Curve Advisory Speed Existing Practices and New Procedures OR

CURVE ADVISORY SPEED WORKSHOP Introduction Workshop Instructor –Robert Milstead, PE, PTOE (Brudis & Associates, Inc.) Workshop Objectives –New criteria and tools MUTCD 2009 compliance New procedures –Limitations of current practices –Uniform and consistent advisory speeds –Horizontal alignment warning signs –Participant discussion and feedback

CURVE ADVISORY SPEED WORKSHOP Agenda Background MUTCD 2009 Criteria and Guidelines Current Practices to Determine Advisory Speed New Procedures to Determine Advisory Speed Support: Curve Advisory Speed Worksheet Confirm Advisory Speed and Curve Sign Selection Step by Step Procedures Exercises Summary

CURVE ADVISORY SPEED WORKSHOP Background What is an Advisory Speed –Definition (MUTCD 2009 ): a recommended speed for all vehicles operating on a section of highway and based on the highway design, operating characteristics, and conditions. –Uniform and consistent advisory speed together with other horizontal alignment warning signs conveys a realistic message establishing driver expectancy and promoting effective roadway operations. –Typical applications: horizontal curves, highway ramps, and work zones.

CURVE ADVISORY SPEED WORKSHOP Background Importance of Uniform and Consistent Advisory Speeds –Safety –Positive Guidance –Driver Respect for Signs

CURVE ADVISORY SPEED WORKSHOP Background Crash Statistics (2008) – 52% of all fatal crashes involve roadway departures. –9,475 (28%) fatal crashes occurred on a curve. – 85% of the fatal curve crashes involve roadway departures. “A roadway departure crash is defined as a non-intersection crash which occurs after a vehicle crosses an edge line or a center line, or otherwise leaves the traveled way.” Source: NHTSA FARS 2008 & FHWA Safety Program

CURVE ADVISORY SPEED WORKSHOP Background A Nationwide Survey of 344 Practitioners (Lyles and Taylor, 2006) –Uniformity among curves 45% believe that advisory speeds are not uniform throughout their own states. Only 58% believe that advisory speeds are consistently estimated. –Consistency with driver expectation 62% believe that advisory speeds are too low. 3% believe that advisory speeds are too high.

CURVE ADVISORY SPEED WORKSHOP Background Current Advisory Speeds –Lack of uniformity among curves –Commonly more conservative than guidance Ball-bank Based (Uniformly Re-established) vs. Posted Advisory Speeds at 65 Curves.

CURVE ADVISORY SPEED WORKSHOP Background Current Advisory Speeds –Inconsistent with Driver Expectation –Majority of drivers exceed advisory speed by 10 mph Average and 85 th % Speeds vs. Posted Advisory Speeds (data from 65 curves)

CURVE ADVISORY SPEED WORKSHOP MUTCD 2009 Section 1A.04 Placement and Operation of Traffic Control Devices Guidance: Placement of a traffic control device should be within the road user’s view so that adequate visibility is provided. To aid in conveying the proper meaning, the traffic control device should be appropriately positioned with respect to the location, object, or situation to which it applies. The location and legibility of the traffic control device should be such that a road user has adequate time to make the proper response in both day and night conditions. Traffic control devices should be placed and operated in a uniform and consistent manner. Unnecessary traffic control devices should be removed. The fact that a device is in good physical condition should not be a basis for deferring needed removal or change. Source: FHWA MUTCD 2009

CURVE ADVISORY SPEED WORKSHOP MUTCD 2009 Section 2C.02 Application of Warning Signs Standard: The use of warning signs shall be based on an engineering study or on engineering judgment. Guidance: The use of warning signs should be kept to a minimum as the unnecessary use of warning signs tends to breed disrespect for all signs. In situations where the condition or activity is seasonal or temporary, the warning sign should be removed or covered when the condition or activity does not exist. Source: FHWA MUTCD 2009

CURVE ADVISORY SPEED WORKSHOP MUTCD 2009 Section 2C.08 Advisory Speed Plaque (W13-1P) Option: The Advisory Speed (W13-1P) plaque (see Figure 2C-1) may be used to supplement any warning sign to indicate the advisory speed for a condition. Standard: The use of the Advisory Speed plaque for horizontal curves shall be in accordance with the information shown in Table 2C-5. The Advisory Speed plaque shall also be used where an engineering study indicates a need to advise road users of the advisory speed for other roadway conditions. Source: FHWA MUTCD 2009 If used, the Advisory Speed plaque shall carry the message XX MPH. The speed displayed shall be a multiple of 5 mph. Except in emergencies or when the condition is temporary, an Advisory Speed plaque shall not be installed until the advisory speed has been determined by an engineering study. The Advisory Speed plaque shall only be used to supplement a warning sign and shall not be installed as a separate sign installation. The advisory speed shall be determined by an engineering study that follows established engineering practices.

CURVE ADVISORY SPEED WORKSHOP MUTCD 2009 Support: Among the established engineering practices that are appropriate for the determination of the recommended advisory speed for a horizontal curve are the following: A. An accelerometer that provides a direct determination of side friction factors B. A design speed equation C. A traditional ball-bank indicator using the following criteria: degrees of ball-bank for speeds of 20 mph or less degrees of ball-bank for speeds of 25 to 30 mph degrees of ball-bank for speeds of 35 mph and higher The 16, 14, and 12 degrees of ball-bank criteria are comparable to the current AASHTO horizontal curve design guidance. Research has shown that drivers often exceed existing posted advisory curve speeds by 7 to 10 mph. Source: FHWA MUTCD 2009

CURVE ADVISORY SPEED WORKSHOP MUTCD 2009 Guidance: The advisory speed should be determined based on free-flowing traffic conditions. Because changes in conditions, such as roadway geometrics, surface characteristics, or sight distance, might affect the advisory speed, each location should be evaluated periodically or when conditions change. Source: FHWA MUTCD 2009

CURVE ADVISORY SPEED WORKSHOP Horizontal Alignment Warning Signs (MUTCD 2003) Horizontal Alignment Horizontal Alignment + Advisory Speed Horizontal Alignment + Intersection One-Direction Large Arrow Chevron Alignment Truck Rollover Warning Advisory Speed Plaque Advisory Exit/Ramp Speed Source: FHWA MUTCD 2003

CURVE ADVISORY SPEED WORKSHOP Horizontal Alignment Warning Signs (MUTCD 2009) Horizontal Alignment Combination Horizontal Alignment + Advisory Speed Horizontal Alignment + Intersection One-Direction Large Arrow Chevron Alignment Truck Rollover Warning Advisory Speed Plaque Advisory Exit/Ramp Speed Horizontal Alignment + Advisory Exit/Ramp Speed Source: FHWA MUTCD 2009

CURVE ADVISORY SPEED WORKSHOP Horizontal Alignment Warning Signs (MUTCD 2003) relates sign usage to advisory speed and number of alignment changes less guidance Source: FHWA MUTCD 2003

CURVE ADVISORY SPEED WORKSHOP Horizontal Alignment Warning Signs (MUTCD 2009) revised significantly relates sign usage to the difference between the approach speed and the advisory speed hierarchical approach only for applications where advisory speed is less than posted Source: FHWA MUTCD 2009

CURVE ADVISORY SPEED WORKSHOP Current Practices to Determine Advisory Speed Driver Comfort Speed Ball-Bank Indicator 85 th Percentile Speed Geometric Design Other Approach

CURVE ADVISORY SPEED WORKSHOP Current Practices>> Driver Comfort Speed Oldest method used for determining advisory speeds. Defined in the 1930s as that “which causes an occupant of the vehicle to feel an outward pitch.” Engineers later refined the definition to be “that speed at which the driver’s judgment recognized incipient instability.” Drawbacks: most subjective and inconsistent results.

CURVE ADVISORY SPEED WORKSHOP Current Practices>> Ball-Bank Indicator A curved level filled with a dampening liquid with a trapped air bubble or “ball”. Installed in a test vehicle: multiple test runs at 5-mph increments. Indicate the geometric degree of “tip, tilt, or lean” of a curve roadway. Advisory speed is the highest test speed that does not exceed threshold. Most widely used instrument for determining advisory speeds by 82% of agencies (Lyles and Taylor, 2006).

CURVE ADVISORY SPEED WORKSHOP Current Practices>> Ball-Bank Indicator Varied Criteria May lead to different advisory speed recommendations. Speed Ball-Bank Threshold 2004 AASHTO2003 MUTCD2009 MUTCD ≤ 20 mph14˚ 16˚ mph12˚14˚ ≥ 35 mph10˚12˚ for Truck--10˚

CURVE ADVISORY SPEED WORKSHOP Wide variation in reading along curve –Expectation of constant reading along curve –May differ by directions based on superelevation Expected Relationship Current Practices>> Ball-Bank Indicator Data Source: TTI Horizontal Curve Signing Workshop (Nov 2008) Typical Relationship

CURVE ADVISORY SPEED WORKSHOP Current Practices>> Ball-Bank Indicator Sources of Variability Use of different test vehicles Personnel training Instrument calibration quality Speed Steering corrections –Tire slip Pavement variability –Roughness –Superelevation –Friction supply Can control Difficult to control Cannot control Data Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP Current Practices>> 85 th Percentile Speed Measuring speeds at which all drivers drive along a curve in a free flow condition. Set advisory speed at the level which 85% of all drivers drive at, or below. Represents the largest number of drivers within a narrow pace of 10 MPH. On target to provide the greatest level of safety for the majority.

CURVE ADVISORY SPEED WORKSHOP Current Practices>> 85 th Percentile Speed However, given direct measurements of curve speed distribution and vehicle classification, –No consensus on how to determine appropriate advisory speeds –85 th %, average, or median speeds? –Passenger cars, trucks or all? –What do you think? …… More discussion later –MUTCD 2009 no longer provides explicit support to this method

CURVE ADVISORY SPEED WORKSHOP Current Practices>> Geometric Design AASHTO calculates an advisory speed by: V² = 15 (e + f) R –Where: V = Advisory Speed of vehicle in MPH e = Superelevation in foot per foot of horizontal width f = Transverse coefficient of friction R = Radius of curvature in feet –Source of variability: value of transverse coefficient of friction.

CURVE ADVISORY SPEED WORKSHOP Current Practices>> Other Approach Example: Electronic Accelerometer –A gravity-sensitive electronic device –Measure the lateral forces and accelerations that drivers experience while traversing a highway curve. –Alternative to the ball-bank indicator. (AASHTO’s 2004 Green Book)

CURVE ADVISORY SPEED WORKSHOP New Procedures to Determine Advisory Speed Related TTI Projects (in cooperation with FHWA and the Texas DOT) – Identifying and Testing Effective Advisory Speed Setting Procedures (Project Director: Marla Jasek) Research Report ( ) Horizontal Curve Signing Handbook, 1st Edition ( P1) – Workshops on Identifying and Testing Advisory Speed Setting Procedures (Project Director: Darren McDaniel) Horizontal Curve Signing Handbook, 2nd Edition ( P1)

CURVE ADVISORY SPEED WORKSHOP New Procedures to Determine Advisory Speed Advisory Speed Criteria - Considerations –Car vs. truck speed –Average vs. 85 th percentile vs. Ball Bank Indicator reading –Curves are inherently unsafe, so advisory speed should be conservatively low –Drivers should feel advisory speed is reasonable –On sharp curves, 85 th percentile driver tends to adopt a speed that may be borderline unsafe Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP New Procedures to Determine Advisory Speed Advisory Speed Criteria - Recommendation –Average Truck Speed –Roughly equivalent to 40 th percentile car speed –Truck speed is generally 97% of car speed –Round to 5-mph increment Data Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP New Procedures to Determine Advisory Speed Direct Method Compass Method GPS Method Design Method

CURVE ADVISORY SPEED WORKSHOP New Procedures to Determine Advisory Speed Each Method involves the following two steps: 1.Data collection 2.Determination of Advisory Speed Direct calculation for Direct Method, or TTI Curve Speed Prediction Model for Compass, GPS, and Design Methods.

CURVE ADVISORY SPEED WORKSHOP New Procedures>> Direct Calculation Data Collection –Measure speed of 125 free-flow passenger cars Stop after 2 hours (radar) Stop after 4 hours (classifier) –Compute Average and 85 th percentile Speeds Determination of Advisory Speed –Average truck speed = 0.97 x average passenger car speed –Add one and drop down e.g. 34, 35, 36, 37, 38 → 35 mph; 39, 40, 41, 42, 43 → 40 mph Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP New Procedures>> TTI Curve Speed Prediction Model Compass MethodGPS MethodDesign Method –Compass –Ball-Bank Indicator –Distance-Measuring Instrument –GPS Receiver –Electronic Ball-Bank Indicator –Laptop Computer with TRAMS* –Plans of newly constructed or reconstructed curves Data Collection: * TRAMS: Texas Roadway Analysis and Measurement Software

CURVE ADVISORY SPEED WORKSHOP New Procedures>> TTI Curve Speed Prediction Model Determination of Advisory Speed Advisory speed is a function of curve deflection angle; superelevation rate; curve length; 85 th % speed (observed or estimated). Source: Horizontal Curve Signing Handbook (TTI, Oct 2008) Curve Geometry

CURVE ADVISORY SPEED WORKSHOP Curve Advisory Speed Worksheet An Excel® Spreadsheet based on and enhanced from Texas Curve Advisory Speed Software Calculates Advisory Speed for –Compass Method –GPS Method –Design Method Provides Curve Signing Guidelines for –TTI methods –Other sources (Accelerometer, AASHTO geometric design equation, Ball-bank indicator, 85 th % speed, driver comfort speed…) TTI Curve Speed Predication Model

CURVE ADVISORY SPEED WORKSHOP Curve Advisory Speed Worksheet Analysis –General Info. –Input Data –Alternate Input Data –Advisory Speed –Traffic Control Device Guidance

CURVE ADVISORY SPEED WORKSHOP Curve Advisory Speed Worksheet Analysis – General Info. –Input Data –Alternate Input Data –Advisory Speed –Traffic Control Device Guidance for Compass Method for GPS Method or Design Method for Advisory Speed from Other Source

CURVE ADVISORY SPEED WORKSHOP Curve Advisory Speed Worksheet Analysis –General Info. – Input Data –Alternate Input Data –Advisory Speed –Traffic Control Device Guidance Survey of Curve (Compass Method) Speed Limit

CURVE ADVISORY SPEED WORKSHOP Curve Advisory Speed Worksheet Analysis –General Info. –Input Data – Alternate Input Data –Advisory Speed –Traffic Control Device Guidance Curve geometry (GPS & Design Method) Curve surrounding features Tangent speed (optional data)

CURVE ADVISORY SPEED WORKSHOP Curve Advisory Speed Worksheet Analysis –General Info. –Input Data –Alternate Input Data – Advisory Speed –Traffic Control Device Guidance Advisory Speed by TTI model Advisory Speed from other sources Advisory Speed Selection

CURVE ADVISORY SPEED WORKSHOP Curve Advisory Speed Worksheet Analysis –General Info. –Input Data –Alternate Input Data –Advisory Speed – Traffic Control Device Guidance Warning signs (follow MUTCD 2009 guidelines)

CURVE ADVISORY SPEED WORKSHOP Confirm Advisory Speed and Curve Sign Selection Adjust the advisory speed or modify the warning sign layout based on consideration of: 1.driver approach sight distance to the beginning of the curve; 2.visibility around the curve; 3.position of the most critical curve in a sequence of closely-spaced curves. Source: Horizontal Curve Signing Handbook (TTI, Oct 2008)

CURVE ADVISORY SPEED WORKSHOP Confirm Advisory Speed and Curve Sign Selection 4.unexpected geometric features within the curve; presence of an intersection presence of a sharp crest curve in the middle of the horizontal curve sharp curves with changing radius (including curves with spiral transitions) sharp curves after a long tangent section broken-back curves Source: Horizontal Curve Signing Handbook (TTI, Oct 2008)

CURVE ADVISORY SPEED WORKSHOP Confirm Advisory Speed and Curve Sign Selection Approach Sight Distance Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP Confirm Advisory Speed and Curve Sign Selection Approach Sight Distance Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP Confirm Advisory Speed and Curve Sign Selection Visibility Around Curve Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP Confirm Advisory Speed and Curve Sign Selection Intersections or Driveways in Curve Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP Confirm Advisory Speed and Curve Sign Selection 3 curves in series Proximity to Other Curves: may influence curve speed Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP Confirm Advisory Speed and Curve Sign Selection Check Data Consistency –Consistent between opposing directions? Superelevation –Differ by 0 - 4% Radius –Within 10% in opposing directions Deflection angle –Within 2 degrees in opposing directions Smooth curve tracking is important –Consistent with judgment? 85 th percentile tangent speed or Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP Confirm Advisory Speed and Curve Sign Selection Example: –Radius and deflection angle are consistent –Superelevation differs by 7% –Consider re-driving the curve DirectionLeftRight Radius (ft) Deflection angle (deg)38 Superelevation (%)29 Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP Step by Step Procedure GPS Method Compass Method

CURVE ADVISORY SPEED WORKSHOP Step by Step Procedure>>GPS Method Equipment Setup Measurement Procedure Texas Roadway Analysis and Measurement Software (TRAMS) Program Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP Step by Step Procedure>>GPS Method Equipment Setup Laptop computer Electronic ball-bank indicator GPS receiver Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP Step by Step Procedure>>GPS Method Equipment Setup Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP Step by Step Procedure>>GPS Method Measurement Procedure seconds before start of curve Press space bar to start recording 2.Drive through one curve seconds after end of curve Press space bar to stop recording Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP Step by Step Procedure>>GPS Method Measurement Procedure –Track the centerline carefully –Choose slow but reasonable speed Rule of thumb: 10 mph below existing advisory speed No less than 15 mph No greater than 45 mph if superelevation is being measured Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP Step by Step Procedure>>GPS Method Device status Control button Curve & highway designation Curve data Texas Roadway Analysis and Measurement Software (TRAMS) Program Interface Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP Step by Step Procedure>>GPS Method TRAMS Curve Report File Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP Step by Step Procedure>>GPS Method TRAMS Curve Report File Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP Step by Step Procedure>>GPS Method Advisory Speed and Curve Signs

CURVE ADVISORY SPEED WORKSHOP Step by Step Procedure>>Compass Method Travel through the curve and collect data: Source: Horizontal Curve Signing Handbook (TTI, Oct 2008)

CURVE ADVISORY SPEED WORKSHOP Step by Step Procedure>>Compass Method Measurement Procedure 1.Record the regulatory speed limit and the curve advisory speed. 2.Stay in the same lane for all measurements. Record the curve deflection (left or right) relative to the direction of travel. Source: Horizontal Curve Signing Handbook (TTI, Oct 2008)

CURVE ADVISORY SPEED WORKSHOP Step by Step Procedure>>Compass Method Measurement Procedure 3.Advance the vehicle to the “1/3 point” (does not need to be precisely located). It is the point of partial curvature (PPC). Stop the vehicle and complete the following while at the PPC: Record the vehicle heading (in degrees). Press the Reset button on the DMI to zero the reading. Record the ball-bank indicator reading (in degrees). Record whether the ball has rotated to the left or right of the “0.0 degree” reading. Source: Horizontal Curve Signing Handbook (TTI, Oct 2008)

CURVE ADVISORY SPEED WORKSHOP Step by Step Procedure>>Compass Method Measurement Procedure 4.Advance the vehicle to the “2/3 point” (does not need to be precisely located). It is the point of partial tangency (PPT). Stop the vehicle and complete the following while at the PPT: Record the vehicle heading (in degrees). Press the Display Hold button on the DMI. 5.Record the value shown on the DMI which is the partial curve length. Source: Horizontal Curve Signing Handbook (TTI, Oct 2008)

CURVE ADVISORY SPEED WORKSHOP Step by Step Procedure>>Compass Method Advisory Speed and Curve Signs

CURVE ADVISORY SPEED WORKSHOP Step by Step Procedure>>Accelerometer Advisory Speed and Curve Signs

CURVE ADVISORY SPEED WORKSHOP Exercise 1 Objective: determine needed devices and advisory speed Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP Exercise 1 Speed limit: 60 mph Advisory speed: 45 mph Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP Exercise 1 Known Data: Regulatory speed limit: 60 mph Total deflection angle: 51 degrees Curve deflection angle: 17 degrees Superelevation rate: 6.5 percent Curve radius: 715 ft

CURVE ADVISORY SPEED WORKSHOP Exercise 1 Questions: What is the advisory speed? What warning signs are needed?

CURVE ADVISORY SPEED WORKSHOP Exercise 2 Objectives: determine needed devices and advisory speed Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP Exercise 2 Speed limit: 55 mph Advisory speed: 25 mph Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP Exercise 2 Known Data: Regulatory speed limit: 55 mph Total deflection angle: 83.9 degrees Curve deflection angle: 6.2 degrees Superelevation rate: 5.7 percent Curve radius: 278 ft

CURVE ADVISORY SPEED WORKSHOP Exercise 2 Questions: What is the advisory speed? What warning signs are needed?

CURVE ADVISORY SPEED WORKSHOP Exercise 3 Objectives: determine needed devices and advisory speed Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP Exercise 3 Speed limit: 60 mph Advisory speed: 50 mph Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP Exercise 3 Known Data: Regulatory speed limit: 60 mph Total deflection angle: 90 degrees Curve deflection angle: 8.3 degrees Superelevation rate: 5.5 percent Radius: 924 ft

CURVE ADVISORY SPEED WORKSHOP Exercise 3 Questions: What is the advisory speed? What warning signs are needed?

CURVE ADVISORY SPEED WORKSHOP Exercise 3 Discussion: Southbound approach has 5.5 percent downhill grade Review of crash data reveals crash problem on this approach (run-off- road near PC) May consider adding delineators Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP Exercise 4 Objectives: sensitivity analysis of guidance from Exercise 3 Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP Exercise 4 Speed limit: 60 mph Advisory speed: 50 mph Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP Exercise 4 Initial Data: Regulatory speed limit: 60 mph Total deflection angle: 90 degrees Curve deflection angle: 8.3 degrees Superelevation rate: 5.5 percent Radius: 924 ft Source: TTI Horizontal Curve Signing Workshop (Nov 2008)

CURVE ADVISORY SPEED WORKSHOP Exercise 4 For total deflection angles of 80, 90, 100 deg

CURVE ADVISORY SPEED WORKSHOP Exercise 4 Questions: What is the advisory speed? What warning signs are needed?

CURVE ADVISORY SPEED WORKSHOP Exercise 4 If the superelevation rate is 4, 5.5, 7 percent

CURVE ADVISORY SPEED WORKSHOP Exercise 4 Questions: What is the advisory speed? What warning signs are needed?

CURVE ADVISORY SPEED WORKSHOP Exercise 4 If curve radius is 874, 924, 974 ft

CURVE ADVISORY SPEED WORKSHOP Exercise 4 Questions: What is the advisory speed? What warning signs are needed?

CURVE ADVISORY SPEED WORKSHOP Exercise 4 For 85 th % tangent speed of 58 and 66 mph

CURVE ADVISORY SPEED WORKSHOP Exercise 4 Questions: What is the advisory speed? What warning signs are needed?

CURVE ADVISORY SPEED WORKSHOP Summary Importance of advisory speed and curve signing: SAFETY Advisory speed should be consistent with driver expectation. Devices should be uniform among curves of similar geometry, character, and road conditions. Current practices: lack of uniformity and inconsistent Proposed procedures: four new procedures to establish uniform and consistent advisory speed and curve signing. Comparable results among methods. Proposed procedures and software are uncomplicated and easy to implement, but still under further improvement.

CURVE ADVISORY SPEED WORKSHOP For More Information Development of Guidelines for Establishing Effective Curve Advisory Speeds – Horizontal Curve Signing Handbook, 2nd Edition – Texas Curve Advisory Speed Software – The 2009 Edition of the MUTCD –

CURVE ADVISORY SPEED WORKSHOP Contact Robert J. Milstead, PE, PTOE Vice President Brudis & Associates, Inc Rumsey Road, Suite C Columbia, MD Phone: (410) ext. 224 Fax: (410) The End Questions and Comments?