Transportation Engineering
School of Civil and Construction Engineering
Karen DixonKaren Dixon
Associate Professor, OSUAssociate Professor, OSU
Advisory Curve Speeds on Advisory Curve Speeds on Oregon HighwaysOregon Highways
Transportation Engineering
School of Civil and Construction Engineering
Research ObjectivesResearch Objectives• Identify the basis for the current and
proposed advisory speed posting procedures for horizontal curves and passenger vehicles
• Identify current Oregon placement strategies at a variety of locations
• Identify potential future criteria for establishing advisory speeds and determine impact
Transportation Engineering
School of Civil and Construction Engineering
Presentation OverviewPresentation Overview
• Background Information on Advisory Speeds
• Advisory Speed Candidate Posting Thresholds
• State of Practice in Oregon• Data Collection and Evaluation• Findings• Conclusions
Transportation Engineering
School of Civil and Construction Engineering
Why Do We Care?Why Do We Care?
• MUTCD recently changed recommendations
• National Committee on Uniform Traffic Control Devices has proposed additional changes for the next edition of the MUTCD
• Oregon currently has one of the most conservative policies in the U.S.
Transportation Engineering
School of Civil and Construction Engineering
Background HighlightsBackground Highlights
Common Assessment Techniques include:• Ball-bank indicator (Manual or Digital)• Computational Approach• Safe Speed Curves• Other Cited Techniques (85th-percentile,
engineering judgment, engineering study, driver perception)
Transportation Engineering
School of Civil and Construction Engineering
MUTCD Advisory SpeedsMUTCD Advisory Speeds
Current MUTCD – 16-degree for all speeds
Past Procedures for ball-bank thresholds:• 14-degrees (30 mph or less)• 12-degrees (35 to 55 mph)• 10-degrees (60 mph or more)
Or:• 10-degrees for all speeds
Transportation Engineering
School of Civil and Construction Engineering
Oregon Advisory Speed PolicyOregon Advisory Speed Policy
• 13-degrees (30 mph or less)
• 10-degrees (35 to 55 mph)
• 7-degrees (60 mph or more)
Transportation Engineering
School of Civil and Construction Engineering
Presentation OverviewPresentation Overview
• Background Information on Advisory Speeds
• Advisory Speed Candidate Posting Thresholds
• State of Practice in Oregon• Data Collection and Evaluation• Findings• Conclusions
Transportation Engineering
School of Civil and Construction Engineering
MUTCD Advisory SpeedsMUTCD Advisory Speeds
Future MUTCD Recommendation for passenger car -- ball-bank thresholds for:
• 16-degrees (30 mph or less)• 14-degrees (35 to 55 mph)• 12-degrees (60 mph or more)
These values represent 8 to 10 mph the average driver presently exceeds current posted advisory speeds
Transportation Engineering
School of Civil and Construction Engineering
Additional Recommendations Additional Recommendations by the by the National Committee on National Committee on
Uniform Traffic Control DevicesUniform Traffic Control Devices• Engineering Study based on procedures
including ball-bank criteria, accelerometer readings, or calculations using equivalent side friction values (to be modified slightly)
• Create truck advisory speed of 12-degrees
• Permit staged implementation over a period of 10 to 15 years
Transportation Engineering
School of Civil and Construction Engineering
Presentation OverviewPresentation Overview
• Background Information on Advisory Speeds
• Advisory Speed Candidate Posting Thresholds
• State of Practice in Oregon• Data Collection and Evaluation• Findings• Conclusions
Transportation Engineering
School of Civil and Construction Engineering
Survey ResultsSurvey ResultsOregon County SummaryOregon County Summary
Transportation Engineering
School of Civil and Construction Engineering
Survey ResultsSurvey ResultsRandom Sample of Oregon CitiesRandom Sample of Oregon Cities
Transportation Engineering
School of Civil and Construction Engineering
Presentation OverviewPresentation Overview
• Background Information on Advisory Speeds
• Advisory Speed Candidate Posting Thresholds
• State of Practice in Oregon• Data Collection and Evaluation• Findings• Conclusions
Transportation Engineering
School of Civil and Construction Engineering
Oregon Data Collection PlanOregon Data Collection Plan
160 Target Sites
32 Sites per each of 5 ODOT Regions
16 State Highways per Region
16 Local Highways per Region
Transportation Engineering
School of Civil and Construction Engineering
Summary of SitesSummary of SitesODOT Region
State
Site (curves)
County
Site (curves)
1 17 (19) 16 (22)
2 15 (23) 16 (30)
3 16 (23) 16 (26)
4 16 (21) 22 (30)
5 16 (18) 16 (19)
Transportation Engineering
School of Civil and Construction Engineering
Summary of Study LocationsSummary of Study Locations
• Insert map graphic here
Transportation Engineering
School of Civil and Construction Engineering
Manual Ball-Bank IndicatorManual Ball-Bank Indicator
Transportation Engineering
School of Civil and Construction Engineering
Electronic “Ball-Bank” IndicatorElectronic “Ball-Bank” Indicator
Transportation Engineering
School of Civil and Construction Engineering
Ball-Bank Indicators Mounted Ball-Bank Indicators Mounted in Vehiclein Vehicle
Transportation Engineering
School of Civil and Construction Engineering
Presentation OverviewPresentation Overview
• Background Information on Advisory Speeds
• Advisory Speed Candidate Posting Thresholds
• State of Practice in Oregon• Data Collection and Evaluation• Findings• Conclusions
Transportation Engineering
School of Civil and Construction Engineering
How Well did the Observed Sites How Well did the Observed Sites Comply with Current Oregon Comply with Current Oregon
Advisory Speed Policy?Advisory Speed Policy?
Transportation Engineering
School of Civil and Construction Engineering
Compliance DefinitionsCompliance Definitions
• “Equal To” – Posted Advisory Speeds were equal to recommended advisory speeds based on field ball-bank evaluations
• “Less than or Equal To” – Posted Advisory Speeds were equal to or less than recommended advisory speeds based on field ball-bank evaluations
Transportation Engineering
School of Civil and Construction Engineering
When is an Advisory Speed When is an Advisory Speed Plaque Needed?Plaque Needed?
• When the recommended advisory speed is more than 5 mph below the speed limit (in other words, ≥ 10 mph below the speed limit since we post in 5 mph intervals)
Transportation Engineering
School of Civil and Construction Engineering
Compliance for Speeds Compliance for Speeds Equal toEqual to Recommended Advisory Speed (All Recommended Advisory Speed (All
Curves) -- Oregon PolicyCurves) -- Oregon Policy
Based on Manual Ball-bank Readings
State – Recommended Advisory Speed (mph)
10 15 20 25 30 35 40 45 50 55 Total
Compliance Sites 0 0 3 5 10 10 17 19 21 36 121
Total Curve Directions 0 1 5 8 26 21 36 50 26 37 210
% Compliance NA 0 60 63 38 48 47 38 81 97 58%
County – Recommended Advisory Speed (mph)
10 15 20 25 30 35 40 45 50 55 Total
Compliance Sites 2 4 13 9 13 11 5 0 8 6 71
Total Curve Directions 5 13 28 32 46 41 36 18 16 11 246
% Compliance 40 31 46 28 28 27 14 0 50 55 29%
Numbers Rounded so Totals are Approximate
Transportation Engineering
School of Civil and Construction Engineering
Compliance for Speeds Compliance for Speeds Equal to or Equal to or Less ThanLess Than Recommended Advisory Recommended Advisory Speed (All Curves) -- Oregon PolicySpeed (All Curves) -- Oregon Policy
State – Recommended Advisory Speed (mph)
10 15 20 25 30 35 40 45 50 55 Total
Compliance Sites 0 0 3 7 13 12 20 23 26 37 141
Total Curve Directions 0 1 5 8 26 21 36 50 26 37 210
% Compliance NA 0 60 88 50 57 56 46 100 100 67
County – Recommended Advisory Speed (mph)
10 15 20 25 30 35 40 45 50 55 Total
Compliance Sites 2 6 13 10 16 15 16 2 15 11 106
Total Curve Directions 5 13 28 32 46 41 36 18 16 11 246
% Compliance 40 46 46 31 35 37 44 11 94 100 43
Numbers Rounded so Totals are Approximate
Transportation Engineering
School of Civil and Construction Engineering
Speed Plaque Locations Only
State: 114
County: 142
Total: 256 Curve
Directions
Plaque Posting Equal
to Recommende
d Advisory Speed
Current Speed Plaques
State Roads
54%
County Roads
38%
Speed Plaques Warranted
State Roads
42%
County Roads
32%
Transportation Engineering
School of Civil and Construction Engineering
How Well did the Observed How Well did the Observed Sites Comply with Current and Sites Comply with Current and
Proposed MUTCD Advisory Proposed MUTCD Advisory Speed Recommendations?Speed Recommendations?
Transportation Engineering
School of Civil and Construction Engineering
All Study Locations (with or without Speed
Plaques)
State: 210
County: 246
Total: 456 Curve Directions
Advisory Speed
Indications Comply with
(Equal To) Recommende
d Advisory Speeds
State Roads
Oregon
13-10-7
58%
MUTCD
16-degree
53%
Future
16-14-12
57%
County Roads
Oregon
13-10-7
29%
MUTCD
16-degree
38%
Future
16-14-12
38%
Transportation Engineering
School of Civil and Construction Engineering
Oregon Ball-bank Manual vs Digital Advisory Speeds
Transportation Engineering
School of Civil and Construction Engineering
Presentation OverviewPresentation Overview
• Background Information on Advisory Speeds
• Advisory Speed Candidate Posting Thresholds
• State of Practice in Oregon• Data Collection and Evaluation• Findings• Conclusions
Transportation Engineering
School of Civil and Construction Engineering
Summary of FindingsSummary of Findings
• Current Oregon Policy compliance varies, but advisory speeds of 30 to 45 mph consistently have a lower compliance
• Compliance defined as Equal to Recommended Advisory Speed much more rigid than a definition of Equal to or Less than
Transportation Engineering
School of Civil and Construction Engineering
Summary of FindingsSummary of Findings
• Future 16-14-12 threshold at Advisory Plaque Sites okay for 35% of the sites (with 80% equal to or less than this less conservative criteria)
• Future 16-14-12 threshold at All Study Sites okay for 29% to 38% of the sites (using “Equal To” threshold)
Transportation Engineering
School of Civil and Construction Engineering
Questions?Questions?