1. What are the objectives objectives of traffic traffic volume volume count? And discuss discuss various various traffic traffic studies studies
Traffic Traffic volume count is the method in which the amount and direction of movement of traffic is obtained by different methods a. Manu Manual al metho ethods ds b. Combination of manual and mechanical methods c. Auto Automa mati ticc devi device cess The various objective of conduction a volume count is as follows 1. 2. 3. ". #. $. %.
Planni Planning ng of highway highway activi activitie tiess Measur Measureme ement nt of curren currentt demand demand valuat valuation ion of of e!isti e!isting ng traff traffic ic flow flow Planni Planning ng of highway highway activi activitie tiess Measur Measureme ement nt of curren currentt demand demand valuat valuation ion of of e!isti e!isting ng traff traffic ic flow flow &esign &esign of the geomet geometric ric characte characteri risti stics cs of a highwa highway y' for e!am(le' e!am(le' number of lanes' lanes' intersection signali)ation' or channeli)ation *. Ca(a Ca(aci city ty anal analy ysis sis +. &evelo &evelo(men (mentt of (rograms (rograms related related to traffic traffic o(eration o(erations' s' for e!am(le e!am(le'' one,way one,way street street systems or traffic routing 1-. &esi &esign gn of geom geomet etri ricc char charact acter eris isti tics cs'' with with (art (artic icul ular ar refe refere rence nce to turn turnin ing, g,ra radi diii reuirements' ma!imum grades' lane widths' and so forth 11. &evelo(ment of im(rovement and maintenance (rograms 12. &evelo(ment of freeway and major arterial arterial street systems systems 13. valuation of the economic feasibility feasibility of highway (rojects
Importance of Traffic Volume Study: Traffic survey is very im(ortant to be (erformed because it can 1. /ncrea /ncrease se the the effici efficiency ency and and life life of road roadss 2. 0educes 0educes traf traffi ficc volume volume at a (articu (articular lar secti section on 3. Provide Provide better better means means for develo(m develo(ment ent of infrastru infrastructures ctures ". Provide Provide better means means to utili)e utili)e other other roads roads in case case of s(ecial s(ecial events events in the city city #. Provide Provide estimat estimatee of no vehicles vehicles against against no of (ersons (ersons Ty(es of volume studies Traffic volume studies
/m(ortance 1. Planning 2. Traffic o(eration and
Presentation of data •
Annual average daily traffic
control 3. Traffic (attern ". tructura ural design of (avements #. 0egulatory ory measures
(eed studies
4rigin and destination studies
(eed and delay studies
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Average daily traffic Trend chart ariation chart Traf Traffi ficc flow flow ma(s ighest hourly volume Average s(eed of vehicle Cumulative s(eed Modal average
1. &esign • various geometric elements • 2. To conduct before and • after studies 3. Traffic ca(acity ". Accident studies #. Planning traffic control and regulation $. (eed tr trends 1. Plan th t he ro r oad &esire lines netw networ or5 5 and and other faci facili liti ties es for for vehicular traffic 2. Plan and sched chedul ulee of different modes of trans(ortation for tri( demand 1. To assess 0unning • before and s(eed after studies 4verall • 2. Traffic s(eed
ca(acity
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Traffic ca(acity study
Par5ing study
6luctuations in s(eed &elay between two stations
1. 7efore and PC89hr after studies 2. 1. Par5ing Par5ing • demand accumulatio 2. Par5ing n characteristic Par5ing • s duration 3. Par5ing s(ace Par5ing • inventory inde! Par5ing • volume •
Accident study
1. To study the cause of accident 2. To evaluate e!isting design 3. To carry out before and after studies ".
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Condition diagram Collision diagram
. Write a note on thirtieth hi!hest hourly volume
The general unit of measuring traffic on highway is annual average daily traffic volume' abbreviated as AA&T. /t is eual to the total annual volume of traffic divided by the number of days in an year. A 5nowledge of traffic in terms of AA&T is not of much use in geometric design' since it does not re(resent the variation in traffic during months of an year' days of the wee5' hours of a day. o commonly used unit for geometric design is the 3-th highest hourly volume.
The 3-th highest hourly volume is defined as the volume which is e!ceeded only 2+ times in a year and all other hourly volumes of the year will be less than this value. This value is generally ta5en as the hourly volume for the design and will ensure tha t there will be congestion only during 2+ hours in a year.
". #efine $%&. 'ist and e(plain the characteristics. Also mention recommended I)% values of $%&
The PC8 may be considered as a measure of relative s(ace reuired for a vehicle class com(ared to that of a (assenger car under a s(ecified set of roadway' traffic and other conditions. The PC8 value of the vehicle class may be considered as the ratio of the ca(acity of a roadway when there are (assenger cars only to the ca(acity of the same roadway when there are vehicles of that class only.
*actors affectin! $%& values
The PC8 values of different vehicle classes de(end u (on several factors. ome of these are listed below. 1. ehicles characteristics such as dimensions' (ower' s(eed' acceleration and brac5ing characteristics 2. Transverse and longitudinal ga(s or clearances between moving vehicles which de(ends u(on the s(eeds' driver characteristics and the vehicle clasees at the adjoining s(aces.
3. Traffic stream characteristics such as com(osition of different vehicle classes' mean s(eed and s(eed distribution of the mi!ed traffic stream' volume to ca(acity ratio ". 0oadway characteristics such as road geometrics including gradient' curve' etc. access controls' rural or urban road' (resence of intersections and the ty(es of intersections #. 0egulation and control of traffic such as s(eed limits' one way traffic' (resence of different traffic control devices $. nvironmental and climatic conditions
*actors to be considered in the analysis of $%&
1. Average s(eed of the vehicle class under the (revailing roadway and traffic conditions within the desired s(eed ranges 2. Average length and width of the vehicles 3. Average transverse and longitudinal ga( between the vehicles of the same class Type of vehicle two wheelers Car Auto 7us ' truc5 :C Tractor with trailor and cart orse cart 7ulloc5 cart
$%& values -.# 1 1 3 1.# ".# 3 " *
+. With a neat s,etch e(plain the concept of ori!in and destination survey -bjectives of conductin! -ri!in and destination studies • • •
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Plan the road networ5 and other facilities for vehicular traffic Plan the schedule of different modes of trans(ortation 4& gives information about actual direction of travel' selection of routes and length of tri(s To judge the adeuacy of e!isting routes To identify the location suitable for e!(ressways
Travel surveys are conducted to establish a com(lete understanding of the travel (atterns within the study area. 6or single (rojects ;such as a highway (roject<' it may be sufficient to use traffic counts on e!isting roads or ;for transit< counts of (assengers riding the (resent system. owever' to understand why (eo(le travel and where they wish to go' origin,destination ;4,&< survey data can be useful. The 4,& survey as5s uestions about each tri( that is made on a s(ecific day=such as where the tri( begins and ends' the (ur(ose of the tri(' the time of day' and the vehicle involved ;auto or transit<=and about the (erson ma5ing the tri(=age' se!' income' vehicle owner' and so on. The 4,& survey may be com(leted as a home interview' or (eo(le may be as5ed uestions while riding the bus or when sto((ed at a roadside interview station. ometimes' the information is reuested by tele(hone or by return (ostcard. 4,& surveys are rarely com(leted in communities where these data have been (reviously collected. 4,& data are com(ared with other sources to ensure the accuracy and consis tency of the results. Among the com(arisons used are crosschec5s between the number of dwelling units or the tri(s (er dwelling unit observed in the survey with (ublished data. creenline chec5s can be made to com(are the number of re(orted tri(s that cross a defined boundary' such as a bridge or two (arts of a city' with the number actually observed. /t is also (ossible to assign tri(s to the e!isting networ5 to com(are how well the data re(licate actual travel. /f the screenline crossings are significantly different from those (roduced by the data' it is (ossible to ma5e adjustments in the 4,& results so that conformance with the actual conditions is assured. &ifferent methods used to obtain 4 and & data are 1. 0oadside interview 2. :icense (late 3. Tag on car method ". Post card method #. ome interview method #ifferent ays of representin! the results of ori!in and destination studies are listed belo 1. 2. 3. ".
4rigin and destination tables showing number of tri(s between different )ones &esire lines Pie charts Contour lines
#esire line
&esire line is the gra(hical re(resentation of the data co llected from origin and destination survey' where in the location will be identified and lines are drawn connecting d ifferent locations the thic5ness of the line re(resents the number of tri(s occurring between the two locations. /f the variation in the data is very small then we can also write numbers on to( of the lines connecting two (oints. >here the line re(resents the travel occurring between the locations and number re(resents the freuency.
/. With the help of s,etches briefly e(plain on street par,in! -n0Street $ar,in! *acilities These are also 5nown as curb facilities. Par5ing bays are (rovided alongside the curb on one or both sides of the street. These bays can be unrestricted (ar5ing facilities if the duration of (ar5ing is unlimited and (ar5ing is free' or they can be restricted (ar5ing facilities if (ar5ing is limited to s(ecific times of the day for a ma!imum duration. Par5ing at restricted facilities may or may not be free. 0estricted facilities also may be (rovided for s(ecific (ur(oses' such as to (rovide handica((ed (ar5ing or as bus sto(s or loading bays. Common methods of on,street (ar5ing 1. Parallel (ar5ing 2. 3-? angle (ar5ing 3. "#? angle (ar5ing ". $-? angle (ar5ing #. 0ight angle (ar5ing Parallel (ar5ing consumes the ma!imum curb length which decreases as the angle of (ar5ing increases. The minimum curb length is consumed by the right angle (ar5ing' which accommodates nearly 2 times the number of vehicles as (arallel (ar5ing 4n the other hand' (arallel (ar5ing ma5es the least use of the width of the street and this is an im(ortant consideration in narrow streets. As the (ar5ing angle increases the width of street used also increases 6rom the (oint of view of manoeuvrability' angle (ar5ing seems to be better than (arallel (ar5ing which usually involves a bac5ing motion. &elay to traffic is minimum with angle (ar5ing As regards safety' it has been noticed that angle (ar5ing is more ha)ardous than (arallel (ar5ing
$. &efine. a. 7asic ca(acity b. Practice ca(acity c. Possible ca(acity Basic capacity is the ma!imum number of vehicles;PC8< that can ( ass a given (oint on a lane or roadway during one hour under the most nearly ideal roadway and traffic conditions which can (ossibly be attained. Two roads have same (hysical features will have same basic ca(acities irres(ective of the traffic conditions. Possible Capacity is the ma!imum number of vehicles which can (ass a given (oint on a lane or highway during one hour under the (revailing roadway and traffic conditions. This means that the (ossible ca(acity of a highway will always be lower than the basic ca(acity unless the (revailing conditions of the traffic' a((roach the ideal conditions. Therefore the (ossible ca(acity may vary from - to the ma!imum' i.e.' 7asic ca(acity. Practical Capacity is the ma!imum number of vehicle that can (ass a given (oint on a lane or roadway during one hour' without traffic density being so great as to cause unreasonable delay' ha)ard or restriction to the driver@s freedom to man,oeuvre under the (revailing roadway and traffic conditions
. 2riefly e(plain procedure adopted in floatin! car method and analysis of data collected and representation of results Moving-Vehicle Technique. /n this method' the s(eed and flow can be obtained by travelling in a car against and with the flow' and noting down the journey time' the number of vehicles met with from the o((osite direction' and number of vehicles overta5ing the test vehicle and number of vehicles overta5en by the test vehicle A small' (referably even' number of test cars is reuired,usually two,each car carrying a driver and three observers. 4ne observer in the car counts o((osing traffic' using hand tallies. Another observer carries a recording board on which a watch is mounted. The recording board carries a journey log (re(ared in advance' on which the observer records the totals from the hand tallies and times at (redermined (oints en,route' together with the times of sto((ing and starting at intersection. /t is desirable to have two sto( watches' one for recording the continuous time as the observer o(erates buttons. A third observer records the number of overta5ing and overta5en vehicles' and if reuired' the number of (ar5ed vehicles. /f only two observers are available' the driver is instructed to overta5e as many vehicles as overta5en by him. The method is well suited to study the s(eeds along different roads in a area. ince conditions may vary from section to section on the route' the route is divided into convenient sections' say -.%#,1.# 5m in lengthB it is desirable to have the ends of these sections at major intersections so that large discontinuities in s(eed and flow do not o ccur inside the section.
/t is desirable that twelve to si!teen runs in each direction along the route be made and the results averaged out so as to arrive at an accurate estimate of the s(eed and flow. Advantages of the method 1. The method gives an unbiased estimate of flow. 0andom errors can' however' occur due to observers errors and random fluctuations in flow' but these are not serious under normal conditions. 2. As com(ared to the stationary observer method' the moving observer method is euivalent to a stationary count over twice the single journey time. ence it is economical in man(ower. 3. /t enables data on s(eed and flow to be collected at the same time. This is (articularly advantageous when analysing the relations between the two. ". /t gives mean values of flow and s(eed over a section. 0ather than at a (oint. Thus it gives directly the s(ace mean s(eed' whereas s(ot s(eed studies gives the time measn s(eed. #. /t gives additional information on sto(s at intersections' delays' (ar5ed vehicles etc. Analysis of the data
6low !sDyn9 ;tsDtn< volume along the direction of flow
!s volume of traffic in PC8 moving in the o((osite direction ynoverta5ing vehicles minus over ta5en vehicles ts time reuired when moving in o((osite to the flow tn time reuired when moving along the flow Time;Eourney time<
tntn, yn9n 0e(resentation of results 1. Eourney time 2. Eourney s(eed 3. 0unning time ". 0unning s(eed #. Traffic flow in PC89hr
*. >rite a. b. c.
a note of Condition diagram Collision diagram 4ff street (ar5ing
Collision Diagrams A collision diagram is a schematic re(resentation of all accidents occurring at a given location over a s(ecified (eriod. &e(ending u(on the accident freuency' the Fs(ecified (eriodG usually ranges from one to three years. ach collision is re(resented by a set of arrows' one for each vehicle involved' which schematically re(resents the ty(e of accident and directions of all vehicles. Arrows are generally labelled with codes indicating vehicle ty(es' date and time of accident' and weather
conditions. The arrows are (laced on a schematic ;not,to scale< drawing of the intersection with no interior details shown. 4ne set of arrows re(resents one accident. /t should be noted that arrows are not necessarily (laced at the e!act s(ot of the accident on the drawing. There could be several accidents that occurred at the same s(ot' but se(arate sets of arrows would be needed to de(ict them. Arrows illustrate the occurrence of the accident' and are (laced as close to the actual s(ot of the accident as (ossible. 6igure shows the standard symbols and codes used in the (re(aration of a ty(ical collision diagram. 6igure shows an illustrative collision diagram for an intersection. The collision diagram (rovides a (owerful visual record of accident occurrence over a significant (eriod of time. /n 6igure it is clear that the intersection has e!(erienced (rimarily rear,end and right,angle collisions' with several injuries but no fatalities during the study (eriod. Many of the accidents a((ear to be clustered at night. The diagram clearly (oints out these (atterns' which now must be correlated to the (hysical and control characteristics of the site to determine contributing causes and a((ro(riate corrective measures. +.
/llustration of the collision diagram
Condition Diagrams A condition diagram describes all (hysical and environmental' conditions at the accident site. The diagram must show all geometric features of the site' the location and descri(tion of all control devices ;signs' signals' mar5ings' lighting' etc.<' and all relevant features of the roadside environment' such as the location of driveways' roadside objects' land uses' etc. The diagram must encom(ass a large enough area around the location to include all (otentially relevant features. This may range from several hundred feet on intersection a((roaches to .2#,.#- mile on rural highway sections. 6igure illustrates a condition diagram. /t is for the same site and time (eriod as the collision diagram of 6igure. The diagram includes several hundred feet of each a((roach and shows all driveway locations and the commercial land uses they serve. Control details include signal locations and timing' location of all sto( lines and crosswal5s' and even the
location of roadside trees' which could conceivably affect visibility of the signals.
-ff0Street $ar,in! *acilities These facilities may be (rivately or (ublicly ownedH they include surface lots and garages. elf, (ar5ing garages reuire that drivers (ar5 their own automobilesH attendant,(ar5ing garages maintain (ersonnel to (ar5 the automobiles. The ty(es of off,street facilities commonly considered are 1. surface car (ar5s 2. multi,storey car (ar5s 3. roof (ar5s ". mechanical car (ar5s #. underground car (ar5s There are some basic considerations which govern the location of these facilities. ince thse facilities are costly to (rovide and maintain' a com(rehensive study should be done before hand to hel( determine the location' ty(es and si)e of these facilities. 13. Write a note on a. $ar,in! accumulation b. $ar,in! inde( c. $ar,in! turnover d. $ar,in! volume e. Space hour f. 'evel of service 1. A space0hour is a unit of (ar5ing that defines the use of a single (ar5ing s(ace for a (eriod of 1 hour.
. $ar,in! volume is the total number of vehicles that (ar5 in a study area during a s(ecific length of time' usually a day. ". $ar,in! accumulation is the number of (ar5ed vehicles in a study area at any s(ecified time. These data can be (lotted as a curve of (ar5ing accumulation against time' which shows the variation of the (ar5ing accumulation during the day. +. The par,in! load is the area under the accumulation curve between two s(ecific times. /t is usually given as the number of s(ace,hours used during the s(ecified (eriod of time. /. $ar,in! duration is the length of time a vehicle is (ar5ed at a (ar5ing bay. >hen the (ar5ing duration is given as an average' it gives an indication of how freuently a (ar5ing s(ace becomes available. 4. $ar,in! turnover is the rate of use of a (ar5ing s(ace. /t is obtained by dividing the (ar5ing volume for a s(ecified (eriod by the number of (ar5ing s(aces. %. 'evel of service: Level of service (LOS) is a qualitative measure used to relate the quality of trac service. LOS is used to analyze highways by categorizing trac ow and assigning quality levels of trac based on erformance measure li!e seed" density"etc 11. #efine the term spot speed study. 5(plain the presentation of spot speed data Spot speed is the instantaneous speed of a vehicle at a s(ecified location. Spot speed can be used to design the geometry of road li5e hori)ontal and vertical curves' su(er elevation etc. The methods used for conducting s(ot s(eed studies can be grou(ed as underB 1. Those that reuire observation of time ta5en by a vehicle to cover a 5nown distance. 2. 0adar s(eedometer which automatically records the instantaneous s(eed. 3. Photogra(hic method 6irst method can be further subdivided as 1. those in which vehicles are timed over a long distance 2. Those in which vehicles are timed over a short distance The long base methods commonly used are. 1. &irect timing (rocedure. 2. nosco(e 3. Pressure contact tubes )ecommended base len!th The following base length for the long,base methods are ado(ted Avg. (eed of Traffic tream 7ase length :ess than "2% "-,$# #" Ireater than $# *1 #irect timin! procedure for spot speed determination This is one of the sim(lest methods for s(ot s(eed determination. Two reference (oints are mar5ed on the (avement at a suitable distance a(art and an observer starts and sto(s and accurate sto( watch as a vehicle crosses these two mar5s. 6rom the 5nown distance and the measured time intervals s(eeds are calculated. 5illed observers can read a sto(,watch to an accuracy of -.2 sec. if the observer stations himself incons(icuously' the s(eed readings are not influenced by driver reaction. The disadvantage with this method is that large errors are li5ely to be introduced because of the (aralla! effect.
A sim(le variation of this method is to station two observers one at each reference (oint. The observer standing at the reference (oint which the vehicles (ass first' signals that a vehicle to be timed is (assing the the (oint and the second observer then starts a sto(watch. The second observer sto(s the sto( watch when he observes the same vehicle (assing the reference (oint. The disadvantage with this method is that it involves the reaction time of two individual observers. 5noscope A sim(le device called nosco(e eliminates the (aralla! effect that cree(s in when the direct readings are ta5en by one observer. This device' also 5nown as the mirror,bo! is an :,sha(ed bo!' o(en at both ends' with a mirror set at a "#,degree angle to the arms of the instrument. The instrument bends the line of sight of the observer so that it is (er(endicular to the (ath of the vehicle. The method can be used with one enosco(e or with two enosco(es. /f one enosco(e is used' the instrument is (laced directly o((osite to the first reference (oint and the observer stations himself at the other reference (oint' The sto(,watch is started as soon as the vehicle (asses the first reference (oint and is to((ed as soon as it (asses the observer. /f two enosco(es are used' the observer stations himself mid,way between the two reference (oints and starts the sto(, watch as soon as a vehicle crosses the second reference (oint
$neumatic road tubes6 $ressure tubes Are laid across the lane in which data are to be collected. >hen a moving vehicle (asses over the tube' an air im(ulse is transmitted through the tube to the counter. >hen used for s(eed measurements' two tubes are (laced across the lane' usually about $ ft a(art. An im(ulse is recorded when the front wheels of a moving vehicle (ass over the first tubeH shortly afterward a second im(ulse is recorded when the front wheels (ass over the second tube. The time ela(sed between the two im(ulses and the distance between the tubes are used to com(ute the s(eed of the vehicle. An inductive loop is a rectangular wire loo( buried under the roadway surface. /t usually serves as the detector of a resonant circuit. /t o(erates on the (rinci(le that a disturbance in the electrical field is created when a motor vehicle (asses across it. This causes a change in (otential that is am(lified' resulting in an im(ulse being sent to the co unter. )adar02ased Traffic Sensors 0adar,based traffic sensors wor5 on the (rinci(le that when a signal is transmitted onto a moving vehicle' the change in freuency between the transmitted signal and the reflected signal is (ro(ortional to the s(eed of the moving vehicle. The difference between the freuency of the transmitted signal and that of the reflected signal is measured by the eui(ment and then converted to s(eed in mi9h. /n setting u( the eui(ment' care must be ta5en to reduce the angle
between the direction of the moving vehicle and the line joining the centre of the transmitter and the vehicle. The value of the s(eed recorded de(ends on that angle. /f the angle is not )ero' an error related to the cosine of that angle is introduced' resulting in a lower s(eed than that which would have been recorded if the angle had been )ero. owever' this error is not very large' because the cosines of small angles are not much less than one. o' The s(eed meter is so 5e(t that the angle between the direction of travel of the vehicle and the a!is of transmitted radio wave is as low as (ossible' say 2- degrees. The advantage of this method is that because (neumatic tubes are not used' if the eui(ment can be located at an incons(icuous (osition' the influence on driver behaviour is considerably reduced. 5lectronic0$rinciple #etectors /n this method' the (resence of vehicles is detected through electronic means' and information on these vehicles is obtained' from which traffic characteristics' such as s(eed' volume' ueues' and headways are com(uted. The great advantage of this method over the use of road detectors is that it is not necessary to (hysically install loo(s or any other ty(e of detector on the road. A technology using electronics is video image (rocessing' sometimes referred to as a machine, vision system. This system consists of an electronic camera overloo5ing a large section of the roadway and a micro(rocessor. The electronic camera receives the images from the roadH the micro(rocessor determines the vehicles (resence or (assage. This information is then used to determine the traffic characteristics in real time. 4ne such system is the autoscope. $hoto!raphic method and video camera method Time,la(se camera (hotogra(hy has been used successfully to determine the s(eed of vehicle accurately in crowded streets. According to this method' (hotogra(hs are ta5en at fi!ed intervals of time ;say one sec (er frame< on a s(ecial camera. 7y (rojecting the film on a screen' the (assage of any vehicle can be traced with reference to time. /mages by video ca meras can also be used. 1. 7ention the various methods of carryin! out speed and delay study. 5(plain any to of them
everal methods have been used to conduct travel time and delay studies. These methods can be grou(ed into two general categoriesB ;1< those using a test vehicle and ;2< those not reuiring a test vehicle. The (articular techniue used for any s(ecific study de(ends on the reason for conducting the study and the available (ersonnel and eui(ment. 7ethods )e8uirin! a Test Vehicle This category involves three (ossible techniuesB floating,car' average,s(eed' and moving, vehicle techniues. Moving-Vehicle Technique. /n this method' the s(eed and flow can be obtained by travelling in a car against and with the flow' and noting down the journey time' the number of vehicles met with from the o((osite direction' and number of vehicles overta5ing the test vehicle and number of vehicles overta5en by the test vehicle
A small' (referably even' number of test cars is reuired,usually two,each car carrying a driver and three observers. 4ne observer in the car counts o((osing traffic' using hand tallies. Another observer carries a recording board on which a watch is mounted. The recording board carries a journey log (re(ared in advance' on which the observer records the totals from the hand tallies and times at (redermined (oints en,route' together with the times of sto((ing and starting at intersection. /t is desirable to have two sto( watches' one for recording the continuous time as the observer o(erates buttons. A third observer records the number of overta5ing and overta5en vehicles' and if reuired' the number of (ar5ed vehicles. /f only two observers are available' the driver is instructed to overta5e as many vehicles as overta5en by him. The method is well suited to study the s(eeds along different roads in a area. ince conditions may vary from section to section on the route' the route is divided into convenient sections' say -.%#,1.# 5m in lengthB it is desirable to have the ends of these sections at major intersections so that large discontinuities in s(eed and flow do not o ccur inside the section. /t is desirable that twelve to si!teen runs in each direction along the route be made and the results averaged out so as to arrive at an accurate estimate of the s(eed and flow. Advantages of the method 1. The method gives an unbiased estimate of flow. 0andom errors can' however' occur due to observers errors and random fluctuations in flow' but these are not serious under normal conditions. 2. As com(ared to the stationary observer method' the moving observer method is euivalent to a stationary count over twice the single journey time. ence it is economical in man(ower. 3. /t enables data on s(eed and flow to be collected at the same time. This is (articularly advantageous when analysing the relations between the two. ". /t gives mean values of flow and s(eed over a section. 0ather than at a (oint. Thus it gives directly the s(ace mean s(eed' whereas s(ot s(eed studies gives the time measn s(eed. #. /t gives additional information on sto(s at intersections' delays' (ar5ed vehicles etc.
7ethods 9ot )e8uirin! a Test Vehicle This category includes the license,(late method and the interview method. License-Plate Observations. The license,(late method reuires that observers be (ositioned at the beginning and end of the test section. 4bservers also can be (ositioned at other locations if ela(sed times to those locations are reuired. ach observer records the last three or four digits of the license (late of each car that (asses' together with the time at which the car (asses. The reduction of the data is accom(lished in the office by matching the times of arrival at the beginning and end of the test section for each license (late recorded. The difference between these times is the travelling time of each vehicle. The average of these is the average travelling time on the test section. /t has been suggested that a sam(le si)e of #- matched license (lates will give reasonably accurate results. The section can be divided into stretches of -.# to 1.-- 5m length. The accuracy of the data collected from this method is about D+*,++J. Two observers can record the data at the rate of about 3-- vehicles (er hour.
The advantages of this method is that no so(histicated instruments are needed e!ce(t sto( watches. The analysis is how,ever' laborious and time consuming' but can be rendered easily with the hel( of com(uters. The method can only be used on highway sections having minor or no intersections' since the vehicles may enter' leave or sto( within the section having intersections. ence this method is suitable for rural roads. 5levated observer method /n this method' the observer stationed on to( of the elevated building select vehicles at random and follow their course along the road' noting the time of entering the section' duration and nature of delays suffered and the time of leaving. The test section has to be short' such as a street in central area of a city. Interviews. The interviewing method is carried out by obtaining information from (eo(le on the study site regarding their travel times' their e!(erience of delays' and so forth. who drive This method facilitates the collection of a large amount of data in a relatively short time. owever' it reuires the coo(eration of the (eo(le contacted' since the result de(ends entirely on the information given by them. 1". 7ention the objectives of accident studies. Also mention the various causes of accidents -bjectives 1. To identify causes and suggest remedial measures at blac5 s(ots ; where accidents are freuented< 2. valuate the e!isting system and (ro(osed redesign or new design to im(rove road safety 3. Carry out 7efore and after studies for analysis and assessing the change in system ". >or5out accident cost';direct and indirect< and financial losses #. conomic justification for the im(roved (ro(osals. $. To wor5out benefit cost ratio %auses 0oad' vehicle' driver and environment are the main causes in which (edestrians' road users; violation of rules' carelessness of movement<' and (assengers;alighting and boarding moving vehicles<' animals' and other; sign' signals' badly located advance boards etc< #river The human causes attribute to about $-,*#J accidents. The following are some of the reasons. 1. !cessive or very low s(eeds 2. 6ollowing too closely behind another vehicle 3. Kot 5ee(ing to the left while driving ". 6ailure to 5ee( lanes and ha(ha)ard crossing of lanes #. 6ailure to give signals for sto(' turn and overta5e vehicles. $. 4verta5ing dangerously %. /gnoring traffic lights and signals *. Moving against one way +. &riving under influence
1-. /m(atience to traffic 11. &istraction' conservation while driving' loud music while driving etc 12. 8se of cell (hone while driving 13. &riving a two wheeler without a helmet 1". Poor vision and lac5 of hearing Vehicles 1. 7ra5e failure' headlights' taillight' (ar5ing light and indicators not in order 2. 7ald and (oorly inflated tires' inadeuate fuel' bra5e oil' fuel oil 3. /neffective steering' non adjusted rear view mirror ". Carrying more (assengers than recommended #. !ceeding in length' height width than (rescribed $. !ceeding the legal a!le weight %. 2 wheeler without sari gaurds *. Kot using seat belts +. 7ad wor5ing condition of wi(er 1-. &ar5 sunfilm of glasses 11. Public vehicles without white reflector at front. 12. Ias cylinders not (ro(erly secured )oad 1. Poorly designed and maintained roads 2. Poor visibility 3. Poorly illuminated roads ". /m(ro(er and insufficient road geometrics #. /nadeuate road signs and im(ro(er location $. 6aulty design' im(ro(er location and not (ro(erly (ainted and illuminated s(eed brea5ers. %. /m(ro(er medians and 5erbs *. Pot holes and man holes +. 4il s(illed road surface 1-. 0oad side low level tree branches 11. 7ottle nec5 along the roads 12. Iradients of roads 13. /nadeuate road width nvironment !cessive wind' time of the day' fog' landslides and rain may be some of the causes
1+. #efine a. )unnin! speed b. Space0mean speed c. Time mean speed d. #elay
0unning s(eed is the average s(eed maintained by a vehicle over given course while the vehicle is in motion. /t is significant to note the clause' while the vehicle is in motion. 7ecause the
running s(eed is obtained by dividing the length of course by the time the vehicle is in motion' i.e. by the running time' which e!cludes that (art of the journey time when the vehicle suffers delay. Thus' 0unning s(eedlength of course 0unning time length of course Eourney time, delay Eourney s(eed' also 5nown as overall travel s(eed' is the effective s(eed of a vehicle between two (oints' and is the distance between two (oints divided by the total time ta5en by the vehicle to com(lete the journey' including all delays incurred en,route. ThusB Eourney s(eed distance . Total journey time ;including delays< Time,mean s(eed is the average s(eed measurement at one (oint in s(ace over a (eriod of the time. /t is the average of a number of s(ot s(eed measurements (ace,mean s(eed is the average of the s(eed measurements at an instance of time over a s(ace. &elayB it is the amount of time during which the vehicle is forced to sto( because of traffic congestion' accident etc 1#. numerate the different methods of traffic volume studies 7ethods of volume count The methods available for conduction traffic counts are listed below 1. Manual methods 2. Combination of manual and mechanical methods 3. Automatic devices Manual methods use field (ersonnel to count and classify traffic flowing (ast a fi!ed (oint. Automatic devices enable a count of traffic to be ta5en at any given location and a record to be 5e(t of the count. 9umber of observers The number of observers needed to count the vehicles de(ends u(on the number of lanes in the highway on which the count is to be ta5en and the ty(e of information desired. The indications are given in the table below )oad *eatures and countin! re8uirements 9o of vehicles per hour that can be counted by one trained observer 2,:ane tow,way road' with se(arate #-- vehicles (er hour in one direction observers for each directionB vehicles to be counted and classified 2 lane two,way road' with one observer for 2-- vehicles (er hour in both directions both directionsB vehicles to be counted and classified for each direction se(eratly 2 lane two,way road' with one observer for *-- vehicles (er hour both direction both directionsB vehicles to be sim(ly counted with no reuirement for
classification direction
and
(osting
into
se(arate
58uipments needed The following eui(ments are needed 1. A watch 2. Pencils' eraser and (encil shar(ener 3. u((ly of blan5 field data sheets ". Cli( board 7ethodolo!y Manual counting involves one or more (ersons recording observed vehicles using a counter. >ith this ty(e of counter' both the turning movements at the intersection and the ty(es of vehicles can be recorded. Kote that in general' the inclusion of (ic5u(s and light truc5s with four tires in the category of (assenger cars does not create any significant deficiencies in the data collected' since the (erformance characteristics of these vehicles are similar to those of (assenger cars. /n some instances' however' a more detailed brea5down of commercial vehicles may be reuired which would necessitate the collection of data according to number of a!les and9or weight. owever' the degree of truc5 classification usually de(ends on the antici(ated use of the data collected. Traffic flowing (ast a survey (oint is counted by an observer' who would record the flow using either a tally counter or by ta5ing a manual count of vehicles and recording it on (a(er' ty(ically using a five bar gate counting techniue' or by using a hand,held com(uter. Counts are classified' to identify the volume and mi! of ty(es of vehicles using the road at the survey (oint. owever' the level of classification used will very much de(end u(on the needs of the survey. 6or e!am(le' it may be adeuate to use a sim(ler form of classification' such as cars and ta!is' buses and commercial vehicles. The engineer should choose an a((ro(riate level of classification for each study. /f a data collection survey is only (lanned to cover a short (eriod of time' then the e!(ense of installing an automatic counter may not be justified when com(ared with the cost of using a surveyor. The surveyor also has the ability to discriminate between classes of vehicles. Manual counts generally offer better value for money when data is to reuired for a single day or for less than the full 2",hour day but collected over 2 or 3 days. Manual classified counts;MCCs< become more difficult where flows are very high' and where any brea5 in concentration can introduce high error rates in the count. /f the engineer wishes to gain a uic5 insight to traffic conditions over a wider are a' short (eriod' sam(le traffic counts can be ta5en over a wide area and factored u(' to re(resent the hourly flow. Thus' for e!am(le' if one wished to have an understanding of traffic levels at a com(le! junction' traffic could be counted at each arm for #L1- minutes and then factored u( to hourly counts' to give an understanding of conditions. This is a good method of gaining a uic5 insight into traffic levels but should not be used as a substitute for a (ro(erly organised traffic survey.
The Advantages of manual methods and situations where these are to be (referred areB 1. &etails such as vehicle classification and number of occu(ants can be easily obtained. >ith automatic devices these data are unfortunately lac5ing' and hence automatic counting should be su((orted by manual counts. 2. The data can be collected giving the brec5down of traffic in each direction of travel 3. (ecific vehicular movements such as left,turns' right,turns' straight, aheads etc. at a junction can be noted and recorded.
". Manual methods enable any unusual conditions obtaining at the time of count to be recorded. This will hel( in understanding and analysing the traffic characteristics. uch' unusual conditions can be adverse weather conditions' traffic brec5downs' tem(orary closure of any lane of the highway for maintenance o(erations etc. #. /n develo(ing countries' so(histicated automatic devices are not indigenously (roduced. 4n the other hand' man(ower for counting is available com(aratively chea(ly $. Pilferage and vandalism often (revent the use of costly eui(ments in remote rural areas' and in such cases manual methods are the only solution %. ven if automatic devices are used' it is often necessary to chec5 the accuracy of these devices (eriodically and manual methods serve this (ur(ose *. &ata accumulated by manual methods are easy to analyse +. Manual methods are suitable for short,term and non continuous counts. The main disadvantages of the manual count method are that ;1< it is labour intensive and therefore can be e!(ensive' ;2< it is subject to the limitations of human factors' and ;3< it cannot be used for long (eriods of counting. %ombination of manual and mechanical method An e!am(le of a combination of manual and mechanical methods is the multi(le (en recorders. A chart moves continuously at the s(eed of a cloc5. &ifferent (ens record the occurrence of different events on the chart. The actuation of the event recorder (en is by (ressing the electric switch associated with each (en recorder. 6or instance' a (articular switch may be (ressed whenever a (articular class of vehicles arrives and this o(erates the (er on the channel which can be identified with the arrival of a (articular class of vehicle. The advantages of this method are 1. A (ermanent record is 5e(t of the arrival of each class of vehicle. The classification and vehicle count are (erformed simultaneously 2. Additional information such as time,headway between successive vehicles and the arrivals (er unit time become available Automatic #evices Sensors ensors o(erated on several different (rinci(les are available 1. $neumatic tubeB a fle!ible tube with one end sealed is clam(ed to the road surface at right angles to the (avement. The other end of the tube is connected to a dia(hragm actuated switch. >hen an a!le of a vehicle crosses the tube' a volume of air gets dis(laced thus creating a (ressure which instantaneously closes the electrical contact through the switch. Two such contacts results in one count being registered' thus re(resenting the two a!les in a vehicle. /naccuracies are caused when vehicles with more than two a!les are (resent in the traffic stream in a((reciable number. 7ecause of their sim(licity and their chea(ness' (neumatic tube sensors are very (o(ular. ome difficulty may be caused in fi!ing them to gravel surfaces and they have additional drawbac5 that they are easily (ilfered by vandals. They are li5ely to be damaged by crawler tractors' tyre chains' snow (loughs and similar eui(ments. They cann ot detect vehicles by lanes 2. 5lectric contact B a (air of steel stri(s are contained in a rubber (ad which is buried beneath the surface. 4n being (ressed by the weight of a moving a!le the steel stri(s come into contact with each other and cause the electric current to flow. lectric contact
3.
".
#.
$.
detectors' while retaining the advantages and disadvantages of (neumatic tube detectors' have the ability to detect vehicles in individual lanes %o0a(ial cable: a co,a!ial cable is clam(ed across the road surface' with the ca(ability of generating signals with the (assage of a!les. These signals actuate a transistorised counter. The advantages associated with this ty(e of detectors are their better reliability and (erformance on inferior ty(e of surfaces and their lesser susce(tibility to damage $hoto0electric B on one end of the road is a source of light which emits a beam across the road. At the other end is a (hoto,cell which can distinguish between the light beam and absence of light beam. The (assage of a vehicle in the (ath of the light beam obstructs the beam and causes detection by (hoto,cell. The difficulty with this otherwise sim(le techniue is that obstruction can be caused by (edestrians and that more than one vehicle in the different traffic lanes' but (osition in the line of the beam simultaneously' will register only one vehicle )adarB &o((ler ffect is a well,5nown (henomenon in (hysics which enables detection of vehicles moving at a s(eed. >hen a moving object a((roaches or recedes from the moving object will be different from the freuency of the signal emitted by the source. This difference in the two freuencies causes detection of a moving object. The initial cost of this device is no doubt high' but its accuracy and reliability' a (art from its non, susce(tibility to damage by traffic' have much to a((eal. Infra0red and ultrasonic . /nfrared sensors can detect the heat radiated from a vehicle or can react to the reflection from the vehicle of infra,red radiation emitted by the sensonrs
14. 5(plain different measures throu!h hich accidents can be minimied )emedies To im(rove the safety on the roads we have to follow 3 s engineering' enforcement and education.
5n!ineerin! 6or the roads to be safer we have to first design geometrics of the road along with all other features (ro(erly li5e' road width' lane width' easy gradients' hori)ontal and vertical curves' intersection design ;channeli)ation<' (avement surface characteristics' s5id resistance' service road condition arterial road' one way system' adeuate foot(ath' flyovers' subways' raised 5erbs'.medians with grill' street lighting' s(eed brea5ers' mar5ing' cutting tree branches. 5nforcement &one by enforcement officers, traffic and trans(ort officials to boo5 violators' s(eed controls' radar gun to measure s(eeding and challenging to boo5 drin5 and driving cases' traffic rules' regulations and control' installation of signals' signages and enforcing them' lane disci(line' mar5ings' channali)ination' creation of islands' strict issue of &riving licenses' medical chec5u(s and fitness certificate. 5ducation: This is im(ortant to bring traffic awareness and safety' (edestrian' (assengers and road users to follow ti(s for diffensive driving' education to children through (osters' banners etc' )ebra crossing' (eriodic training to all the road users' by lectures' e!hibition' wor5sho(s etc. 1. 'ist and e(plain different types of volumes counts
&ifferent ty(es of traffic counts are carried out' de(ending on the antici(ated use of the data to be collected. These different ty(es will now be briefly discussed. %ordon and screen0line survey These (rovide useful information about tri(s from and to e!ternal )ones. 6or large study area' internal cordon,line can be needed and surveying can be conducted. The objective of the survey is (rimarily to collect the origin and destination )ones and for this many suitable methods can be ado(ted. /t could be either recording the license (late number at all the e!ternal cordon (oints or by (ost,card method. creen lines divide the study area into large natural )ones' li5e either sides of a river' with few crossing (oints between them. The (rocedure for both cordon,line and screen,line survey are similar to road,side interview. owever' these counts are (rimarily used for calibration and validation of the models. Intersection %ounts /ntersection counts are ta5en to determine vehicle classifications' through movements' and turning movements at intersections. These data are used mainly in determining (hase lengths and cycle times for signali)ed intersections' in the design of channeli)ation at intersections' and in the general design of im(rovements to intersections.
$edestrian Volume %ounts
olume counts of (edestrians are made at locations such as subway stations' midbloc5s' and crosswal5s. The counts are usually ta5en at these locations when the evaluation of e!isting or (ro(osed (edestrian facilities is to be underta5en. uch facilities may include (edestrian over(asses or under(asses. Pedestrian counts can be made using the T&C,12 electronic manual counter described earlier and shown in 6igure ".%. The locations at which (edestrian counts are ta5en also include intersections' along sidewal5s' and mid,bloc5 crossings. These counts can be used for crash analysis' ca(acity analysis' and determining minimum signal timings at signali)ed intersections. $eriodic Volume %ounts /n order to obtain certain traffic volume data' such as AA&T' it is necessary to obtain data continuously. owever' it is not feasible to collect continuous data on all roads because of the cost involved. To ma5e reasonable estimates of annual traffic volume characteristics on an area, wide basis' different ty(es of (eriodic counts' with count durations ranging from 1# minutes to continuous' are conductedH the data from these different (eriodic counts are used to determine values that are then em(loyed in the estimation of annual traffic characteristics. The (eriodic counts usually conducted are continuous' control' or coverage counts. %ontinuous %ounts. These counts are ta5en continuously using mechanical or electronic counters. tations at which continuous counts are ta5en are 5nown as (ermanent count stations. /n selecting (ermanent count stations' the highways within the study area must first be (ro(erly classified. ach class should consist of highway lin5s with similar traffic (atterns and characteristics. A highway lin5 is defined for traffic count (ur(oses as a homogeneous section that has the same traffic characteristics' such as AA&T and daily' wee5ly' and seasonal variations in traffic volumes at each (oint. 7road classification systems for major roads may include freeways' e!(ressways' and major arterials. 6or minor roads' classifications may include residential' commercial' and industrial streets. %ontrol %ounts. These counts are ta5en at stations 5nown as control,count stations' which are strategically located so that re(resentative sam(les of traffic volume can be ta5en on each ty(e of highway or street in an area,wide traffic counting (rogram. The data obtained from control counts are used to determine seasonal and monthly variations of traffic characteristics so that e!(ansion factors can be determined. These e!(ansion factors are used to determine year,round average values from short counts. Control counts can be divided into major and minor control counts. Major control counts are ta5en monthly' with 2",hour directional counts ta5en on at least three days during the wee5 ;Tuesday' >ednesday' and Thursday< and also on aturday and unday to obtain information on wee5end volumes. /t is usual to locate at least one major control,count station on every major street. The data collected give information regarding hourly' monthly' and seasonal variations of traffic characteristics. Minor control counts are five,day wee5day counts ta5en every other month on minor roads.
%overa!e %ounts. These counts are used to estimate A&T' using e!(ansion factors develo(ed from control counts. The study area is usually divided into )ones that have similar traffic characteristics. At least one coverage count station is located in each )one. A 2",hour non,directional wee5day count is ta5en at least once every four years at each coverage station. The data indicate changes in area,wide traffic characteristics. 1;. 5(plain the representation of volume count Traffic Volume #ata $resentation The data collected from traffic volume counts may be (resented in one of several ways' de(ending on the ty(e of count conducted and the (rimary use of the data. &escri(tions of some of the conventional data (resentation techniues follow. Traffic *lo 7aps These ma(s show traffic volumes on individual routes. The volume of traffic on each route is re(resented by the width of a band' which is drawn in (ro(ortion to the traffic volume it re(resents' (roviding a gra(hic re(resentation of the different volumes that facilitates easy visuali)ation of the relative volumes of traffic on different routes. >hen flows are significantly different in o((osite directions on a (articular street or highway' it is advisable to (rovide a se(arate band for each direction. /n order to increase the usefulness of such ma(s' the numerical value re(resented by each band is listed near the band. 6igure ".13 shows a ty(ical traffic flow ma(. Intersection Summary Sheets These sheets are gra(hic re(resentations of the volume and directions of all traffic movements through the intersection. These volumes can be either A&Ts or Ps' de(ending on the use of the data. 6igure ".1" shows a ty(ical intersection summary sheet' dis(laying (ea5,hour traffic through the intersection. Time02ased #istribution %harts These charts show the hourly' daily' monthly' or annual variations in traffic volume in an area or on a (articular highway. ach volume is usually given as a (ercentage of the average volume. 6igure ".1# shows ty(ical charts for monthly' daily' and hourly variations.
*i!ure +.1" !am(le of a Traffic
*i!ure +.1+ /ntersection ummary heet
6low Ma( 1<. #efine traffic capacity? 'ist the factors affectin! capacity
/t is the ability to accommodate traffic volume. /t is the ma!imum hourly rate at which vehicles can reasonably be e!(ected to cross a (oint on a roadway during a given time (eriod under (revailing traffic conditions 6actors affecting highway ca(acity 1. :ane width 2. >idth of the shoulders 3. :ateral clearance ". Commercial vehicles #. 0oad alignment and geometry $. !istence of intersection %. 4ne way or two way traffic *. &river and vehicle characteristics +. (eed 1-. >eather condition 11. Par5ing condition 12. Presence of (edestrians
