1. Basic Design Review Fall 2017
A few slides were taken from CVEN 307 originally prepared by Dr. Gene H. Hawkins.

2. Basic Principles Road Network:
Carries motorized and non-motorized traffic.
Is part of the overall transportation network, which includes rail, waterways and aviation.
Plays an essential part in developing urban and rural areas.
The task of road network design is to arrange and design individual road sections according to their respective functions within the scope of transportation and regional planning.
Traffic related functions (mobility/access) versus non- traffic related functions (local/pedestrian use).

3. Historical Perspective
• Oldest known highway: The Faiyumhollow located 70 km south of Cairo, Egypt (4,600 BC). This was 13-km road (naturally paved) linking a quarry to the Nile.
• The Greeks were the first to establish “law of road construction” setting minimum vehicle track width at 4ft-4in.
• First paved roads were called procession roads located near temple and holy places. Some were designed with tracks for the movements of wagons.

4. Historical Perspective
• Early road networks:
Trade and Religious
Military:
* Extensive, fast relocation of armies to quell rebellions
* Easily spreading important news throughout the empire
* Safe and effective transport of tributes from conquered nations.

5. Historical Perspective
• Romans:
* Road construction and design were very advanced (400,000 km at its height of power; 80,00 km of excellent quality)
*Straight and elevated, if possible (to dominate the surroundings)
* 10% maximum grade
* Did their design affected current
traffic fatalities in London?

6. Historical Perspective
Romans’ highway network illustrated as a subway map

7. Historical Perspective
• In 1835, lectures about road construction trackage engineering were part of the engineering program at University of Karlsruhe (new name).
• In 1887, Launhartd wrote the “Theory of the Alignment”, which included a discussion about circular curves.
• In 1920, Euting wrote “The Construction of Rural Roads”. This manual include information maximum grades for different types of terrain and cross-sections.

8. Wright and Dixon (2004) Figure 1-3

9. Role of Highways
The two considerations in classifying highway and street networks functionality are 1) travel mobility and 2) access to property
Mobility: To provide users with means to travel from a point of origin to a point of destination the most efficient and safest way possible
Access: To provide users access to services and property the most efficient way possible

10. Road Functions Roads serve one of two functions Basis for design
Mobility (higher class)
Access (lower class)
Cannot serve both functions well
Basis for design
Design for function, not volume
Very important!

11. Wright and Dixon (2004) Figure 1-2

12. Maze et al. (2000) Figure 5

13. Factors that Affect Design
Vehicles
Type of Vehicle
Proportion in Traffic Stream
Driver
Older Drivers
Roadway
Volume
Speed
Features
Vehicles
Planes, trains, autos,
buses, ships, trucks
Infrastructure
Road, canal, rail, air
Transfer points
Supporting elements
(signs, signals, safety)
Operators/Content
Drivers, pilots, freight,
passengers

14. Design Process STEPS EXAMPLES PROCESS Freeway vs Arterial Tollway
Express vs Local Transit
Type of
Facility
Planning
Size of
Facility
Traffic Design
# of Lanes
# of Runways
Alignment
Configuration/Orientation
Environmental Impact Assessment
Preliminary
Design
Location

15. Design Process (Cont.) STEPS EXAMPLES PROCESS Design Speed
Design Vehicle
Design Driver
Identify
Standards
Physical Design
Plans,
Specification,
& Estimates
(PS&E)
Physical Design
Geometric Features
Surface/Guideway Design
Auxiliary Systems
Construction
Materials
Structures
Construction

16. Wright and Dixon (2004) Fig 13-1

17. Speed Definitions
Design Speed – a selected speed used to determine the various geometric features of the roadway. The assumed design speed should be a logical one with respect to the topography, anticipated operating speed, the adjacent land use, and the functional classification of the highway.
Operating Speed – speed of vehicles in free flow conditions
Space mean speed (distance/time)
Running Speed – speed at which vehicle travels over a highway section
Time mean speed (spot speed over time)
Posted Speed – speed limit
85th percentile of time mean speed (in theory)

18. Design Controls
Vehicles
Drivers
Dimensions
Driving Task
Performance
Guidance Task
Pollution
Driver Expectancy

19. Stopping Sight Distance
Definition: The available sight distance on a highway that allows a vehicle traveling near the design speed to stop before reaching a stationary object in its path
Brake Reaction Time (d1)
Braking Distance (d2)

20. Passing Sight Distance
Definition: The sight distance needed for allowing a faster vehicle to pass a slower vehicle on a two-lane highway
Sum of four distances:
d1 – Distance traversed during the perception and reaction time + acceleration to the point of encroachment
d2 – Distance traveled while the passing vehicle occupies the left lane
d3 – Distance between the passing vehicle at the end of its maneuver and the opposite vehicle
d4 – Distance traversed by an opposing vehicle for 2/3 of the time the passing vehicle occupies the left lane

21. Passing Sight Distance
Initial Maneuver Distance
Clearance Distance
Opposing Vehicle Distance
Occupying Left-Lane Distance

22. Passing Sight Distance
6th edition only provides values. It does not separate the analysis in 4 parts.

23. Horizontal Alignment

24. Superelevation Design
Desirable superelevation:
for R > Rmin
Where,
V= design speed in ft/s or m/s
g = gravity (9.81 m/s2 or 32.2 ft/s2)
R = radius in ft or m
Various methods are available for determining the desirable superelevation, but the equation above offers a simple way to do it. The other methods are presented in the next few overheads.

25. Methods for Estimating Desirable Superelevation
Superelevation and side friction are directly proportional to the inverse of the radius (straight relationship between 1/R=0 and 1/R =1/Rmin)
Method 2:
Side friction is such that a vehicle traveling at the design speed has all the acceleration sustained by side friction on curves up to those requiring fmax
Superelevation is introduced only after the maximum side friction is used

26. Method 3: Method 4: Method 5:
Superelevation is such that a vehicle traveling at the design speed has all the lateral acceleration sustained by superelevation on curves up to those required by emax
No side friction is provided on flat curves
May result in negative side friction
Method 4:
Same approach as Method 3, but use average running speed rather than design speed
Uses speeds lower than design speed
Eliminate problems with negative side friction
Method 5:
Superelevation and side friction are in a curvilinear relationship with the inverse of the radius of the curve, with values between those of methods 1 and 3
Represents a practical distribution for superelevation over the range of curvature
This is the method used for computing values shown in Exhibits 3-25 to 3-29

27. Five Methods fmax e = 0 emax f M2 M1 M5 M3 1/R M4 Side Friction Factor
Reciprocal of Radius
1/R M4

28. Superelevation Design for High Speed Rural and Urban Highways

29. Transition Design Control
Tangent Runout

30. Transition Design Control
Superelevation Runoff

31. Transition Design Control

32. Transition Design Control

33. Minimum Length of Superelevation Runoff

34. Minimum Length of Superelevation Runoff
∆ = relative gradient in previous overhead

35. Minimum Length of Superelevation Runoff
Values for n1 and bw in equation

36. Minimum Length of Tangent Runout
See Exhibit 3-32 for values of Lt and Lr

37. Superelevation Runoff

38. Vertical Curve A = G2 – G1 K = L / |A| Rate of change of grade Offset
y = 4E(x/L)2
Offset
External Distance
E = M = A L / 800
Vertical Point of Intersection
Ele. of P = [ele. Of VPC + (G1 / 100) x] + y
X = L|G1|/ (|G1 – G2|) (high or low point)
Vertical Point of Tangency
Vertical Point of Curvature

39. Criteria for Measuring Sight Distance
Driver Eye Height
Passenger Car: 3.5 ft
Large Trucks: 5.9 to 7.9 ft
SSD Object
2.0 ft
PSD Object
3.5 ft
Object

40. Measuring Sight Distance

41. Vertical Crest Curve

42. Vertical Crest Curve

43. Vertical Sag Curve

44. Vertical Sag Curve

45. Vertical Sag Curve

46. Vertical Sag Curve

47. Vertical Sag Curve
S > L:

48. Vertical Sag Curve
S < L:

49. Theoretical Application of Method 5 (with example)

50. Selection of fdesign and edesign (Method 5)
fmax (for the design speed)
Side Friction Factor
e = 0
fdesign
emax (for the design speed)
Reciprocal of Radius
1/R

51. Selection of fdesign and edesign
Rf = V2/(gfmax)
Rmin = V2/[g(fmax + emax)]
fmax
Side Friction Factor
e = 0
fdesign
emax
Ro = V2/(gemax)
Reciprocal of Radius
1/R
R0: f = 0, e = emax

52. Selection of fdesign and edesign
fdesign = α(1/R)+β(1/R)2
fmax (for the design speed)
Side Friction Factor
α = fmaxRmin[1-{Rmin/(R0-Rmin)}]
e = 0
fdesign
β = fmaxRmin3/(R0-Rmin)
emax (for the design speed)
Reciprocal of Radius
1/R

53. Example:
Design Speed: 100 km/h
fmax = 0.128
emax = 0.06
Question?
What should be the design friction factor and design superelevation for a curve with a radius of 600 m?

54. 1. Compute Rf, R0, and Rmin:
Rf = V2/(gfmax) = / (9.81 x 0.128) = 615 m
R0 = V2/(gemax) = / (9.81 x 0.06) = 1311 m
Rmin = V2/[g(fmax + emax)] = / [9.81( )]
Rmin = 418 m

55. Selection of fdesign and edesign (example)
fmax = 0.128
Side Friction Factor
e = 0
fdesign
emax = 0.06
1 / 1311
1 / 615
1 / 418
1/R

56. 2. Compute α and β:
α = x 418 x [1 – 418 / (1311 – 418) ] = m
β = x 4183 / (1311 – 418) = 10,502 m2
3. Compute fdesign and edesign :
First, estimate the right-hand side of equation for designing superelevation
e + f = V2/(gR) = / (9.81 x 600) = 0.131
Then,
fdesign = / / 6002 = 0.076
edesign = – = (< emax = 0.06)

57. Selection of fdesign and edesign (example)
fmax = 0.128
Side Friction Factor
e = 0
fdesign
emax = 0.06
0.076
1 / 1311
1 / 615
1 / 418
1/R
1 / 600

58. Selection of fdesign and edesign (example)
R=600 ft