basics aspects of traffic engineering

1. TRAFFIC
ENGINEERING
By: Anjani kumari
Cuj/I/2013/IWEM/018

2. Traffic volume = no. of vehicle per unit time
Trend chart = a graph of traffic volume vs year
AADT = (no. of vehicle/365)
Travel time = it is the efficiency of road.
Running speed = total distance travelled
running speed
Travel/journey/overall speed = total dis.Travelled
total time
Note: total time means including all stops and
delays
TRAFFIC STUDIES AND ANALYSIS

3.  Travel time: it is inversely related to speed. It is a
measure of efficiency of road.
 Avg. Speed: it is the avg of spot speeds of all
vehicle.
 Space mean speed: avg. Speed of vehicle in a
certain road length at any time.
Vs = 3.6dn/ where i= 1,2,3........n
 Time mean speed: represents the speed
distribution of vehicle at a point on a roadway
Vt = /n where i = 1,2,3...........n
d = length of road, ti and vi = observed travel time and
instantaneous speed for ith vehicle
Ʃti
ƩVi

4.  Variation chart: it shows hourly daily or seasonal
variation.
 volume flow diagram: no. of vehicle entering the
traffic = no. of vehicle going out traffic
 Design hourly volume: it is determined by plot
between hourly volume and no. of hours in a
year that the traffic volume exceeded.
30th highest hourly volume : it is hourly volume
that will v reached only 30 times and exceeded
only 29 times in a year and all other values are
less. It is adopted in India for design purposes..

5.  Spot speed: instantaneous speed at a particular
section or location.
Most commonly used method is “Radar method”.
Other methods are:
Endoscope/Mirror box method
Electronic method
Photographic method.
Model speed: speed at which max no. Of vehicle
moving. Determine by a plot between frequency
and speed.

6. Model speed
Frequency%
Speed
Cumulative speed distribution curve
Cumulative
Frequency%
98th percentile speed (design speed)
85th percentile speed (upper safe limit)
Modalspeed
15th percentile speed (lower safe limit)
50th percentile speed (middle speed)
Speed

7. Speed and delay analysis
Floating car/ riding deck method:
A car and 4 observer are there.
1st observer is at the car with 2 stopwatches.
1 for measuring time at various control points like
intersections
Other for duration of individual delay
2nd observer notes the time location and cause of
delay.
3rd observer counts the no. of vehicles overtaking the
test vehicle and overtaken by the test vehicle
respectively.
4th observer counts the no. of vehicle coming in
opposite direction.

8. t = tw-ny/q
q = na + ny
tw + ta
Where,
t = avg. journey time in min.
q = no. of vehicle per min.
tw = no. of vehicle when test vehicle running with
stream
ta = no. of vehicle when teat vehicle running
against stream
na = vehicles counted in opposite direction
ny = overtaking vehicle - overtaken vehicle

9. Origin and destination studies
 Desire line: a line connecting origin to
destination.
 Different methods for this are:
Road side interview
Home interview
License plate method
Tag or car method
Return post card method

10. Traffic volume = no. Of vehicle moving in a
specified direction on a given lane that passes a
given point during a specified unit of time.
Traffic density = no. Of vehicle occupying a unit
length of lane of a roadway at a given instant.
Highway capacity = ability of roadway to allow
maximum traffic flow per unit time.
traffic volume = traffic density * traffic speed
q = k.v
q = vehicle per hour, k = vehicle per kilometre,
v=kilometre per hour.

11. Speed Volume
Density Density (kj)
q,max = (Vsf/2*Kj/2)
Volume = (Vsf*Kj)/4
Vsf= free mean speed
Kj = max jam density
speed q,max = max traffic volume

12.  Space headway: head to head space interval
between the passage of successive vehicle
moving in a same lane.
 Time headway: head to head time interval
between the passage of successive vehicle
moving in a same lane.
Space time
headway headway
speed
speed

13. Type of traffic capacity
 Basic capacity : max. possible volume of
traffic in most ideal condition.
 Possible capacity : In worst condition = 0
In ideal condition = basic capacity
 Practical capacity = also called design
capacity
max. no. of vehicle that can pass through a
point on a roadway during one hour without
traffic density or any delay.

14. Theoretical maximum capacity
C = (v/s)*1000
C = theoretical max capacity (veh/hr)
V = velocity (kmph)
S = space headway (m)
S = SSD + L
SSD = vt + (v2 /2gf)
S = 0.7v + L , v in m/s, L in m and S in m
S = 0.2 v + L, v in kmph, L in m and S in km

15. PCU
Passenger car unit : to convert the mixed traffic
of different vehicle classes into a standard
vehicle unit.
PCU = capacity of road when passenger cars only
capacity of road when there are vehicle of
o same classes
Car/ auto, pcu = 1

16. Accident analysis
1.When moving vehicle hits the moving object like
parked vehicle.
2.Two vehicle collides at intersection (90 degree)
3.When moving vehicle with stationary object like
rigid structure.
4. Rear end collision of two vehicle.
5. Head- on collision of two vehicle approaching
from opposite direction.
6.Vehicle collides with a stationary object which is
collapsible like electric pole.

17. CASE 1
Before collision after collision
 v₁2 - v₂2 = 2gfs₁
 Ma*V₂ + Mb*0 = (Ma + Mb)V₃
 V₃2 – 02 = 2gfs₂
A AA A BBB
V₁ V₂ V₃ V₃ V₄=0
S₁ S₂

18. A A
B
B
B
ᶱA
ᶱB
SA₁
SB₁
VA₁ VA₂
VB₁VB₂
W E
S
N
CASE 2

19. CASE 2
 Va₁2 -Va₂2 = 2gfSa₁
 Vb₁2 -Vb₂2 = 2gfSb₁
Along E-W diection:
 Ma*Va₂ + Mb*0 = Ma*Va₃*cos + Mb*Vb₃*sin
Along N-S direction:
 Mb*Vb₂ + Ma*0 = Ma*Va₃*sin + Mb*Vb₃*cos
 Va₃2 = 2gfSa₃
 Vb₃2 = 2gfSb₃
ᶿᴀ
ᶿB
ᶿA ᶿB

20. TRAFFIC CONTROL DEVICES
 Signals
 Signs
 Road marking
 Rotary intersection
1.Traffic signals are automatic traffic devices
which could direct the traffic to stop, to ready
to proceed and to proceed by using red
yellow/amber and green light as per
predetermined time setting

21. Cycle length : a complete cycle of indication of a
signal in sec. i.e, a start of green light to next
green indication.
Interval: change of 1 stage to another
Change interval : indicate interval b/w green
and red (yellow time).
Clearance interval : all red time
Green interval: actual duration, the green light
of the traffic is turned on.
Red interval: actual duration, the red of the
traffic is turned on.
Phase: a phase is green interval + change &
clearance interval.

22. Design of signals
1. trial cycle method
2. approximate method
3. webster method
4. IRC method
Trial cycle :
G₁ = (2.5 n₁ C₁/900), G₂ = (2.5 n₂ C₂/900)
C₁’ = G₁ + G₂ + A₁ + A₂
Where, n₁ & n₂ are the 15 min.(900 sec.) traffic counts on road
1 & 2
2.5 is the assumed avg.Time headway
C₁ is assumed trial cycle length
C₁’ is calculated cycle length
A₁ & A₂ are amber time either assumed or calculated
If C₁ & C₁’ are appox. Equal then c₁ accepted for design.

23. Approximate method
Based on pedestrian walking speed of 1.2m/s and
the roadway width of each approach road a &
b. Lets width beWa &Wb, the C.I clearance
time (minimum time for pedestrian to cross
road) is calculated.
1. C.I =Wb/1.2 for road A &Wb/ 1.2 for road .
2. Total pedestrian crossing time(R) = C.I + 7 sec.
7 sec. Is minimum initial interval for pedestrian to
start crossing. R = red time.
Total red time = green time + amber time
3. Ga = Ra +Aa , Gb = Rb +Ab.
G = Green time, R = Red time, A = Amber time

24. The actual green time needed is increased in
proportion to the ratio of approach volumes
of two roads in veh/hr/lane, with higher traffic
4. Ga/Gb = na/nb
na & nb approach(traffic) volume during peak hr
5. Ga’ & Gb’ is modified green time obtained.
6. C = Ga’ + Gb’+ Aa +Ab
C =cycle length
7. Do not walk period DWa = Rb, DWb = Ra
8.Walk time = C – (Dwa + C.Ia)
= C - (DWb + C.Ib)

25. Webster method
Ga = ya/Y(Co – L), Gb = yb/Y(Co – L)
Co =( 1.5L + 5)/(1-Y)
Y= ya + yb
ya = qa/Sa, yb = qb/ Sb
L= 2n + R
Where, n = no. of phase
R = all red time & 2 indicates starting delay time lost
qa & qb = normal traffic flow in road a and b
Sa & Sb = saturation traffic flow in road a and b

26. IRC METHOD
It is the combination of approximate and webster
method.
By approximate method find cycle length’
Check for clearing the vehicle arrival during green
phase.
Ga = 1*6sec. + (Xa - 1) 2sec. By IRC method
Gb = 1*6sec. + (Xb- 1) 2 sec.
Xa & Xb = na/C, nb/C respectively.
na& nb approaching traffic volume and C is the cycle
length.
Ga & Gb of IRC method should not be greater then Ga
& Gb of approximate method.
Check for optimum signal cycle length by webster
method

27. Traffic signs
1. Regulatory sign (stop, one wat sign, speed
limit width limit etc.)
2. Warning sign (right hand curve, left hand
curve, typical cautionary sign etc.)
3. Informatory sign (road junction approach,
route marker sign)
4. Compulsory direction control sign (
compulsory turn left, compulsory turn ahead
etc)

28. Design of parking
A) Parallel parking: N = L/6.6
B) Angle parking:
30 degree , N = (L- 0.85)/5.1
45 degree, N = (L-2)/3.6
60 degree, N= (L-2)/2.9
90 degree, N= L/2.5
Where , N = no. of spaces b/w the vehicle
L= length of vehicle