Safety Impacts of Safety Impacts of Access Management Bill Eisele, - PDF document

5/12/2014 Safety Impacts of Safety Impacts of Access Management Bill Eisele, Ph.D., P.E. Bill Frawley, AICP Texas A&M ransportation Institute Meet Your Instructors Bill Eisele Bill Frawley Ph.D., P.E., Research Engineer AICP, Research Scientist Texas A&M Transportation Texas A&M Transportation Institute Institute Texas A&M University System Texas A&M University System Arlington, TX, USA College Station, TX, USA 1

5/12/2014 Course Objectives • Define access management • Describe the impacts of access management on crash rates / types • Describe how to perform a safety evaluation of an access management g treatment Course Overview 1. What is access management? 2. What are typical safety considerations and findings? 3. How can you perform a safety study? 4 4. Resource materials / contact info Resource materials / contact info 2

5/12/2014 Session 1 What is Access Management? What is Access Management? “….the systematic control of the location, spacing, design, and operation of i d i d ti f driveways, median openings, interchanges, and street connections to a roadway.” Transportation Research Board, Access Management Manual 3

5/12/2014 What is Access Management? • Balances access to land with traffic mobility needs mobility needs – Works with functional classification hierarchy • Set of tools to help protect public investments in roadways and improve safety f t Why Use Access Management? • Improve Public Safety • Enhance Mobility • Preserve Functional Classification Integrity • Protect Infrastructure Investment 4

5/12/2014 10 Principles of Access Management: Safety is Focus! 1. Ensure functional integrity 2. Limit direct access to major roadways 3. Promote intersection hierarchy 4. Locate signals to favor through movements 5. Preserve the functional area of intersections/interchanges Source: TRB AM Manual, see supplement 10 Principles of Access Management: Safety is Focus! 6. Limit the number of conflict points 7. Separate conflict areas 8. Remove turning vehicles from through-traffic lanes 9. Use nontraversable medians to manage left-turn movements 10.Provide a supporting street and circulation system Source: TRB AM Manual, see supplement 5

5/12/2014 Session 2 What are Typical Safety Considerations and Findings? Safety at the National Level 2011 US Fatalities 32,367 (motorists/nonmotorists) Fatality Rate per 100M VMT 1.10 Injury Rate per 100M VMT Injury Rate per 100M VMT 75 75 Source: National Highway Traffic Safety Administration 6

5/12/2014 How Access Management Improves Safety • Reduces Conflict Points at Intersections Reduces Conflict Points at Intersections – Driveways are Intersections too!! • Reduces Speed Differentials • Increases Driver Expectations Conflict Points Locations where the path of a car can cross the path of another car, bike, or pedestrian. 7

5/12/2014 4-Leg Intersection Conflict Points NHI Access Management Course Conflict Points Source: Texas A&M Transportation Institute 8

5/12/2014 3-Leg Intersection Conflict Points NHI Access Management Course Conflict Points with Raised Median NHI Access Management Course 9

5/12/2014 Conflict Points: Directional Raised Median = 1 Crossing =3 Diverge 3 Diverge =4 Merge 8 Total Source: TRB AM Manual Conflict Points: Non-motorized Source: TRB AM Manual 10

5/12/2014 Safety Considerations Access Spacing Unsignalized Access Spacing • Some engineering considerations: – Functional intersection area – AASHTO guidance – Stopping sight distance – Intersection sight distance – Case-by-case • Not a cookbook process! • Not a cookbook process! 11

5/12/2014 Functional Area of an Intersection (vs. Physical Area) Defined by Physical Area Defined by Functional Intersection Inappropriate Median Opening Source: Texas A&M Transportation Institute 12

5/12/2014 Queuing Through Signal Source: Texas A&M Transportation Institute AASHTO Says • Intersection functional areas extend beyond the physical boundaries beyond the physical boundaries • “Ideally, driveways should not be located within the functional area of an intersection or in the influence area of an adjacent j driveway” (AASHTO, 2011, “Green Book”, page 9-4) 13

5/12/2014 More from AASHTO • Driveway spacing should consider impacts that i ingress and egress actions have on through d ti h th h traffic • Impacts are measured by the distance at which through traffic slows or changes lanes due to a turning vehicle turning vehicle (AASHTO, 2004, Green Book, page 729) Intersection Sight Distance (enter / cross roadway) Si ht T i Sight Triangle l Line of Sight Driveway Source: TRB Access Management Manual, ITE Transportation and Land Development 14

5/12/2014 On-street Parking Obstruction Line of Sight Source: TRB Access Management Manual, ITE Transportation and Land Development Landscaping Obstruction I Inappropriate i t Landscaping Line of Sight Line of Sight Source: TRB Access Management Manual, ITE Transportation and Land Development 15

5/12/2014 Close Proximity Parking (problem) Driveway ROW Line Sidewalk Line of Sight (a) How do we fix this? Source: TRB Access Management Manual, ITE Transportation and Land Development Close Proximity Parking (solution) Driveway Landscaping ROW Line Sidewalk Line of Sight (b) Source: TRB Access Management Manual, ITE Transportation and Land Development 16

5/12/2014 Intersection Sight Distance (left turn from roadway) Line of Sight Sight Triangle Sight Distance Source: TRB Access Management Manual, ITE Transportation and Land Development Driveway Geometric Design Considerations • Adequate lighting • Driveway entry speed • Driveway entry speed – Speed differential and crash potential – Function of driveway radius – Functional of vertical curve • Design vehicle • Throat width and length Th t idth d l th • Driveway profile considering drainage Source: ITE Transportation and Land Development 17

5/12/2014 Corner Clearance • Where adequate space cannot be provided – May allow lesser spacing when shared May allow lesser spacing when shared access is allowed – Access may be allowed when no alternative exists, but at farthest location from intersection – Consideration given to right-in/right-out only g g g y operations • Involvement in platting process earlier helps to mitigate Good Corner Clearances Source: Texas A&M Transportation Institute 18

5/12/2014 Stopping Sight Distance Object > 2 feet high (e.g., brake lights of turning vehicle) Braking Distance Brake Reaction Distance Application of Access Criteria Stopping Sight Distance Example (Discussion Paper # 5C, Oregon DOT) 19

5/12/2014 Application of Access Criteria Stopping Sight Distance Example (Discussion Paper # 5C, Oregon DOT) Access Window Site “Window” for Left or Right Turn Right Turn Left Turn Source: ITE Transportation and Land Development 20

5/12/2014 Safety Considerations Raised Medians TWLTL Appropriate • Built out • • Low volume Low volume • Low access density Source: Texas A&M Transportation Institute 21

5/12/2014 TWLTL Breaking Down • Built out • High volume • High access density Source: Texas A&M Transportation Institute Why and When to Consider a Raised Median • Play critical role of operations and safety of roadway • Roadways where aesthetic considerations are a high priority • Multilane roadways with a high level of pedestrian activity • High crash locations or where it is desirable to High crash locations or where it is desirable to limit left turns to improve safety – Clear safety benefit Source: TRB AM Manual 22

5/12/2014 Keep in Mind . . . • Need adequate locations and width to handle U- turns turns – Can flare intersections or use loons – Alternative U-turn treatments • Alternate routes to handle delivery truck traffic Source: Texas A&M Transportation Institute Poll Question Do you have a 4-lane or 5-lane cross-section where a raised cross-section where a raised median would improve safety and/or mobility, but there is not adequate right-of-way to allow for U-turns? a) Yes b) No 23

5/12/2014 Poll Question Have you implemented flared intersections or similar midblock intersections or similar midblock treatments to allow U-turns where there is limited right-of-way? a) Yes b) No Safety Findings Access Density 24

5/12/2014 Safety • Reducing conflict points reduces crash potential • 50 to 55% related to intersections 50 to 55% related to intersections • 60% in urban areas • 40% in rural areas • Remember, driveways are intersections too! Percentage of Crashes by Movement Source: TRB AM Manual 25