Transportation Engineering School of Civil and Construction Engineering Karen Dixon Associate Professor, OSU Advisory Curve Speeds on Oregon Highways.

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



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



Presentation OverviewPresentation Overview

• Background Information on Advisory Speeds

• Advisory Speed Candidate Posting Thresholds

• State of Practice in Oregon• Data Collection and Evaluation• Findings• Conclusions



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.



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)



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



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)









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



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









Survey ResultsSurvey ResultsOregon County SummaryOregon County Summary



Survey ResultsSurvey ResultsRandom Sample of Oregon CitiesRandom Sample of Oregon Cities









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



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)



Summary of Study LocationsSummary of Study Locations

• Insert map graphic here



Manual Ball-Bank IndicatorManual Ball-Bank Indicator



Electronic “Ball-Bank” IndicatorElectronic “Ball-Bank” Indicator



Ball-Bank Indicators Mounted Ball-Bank Indicators Mounted in Vehiclein Vehicle









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?



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



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)



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 40 31 46 28 28 27 14 0 50 55 29%

Numbers Rounded so Totals are Approximate



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 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 40 46 46 31 35 37 44 11 94 100 43

Numbers Rounded so Totals are Approximate



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%



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?



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%



Oregon Ball-bank Manual vs Digital Advisory Speeds









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



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)



Questions?Questions?

Transportation Engineering School of Civil and Construction Engineering Karen Dixon Associate Professor, OSU Advisory Curve Speeds on Oregon Highways.

Documents

engineering judgment

oregon highways slide

vehicle slide

impact slide

truck advisory speed

mutcd oregon

driver perception slide

osu advisory curve speeds