection usages and types
-
Discussion of addition of cable barriers to LD5
-
Patrick Brady was concerned about the addition of a cable barrier (LD16) for alternating passing lanes or four-lane sections at key locations to prevent HO crashes (LD5)
-
Hugh McGee stated it would be used as an alternative passing lane strategy
-
Mike Trentacoste clarified that the cable is in place on a very small median
-
Harry Taylor explained the reality vs. the perception of deflection of cable medians in a crash situation. They do not present as much as a problem as some would believe.
-
John Nagle (IN) requested review of the midlane rumble strip strategy.
-
Kerry Perrillo stated that she will continue to track studies to eliminate those that are already being studies and which are in the top 20 balloting
-
Kim Eccles explained the balloting procedure, the open balloting process took place, and the results were reported (see Attachment 2)
Implementation Discussion
Wrap-Up
-
Kerry Perrillo
led a wrap-up discussion
-
A1 was ranked
highly; Kerry said she will mention it to NCHRP when they meet on behavioral
study. A1 was modified top include
educating judges and litigators.
-
Kerry thanked
meeting attendees for their eager participation
- Kerry noted that
there will be a technical advisory committee (TAC) meeting about once a
year. The money taken from the Pooled
Fund Study was discussed. 23 States
joined, 2.43 million from states, money from FHWA, 3.93 million total. Possibility of additional NCHRP funding
equating to a total of 4.6 million.
Hoped that 20 strategies can be studied with funds. BMI-SG will follow up and begin evaluations
and experimental design. Project will
be contracted out at some point this summer.
- Tom Welch asked
if it will be contracted out to one or multiple contractors
-
Kerry answered
preferably one contractor with (possibility of) subcontractors
-
Tom Welch noted
there may be benefits to using several firms to evaluate data from various
states
-
Patrick Brady
voiced concerns over how to collect the data.
States don't have the man power.
One contractor would be preferable for this purpose because it is easier
to deal with fewer individuals.
-
Mike Trentacoste
insured that regardless of one or more contractors, assembling a team to
perform tasks.
-
The group offered
options on how to go about selecting a contractor/ assembling a team to perform
these tasks.
-
It was mentioned
that there is a website www.pooledfund.org. Click under proposed studies
TPF-5(099). Will update information and
will include meeting notes. Eventually
there will be an exclusive website for this project.
- Patrick Brady
suggested that the contractor may be best to setup and maintain website for
project.
-
Kim Eccles stated
she will follow up on implementation.
She invited states to e-mail her regarding any new developments with
states represented or not represented here.
Meeting adjourned
Attachment 1: Balloting Results
Strategy ID |
Strategy |
Score |
Ballots |
LD7 |
Install edgeline "profile marking," edgeline rumble strips or modified shoulder rumble strips on section with narrow or no paved shoulders |
138 |
18 |
LD11 |
Enhanced shoulder or in-lane delineation and marking for sharp curves |
119 |
16 |
LD9 |
Provide enhanced pavement markings |
67 |
12 |
LD5 |
Alternating passing lanes or four-lane sections at key
locations to prevent HO crashes |
61 |
10 |
U23 |
Flashing beacons at stop controlled intersections |
60 |
9 |
LD3 |
Center two-way left-turn lanes for four- and two-lane
roads |
54 |
9 |
LD6 |
Median barriers for narrow-width medians on multilane
roads to prevent HO crashes |
54 |
9 |
U5 |
Bypass lanes on shoulders at T-intersections |
51 |
10 |
LD17 |
New: Combination of lane width versus shoulders |
48 |
7 |
U22 |
Pavement markings with supplementary messages, such as
"stop ahead" |
47 |
8 |
LD1 |
Install profiled thermoplastic strips for centerlines |
44 |
7 |
LD4 |
Narrow "buffer median" on two-lane roadways |
39 |
6 |
U18 |
Roadside markers or pavement markings for gap assistance |
34 |
8 |
A1 |
Revised: Target (manual) enforcement for aggressive
driving combined with educational and public information |
34 |
8 |
U4 |
Offset left-turn lanes at intersections |
33 |
8 |
U35 |
New: Stops signs with increased retroreflectivity |
32 |
6 |
LD15 |
Automated warning signs when driver too fast for
curve (particularly for trucks) |
31 |
6 |
U6 |
Left turn acceleration lanes at divided highway
intersections |
28 |
5 |
U36 |
New: Intersection lighting intensity |
28 |
7 |
U7 |
Longer right-turn lanes at intersections |
24 |
3 |
LD2 |
Wider cross sections on two-lane roads |
24 |
5 |
U15 |
Indirect left-turn treatments to minimize conflicts at divided highway intersections |
23 |
3 |
U37 |
New: Use shoulder for right turn lane (variation of U7) |
21 |
3 |
U25 |
Lane assignment signing or marking at complex intersections |
21 |
5 |
LD13 |
Enhanced guardrail reflectors |
18 |
3 |
A2 |
Revised: Target (automated) enforcement for aggressive
driving combined with educational and public information |
18 |
4 |
LD8 |
Midlane rumble strips |
17 |
3 |
U8 |
Offset right turn lanes at intersections |
17 |
3 |
U17 |
Change horizontal and/or vertical alignment of approaches |
17 |
3 |
U12 |
Channelize or close median openings |
14 |
2 |
U19 |
Large regulatory and warning signs at intersections |
13 |
4 |
U30 |
Enhanced signing and delineation |
12 |
4 |
A7 |
Widen painted edgelines to slow and calm aggressive drivers |
8 |
2 |
U31 |
Splitter islands on the minor-road approach to an intersection |
7 |
1 |
LD10 |
Provide skid-resistant pavement surfaces |
7 |
2 |
LD14 |
Widened pavement/pull-offs on isolated segments for emergency situations |
6 |
1 |
U33 |
Dashed markings (extended left edgelines) for major-road continuity across the median opening at divided highway intersections |
6 |
1 |
U1 |
Driveway closures/relocations |
6 |
2 |
A5 |
Reduce nonrecurring delays and provide better information about these delays |
6 |
2 |
U9 |
Right turn acceleration lanes at intersections |
6 |
3 |
LD16 |
New: Adding cable barrier for LD5 |
5 |
2 |
U14 |
Convert offset T-intersections to four legged intersections |
5 |
2 |
A4 |
Change or mitigate the effects of identified elements in the environment |
5 |
2 |
A3 |
Education and sanctions against repeat offenders |
4 |
1 |
U24 |
Retime adjacent signals to create gaps at stop-controlled intersections |
3 |
1 |
U3 |
Longer left turn lanes at intersections |
2 |
1 |
U2 |
Driveway turn restrictions |
1 |
1 |
U10 |
Full width paved shoulders in intersection areas |
1 |
1 |
A6 |
"Slower Vehicles Keep Right" signs |
1 |
1 |
LD12 |
Delineate utility poles or trees with retroreflective tape |
0 |
0 |
U11 |
Restrict or eliminate turning maneuvers by signing |
0 |
0 |
U13 |
Convert four legged intersections to two T-intersections |
0 |
0 |
U16 |
Close or relocate "high-risk" intersections |
0 |
0 |
U20 |
REMOVED |
0 |
0 |
U21 |
Supplementary stop signs mounted over the roadway |
0 |
0 |
U26 |
Turn path markings |
0 |
0 |
U27 |
Double yellow centerline on the median opening of a divided highway at intersections |
0 |
0 |
U28 |
Targeted enforcement to reduce stop sign violations |
0 |
0 |
U29 |
Targeted public information and education on safety problems at specific intersections |
0 |
0 |
U32 |
Stop bar (or provide a wider stop bar) on minor road approaches |
0 |
0 |
U34 |
Improved maintenance of stop signs |
0 |
0 |
Attachment 2: Bhagwant Persaud's handout
How many treatment sites are required?
Basics
- When planning a before-after safety evaluation study it is vital to ensure that enough data are included such that the expected change in safety can be statistically detected.
- In the planning stage the expected change in safety is not known, but it is still possible to make a rough determination of how many treatment sites are required based on the best available information about
- the expected change in safety
- the average number of crashes per site
- From this, one could estimate, for the number of available sites, the change in safety that can be statistically detected.
- Available sample size estimation methods are (conservatively) based a conventional before-after study with comparison group design
- Statistical
accuracy attainable for a given sample size is described by the standard
deviations of the estimated percent change in safety.
- One
can estimate P-values for various sample sizes and expected change in
safety for a given crash history.
- A
P-value of 0.10 roughly translates into 90% confidence and is generally
regarded as a limiting value.
- Assume that the number of comparison sites is equal to the number of treatment sites.
- Assume (from published data)
- 20 crashes/site-year of which
- 3.5 are right angle crashes and
- 12.0 are rear-end crashes
- Assume three years of 'before' crash counts, one and a half years of 'after' period crash counts.
P-values for various sample sizes and expected changes in safety
(based on equal number of comparison sites)
Number of treated sites |
20 |
60 |
?? |
% change in crashes |
10% |
20% |
30% |
10% |
20% |
30% |
10% |
20% |
30% |
Right angle crashes |
0.58 |
0.23 |
0.05 |
0.42 |
0.08 |
<0.01 |
0.33 |
0.05 |
<0.01 |
Rear-end crashes |
0.51 |
0.23 |
0.10 |
0.42 |
0.14 |
0.04 |
0.40 |
0.12 |
0.03 |
(Shaded
cells indicate where P-values of  0.10 are attainable)
-
Example 1: If the sample
contains 20 treated sites, and a 30% reduction in the number of right angle
crashes is expected due to RLC installation, we may expect to obtain a
statistically significant result at the 10% level (since P actually equals
0.05).
-
Example 2: With 60
treated sites, if there is a 20% increase in the number of rear-end crashes, we
do not expect a statistically
significant result at the 10% level (since P > 0.10). However, that result
would be significant at the 15% level.
-
Assessment of available treatment site samples:
Best judgment on possibility of detecting safety effects at the P = 10%
level
(Assuming a 25%
decrease in right angle crashes and a 30% increase in rear end crashes)
Crash Type |
City 1 |
City 2 |
City 3 |
City 4 |
All |
Right angle |
Y |
Y |
Y |
|
Y |
Injury right angle |
Y |
|
Y |
|
Y |
Rear end |
Y |
Y |
Y |
|
Y |
Injury rear end |
Y |
|
Y |
|
Y |
(Y significant results may be obtained, significant
results may not be obtained)
Case study 2: Centre line rumble strips
Minimum required 'before' period mile-years
for treated sites
for detecting an expected change in safety (P 0.10)
(assumes equal length of before and after periods)
Expected Percent Reduction in Crashes |
Equal number of mile-years for treatment and comparison sites |
Half as many mile-years for comparison as for treatment sites
(Pop Quiz!) |
2.10 crashes
/mile/year |
0.54 crashes
/mile/year |
2.10 crashes
/mile/year |
0.54 crashes /mile/year |
40 |
13 |
52 |
|
|
20 |
87 |
339 |
|
|
10 |
426 |
1659 |
|
|
|
