W3 L CIVE7796

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Swinburne University of Technology *

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Mechanical Engineering

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Oct 30, 2023

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Speed Parameters & Sight Distance CIVE7796
RMIT Classification: Trusted Speed Parameter “A fundamental aim of road design is to provide a road system and environment that contributes to the prevention of vehicle crashes, particularly those involving fatalities and serious injuries, as well as satisfying the expectation of and need for efficient transportation.” (Austroads- Guide to Road Design, Part 3) 2
RMIT Classification: Trusted Speed Parameter Operating speed Desired speed Design speed Relationship with each other 3
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RMIT Classification: Trusted Speed Parameter Operating Speed ( speed to use for design ) The speed to be adopted, which typically provides some margin over the proposed posted speed limit , directly influences the principal parameters used in road design which include: sight distance stopping distance horizontal curve radii pavement superelevation traffic lane width. There should certainly be ‘no surprises’ for drivers, such as an isolated sharp curve in a section of road where all other curves have large radii. 4
RMIT Classification: Trusted Speed Parameter Operating Speed ( speed to use for design ) There should certainly be ‘no surprises’ for drivers, such as an isolated sharp curve in a section of road where all other curves have large radii For rural roads where it is not practicable to achieve consistent geometry and a uniform operating speed throughout their length it is necessary to safely manage changes in speed of vehicles between different sections of road The design speed for a road or section of road should not be less than the measured or estimated operating speed 85th Percentile of low traffic volume speed 5
RMIT Classification: Trusted Speed Parameter Desired Speed (V desired ) is the speed that drivers will adopt or operate at on the less constrained alignment elements of a reasonably uniform section of the road. It is influenced by: roadside environment topography in rural areas, development density and type (i.e. built environments) in urban areas road characteristics geometric standard (predominately horizontal alignment; to a lesser extent, vertical alignment; and lane widths), frequency of intersections and accesses, sight distance, parking provisions etc. speed limit road function to the extent that on important roads such as motorways and highways, drivers are less willing to accept reductions in desired speed 6
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RMIT Classification: Trusted Speed Parameter Desired Speed State and territory road agencies have policies and guidelines for the setting of speed limits On urban arterial roads, the primary factors influencing the desired speed are roadside environment and speed limit When road constrains are removed divers will quickly accelerate back to the desired speed 7
RMIT Classification: Trusted Speed Parameter Design Speed (V design ) is equal or greater than the Operating Speed for the particular horizontal geometric element and used for the calculation of various geometric design parameters. Fixed speed for geometric design Used for the calculation of various geometric design parameters (e.g. sight distance, application of super elevation, horizontal and vertical curve radii) should not be less than the expected operating (85th percentile) speed for the road If the operating speed varies along the road, the design speed may vary accordingly 8
RMIT Classification: Trusted Speed Parameter Vehicle Speed high speed: 90 km/h or greater intermediate: 70 to 89 km/h low speed: 69 km/h or less 9
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RMIT Classification: Trusted Speed Relationship 10 Figure 3.1: Speed relationship diagram
RMIT Classification: Trusted Sight Distance the distance over which visibility occurs between a driver and an object- single vehicle sight distance between two drivers at specific heights above the carriageway 11
RMIT Classification: Trusted Sight Distance Parameters Assumptions for parameters • object height • driver eye height • driver perception reaction time 12
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RMIT Classification: Trusted Sight Distance Parameters Object Height object height is a compromise between the length of sight distance and cost Table 5.1 is used 13
RMIT Classification: Trusted Sight Distance Parameters: Object Height 14
RMIT Classification: Trusted Sight Distance Parameters: Object Height Table 5.1: Vertical height parameters 15
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RMIT Classification: Trusted Sight Distance Parameters Drivers Eye Height » combination of the height of driver stature and driver seat height listed in Table 5.1 car driver eye height should be 1.10 m commercial vehicle and truck driver eye height should be 2.40 m bus driver eye height should be 1.80 m 16
RMIT Classification: Trusted Sight Distance Parameters driver perception reaction time Time to perceive and react to a stimulus and take appropriate action Reaction time depends on alertness of the driver recognition of the hazard complexity of the decision or task involved Desirable reaction is 2.5 seconds 17
RMIT Classification: Trusted Sight Distance Parameters: Reaction Time 18
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RMIT Classification: Trusted Sight Distance Parameters Longitudinal deceleration (d) measure of the longitudinal friction between vehicle tyres and road surface most urban and rural roads, d = 0.36 Use Table 5.3 For unsealed roads & design vehicle cars, use Table 5.4 19
RMIT Classification: Trusted Table 5.3: Design domain for coefficient of deceleration 20
RMIT Classification: Trusted Sight Distance Parameters: Longitudinal deceleration 21
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RMIT Classification: Trusted Sight Distance Parameters Stopping sight distance (SSD) » T he distance that alert driver, travelling at design speed on wet pavement, to perceive, react and brake to a stop before reaching a hazard » Two components distance travelled during the total reaction time distance travelled during the braking time from the design speed to a stop 22
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RMIT Classification: Trusted Sight Distance Parameters Stopping sight distance (SSD) » The relationship Where, R T is the reaction time (sec) V is the operating speed (km/h) d is the coefficient of deceleration a is the longitudinal grade (%; ‘+’ for up - grades, ‘ - ’ for down-grades) » The value of R T and d must be assumed » Use Table 5.2 and Table 5.3 respectively 23
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RMIT Classification: Trusted Sight Distance Parameters: Stopping Sight Distance » Car SSD measured between the driver’s eye (1.1 m) and a 0.2 m high, stationary object on the road Use Table 5.5 24
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RMIT Classification: Trusted Table 5.5: Stopping sight distances for cars on sealed roads 25
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RMIT Classification: Trusted Questions? 26
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