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# 3-D Sight Distance Assessment in Road Design

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Analytical 3-D calculation of sight distances that prove to mitigate the resulting sight distance calculation errors based on the conventional 2-D calculation approach.

Presented at the Road Safety & Simulation Conference in Rome 2013

Published in: Design, Technology, Business
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### Transcript of "3-D Sight Distance Assessment in Road Design"

1. 1. 4th International Conference on Road Safety and Simulation RSS 2013 23rd-25th October 2013 Rome, Italy Analytical Method for Three-Dimensional Stopping Sight Distance Adequacy Investigation Fotis Mertzanis Antonis Boutsakis Rural and Surveying Eng. MSc, PhD Candidate Civil Eng. Research Associate Stergios Mavromatis Assistant Professor Technological Educational Institute of Athens Ikaros Kaparakis Civil Eng. Research Associate Basil Psarianos Professor National Technical University of Athens
2. 2. Stopping Sight Distance (SSD) Approach  2D inexact – fragmentary ► negative impact ► cost (excessive overdesign suggestions) ■ design consistency (unnecessary posted speed areas) ■  3D ► integrated
3. 3. Current Practice  2D approach ► efforts to overcome this incorrect SSD determination ■ establishing some coordination between the horizontal and vertical curve positioning – e.g. vertical transition curve should be entirely designed inside the horizontal curve [Green Book (2011)] ■ not all design cases are addressed
4. 4. SSD Modeling  2D and 3D models ► ► ► capable of simulating accurately compound road environments (3D) allow the definition of actual vision field to driver (3D) focused in optimizing the available SSD ■ ■ introducing new algorithms design parameter combinations
5. 5. Objectives  simulate from a 3-D perspective concurrently ► ► alignment design vehicle dynamics on the road surface during emergency braking conditions  point out design elements responsible for SSD inadequacies ► providing precious guidance to the designer for further alignment improvement
6. 6. Methodology  SSDdemanded calculation ► 3D road environment ► vehicle dynamics  SSDavailable calculation ► 3D road environment ► define areas where line of sight intersects roadway or cross sectional elements
7. 7. SSDdemanded Calculation 𝟐 𝑽𝒐 𝑺𝑺𝑫 = 𝑽 𝒐 𝒕 + 𝒂 𝟐𝒈 + 𝒔 𝒈 where : Vo (m/sec) : vehicle initial speed t (sec) : driver’s perception – reaction time g (m/sec2) : gravitational constant a (m/sec2) : vehicle deceleration rate s (%/100) : road grade [(+) upgrades, (-) downgrades] (1/5)
8. 8. SSDdemanded Calculation 𝟐 𝑽𝒐 𝑺𝑺𝑫 = 𝑽 𝒐 𝒕 + 𝒂 𝟐𝒈 + 𝒔 𝒈 where : Vo (m/sec) : vehicle initial speed t (sec) : driver’s perception – reaction time g (m/sec2) : gravitational constant a (m/sec2) : vehicle deceleration rate s (%/100) : road grade [(+) upgrades, (-) downgrades] (2/5)
9. 9. SSDdemanded Calculation  enriched model of SSD determination ► actual friction in the longitudinal direction 𝒇𝑻 = 𝒂 𝒈 𝟐 − 𝑽𝟐 − 𝒆 𝒈𝑹 𝟐 where : fT : friction demand in the longitudinal direction of travel V (m/sec) : vehicle (design) speed a (m/sec2) : vehicle deceleration rate g (m/sec2) : gravitational constant R (m) : horizontal radius e (%/100) : road cross – slope (3/5)
10. 10. SSDdemanded Calculation  (4/5) enriched model of SSD determination ► grade effect on vertical curves 𝑽 𝒊+𝟏 = 𝑽 𝒊 − 𝒈 𝒇 𝑻 + 𝒔 𝒕 𝟏 𝑩𝑫 𝒊 = 𝑽 𝒊 𝒕 − 𝒈 𝒇 𝑻 + 𝒔 𝒕 𝟐 𝟐 where : Vi (m/sec) : vehicle speed at a specific station i Vi+1 (m/sec) : vehicle speed reduced by the deceleration rate for t = 0.01sec t (sec) : time fragment (t = 0.01sec) s (%/100) : road grade in i position [(+) upgrades, (-) downgrades] fT : friction demand in the longitudinal direction of travel BDi (m) : pure braking distance g (m/sec2) : gravitational constant
11. 11. SSDdemanded Calculation  (5/5) enriched model of SSD determination ► ► actual friction in the longitudinal direction grade effect on vertical curves 𝑺𝑺𝑫 𝒅𝒆𝒎𝒂𝒏𝒅𝒆𝒅 = 𝑽 𝒐 𝒕 + 𝑩𝑫 𝒊 where : Vo (m/sec) : vehicle initial speed t (sec) : driver’s perception – reaction time 𝐁𝐃 𝐢 (𝐦): total vehicle pure braking distance for the initial vehicle speed
12. 12. SSDavailable Calculation (1/6)  line of sight between driver – obstacle positioned at any desired offset and any predefined heights  identify areas where line of sight intersects roadway or cross sectional elements
13. 13. SSDavailable Calculation (2/6) roadlines  lines running longitudinally across the roadway that split the road into areas of uniform or linearly varied transverse slope x-section view plan view
14. 14. SSDavailable Calculation  (3/6) roadline calculation step is user-specified and delivers a number n of cross-sections ► n is defined as the total roadway length divided by the selected calculation step  roadline coordination performed on every cross-section  a network of triangles representing the roadway surface as well as other distinctive parts is created ► connecting a point on one roadline with two relative points on an adjacent roadline
15. 15. SSDavailable Calculation (4/6)
16. 16. SSDavailable Calculation (5/6)
17. 17. SSDavailable Calculation Line of Sight – Obstacle Intersection  analytical geometry (6/6)
18. 18. SSD Adequacy SSDdemanded ≤ SSDavailable
19. 19. SSD Adequacy Investigation Flow Chart SSDdemanded definition initial speed driver position (j) road environment 3D road environment digital terrain model plan view longitudinal profile cross - sections calc. step definition i driver’s line of sight until position i uninterrupted driver – object heights i=i-Δi SSDavailable definition roadside elements (barriers, walls, cuts – fills etc.) SSDi, available temporary definition i=i+Δi driver’s line of sight until position i interrupted SSDdemanded ≤ SSDavailable ΟΚ SSDdemanded > SSDavailable PROBLEM record position
20. 20. Case Study  right branch section (L=4.3km) divided highway
21. 21. Case Study  right branch section (L=4.3km)  Vdesign = 120km/h  open roadway  tunnel ►  Ltunnel = 1,250m (St.3+000 – St.4+250) passing lane divided highway
22. 22. Case Study open roadway x-section   assumptions tunnel x-section tunnel advisory speed = 100km/h tunnel effective length ► ► 300m in advance of the entering portal extra 200m segment transition zone ahead Vvehicle=120km/h → Vvehicle=100km/h  fwet = 0.38 (decelarationwet = 0.38 x g m/sec2 )  fdry = 0.65 (decelarationdry = 0.65 x g m/sec2 )
23. 23. Case Study longitudinal profile
24. 24. Case Study SSD Adequacy Investigation outputs
25. 25. Case Study SSD Adequacy Investigation
26. 26. Case Study SSD Adequacy Investigation
27. 27. Case Study SSD Adequacy Investigation
28. 28. Case Study SSD Adequacy Investigation
29. 29. Case Study SSD Adequacy Investigation
30. 30. Case Study SSD Adequacy Investigation
31. 31. Case Study SSD Adequacy Investigation
32. 32. Conclusions  accurate SSD adequacy investigation ► ►  based on the difference between SSDavailable - SSDdemanded applied in any 3-D road environment flexibility among every road design and/or vehicle dynamic parameter inserted  direct overview regarding design elements responsible for SSD inadequacies  accurate aid to implement geometric design control criteria
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