sj-5112 1011 3a sight distance

8/7/2019 SJ-5112 1011 3A Sight Distance

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SJ-5112 Perancangan Geometrik Jalan

Element of Design Sony Sulaksono Wibowo, Ph.D



Element of Design

o Sight Distanceo Horizontal Alignment

o

Vertical Alignmento Cross Section



Sight Distance

o

The length of the roadway a driver can see ahead at anyparticular time

o The ability of a driver to see ahead is crucial in the safe andefficient operation of a vehicle

o Sufficient sight distance must be provided at any point in thehighway to allow drivers of all skill levels traveling at designspeed to stop or maneuver around obstacles

o

Measurements of sight distance: Stopping Sight Distance (SSD)

Decision Sight Distance (DSD)

Passing Sight Distance (PSD)



Stopping SightDistance

Sight Distance

Decision SightDistance

Passing Sight Distance

Note: A driver’s ability to see ahead is of the utmostimportance in the safe and efficient operation of a vehicle on

a highway



Sight Distance

o Designer needs to consider a range of ability of drivers

Age – varies as you get older

Differences in sight, hearing and others

o Designer needs to consider different vehicles:

Compact car vs. large trucks or buses

Acceleration

Braking capabilities

Height of driver’s eye from ground

Ability to climb grades

Tire condition



Sight Distance

o The criteria used in sight distance include

Perception reaction time:

Perception of object on roadway

Identification of object Decision

Reaction/volition

Various studies on perception reaction time indicate that itvaries from 1.26 sec to 3 seconds depending on driver and object

Most agencies use 2.5 seconds (recommended by AASTHO) formost highway conditions

Longer times are required for more complex decisions



Stopping Sight Distance



Stopping Sight Distance (SSD)

o Distance ahead of the driver in which the driver can bring the vehicle to astop after seeing an object in the vehicle’s path without hitting the object

o Perception reaction distance (PRD):

distance traveled during the perception reaction time process

o

Braking distance (BD): distance to stop a vehicle once the brakes are applied

o Assumed Height:

the driver’s eye: 1,080 mm (3.5 ft)

the object to be seen: 600 mm (2.0 ft)

SSD = perception reaction distance + braking distance



Perception Reaction Distance

o

Studies: Johansson and Rumar (1971), “Drivers’ Break Reaction Times”,

Journal of Human Factors:

321 Drivers Median reaction time: 0.66 sec.

90th less than 1.5 sec.

MIT (1935), Report of Massachusetts Highway Accident:

Average: 0.64 sec. 95th less than 1.0 sec.

Normann (1953), “Braking Distances of Vehicles from HighSpeeds”, Proceedings Highway Research Board:

Brake reaction time: 0.4 to 1.7 sec.

those studieswere carried outat the simpleroadway

conditionfor unexpected

event the timecould increaseby 1 sec.



Perception Reaction Distance

o Studies: Fambro, Fitzpatrick, and Koppa (1997), “Determination of

Stopping Sight Distances. NCHRP Report 400:

Minimum brake reaction times should be at least 1.64 sec.

It was found that some drivers took over 3.5 sec.

90th less than 2.5 sec.

AASHTO (2001):

recommended to use 2.5 sec.

normal condition and unexpected event



Braking Distance

o Studies: Fambro, Fitzpatrick, and Koppa (1997), “Determination of

Stopping Sight Distances. NCHRP Report 400:

Most drivers decelerate at a rate greater than 4.5 m/sec2

Approximately 90% of all drivers decelerate at rates greater than3.4 m/sec2

AASHTO (2001):

Most vehicle braking systems and the tire-pavement friction levelsof most roadways are capable of providing a deceleration of at

least 3.4 m/sec2



Design Value of SSD

a

V t V SSD

2

2

+⋅=

a

V t V SSD

2

039.0278.0 +⋅=

Source: A Policy on Geometric Design of Highways

and Streets (The Green Book), Washington, DC.

American Association of State Highway and

Transportation Officials, 2001, 4th Ed.




Effect of Grade on Stopping

±

=

Ga

V SSDG

81.9

254

2

G is the percent ofgrade divided by 100







Decision Sight Distance (DSD)

o

The distance needed for a driver to detect an unexpectedor otherwise difficult-to-perceive information source

Requires higher perception-reaction time

Depends on type of maneuver made and roadway environment(e.g. urban or rural)

o Offers drivers additional margin of error and affords

them sufficient length to maneuver at the same orreduced speed, rather than just stop

o The values are substantially greater than Stopping SightDistance




Decision Sight Distance






Decision Sight Distance

o

For avoidance maneuvers A and B:

o For avoidance maneuvers C, D, and E:

o Note: In some instances, DSD may not be economically feasible.

In these cases, the use of suitable traffic control devices

should be provided

aV t V DSD

2

039.0278.0 +⋅=

t V DSD ⋅= 278.0



Passing Sight Distancefor two-lane highways




o

Important assumptions: The overtaken vehicle travels at uniform speed

The passing vehicle has reduced speed and trails the

overtaken vehicle as it enters a passing section

The passing vehicle accelerates during the maneuver andits average speed is 15 kph higher than the overtaken

vehicle

When the passing vehicle returns to its lane, there issuitable clearance length between it and the oncomingvehicle in the other lane



Passing Sight Distance – left side

right




PSD = d1 + d2 + d3 + d4

d1 = distance traveled during P/R time to point where vehiclejust enters the left lane

wheret1 = time for initial maneuver (sec)

v = average speed of passing vehicle (kph)a = acceleration (kph/s)m = difference between speeds of passing and passedvehicle (kph)

+−=

2

278.0 111

at mvt d




PSD = d1 + d2 + d3 + d4

d2 = distance traveled by vehicle while in right lane

where:v = speed of passing vehicle (mph)t2 = time spent passing in left lane (sec)

22 278.0 vt d =




PSD = d1 + d2 + d3 + d4

d3 = the clearance distance that varies from 30 to 75 m

d4 = distance traveled by opposing vehicle duringpassing maneuver

d4 usually taken as 2/3 d2










A i A i i f S Hi h d






from the previous slide



Passing Sight Distance (notes)

o Considering to provide passing sight distance along roadway

o Designers try to avoid long stretches with no passingopportunities as it leads to driver frustration

o A significant number of drivers may attempt to pass andattempt an unsafe maneuver

o Consider passing truck climbing lanes

o Need to consider traffic volumes

o Long trucks require additional time



Measuring Sight Distance



Driver Eye Height

Passenger Car: 1,080 mmLarge Trucks: 1,800 mm to 2,400 mm 2,330 mm

SD to Object

1,080 mm

Object

600 mm

Object

Criteria for Measuring Sight Distance



Measuring Sight Distance

sj-5112 1011 3a sight distance

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