Menaxhin Trafiku *versioni anglisht*

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Menaxhin Trafiku *versioni anglisht*

  1. 1. Traffic ManagementHamit DanajPolitecnic University of TiranaSafetyJanuary 2011Time spent: 13 hrs
  2. 2. Road network and functionalhierarchy Traffic management is a process ofadjusting or adapting the existing roadnetwork to improve traffic operationswithout major construction Traffic management objectives may include Traffic efficiency• Road capacity Improved environment amenity• Reduced noise
  3. 3. Traffic management objectives(continued) Enhanced access• Better access for particular group of roadusers• Pedestrians• Bicyclists• Freight vehicles Road safetyThese objectives may potentially be inconflict of each other, so priorities mayhave to be determined.
  4. 4. Road functions and functionalhierarchy The use of traffic management to pursuesafety objectives must take place in thecontext of a clear view of the functions of aroad network, which is referred to asfunctional hierarchy. Road’s function is the prime determinant ofthe management of any given road withinthe overall network.
  5. 5. Road functions and functionalhierarchy (continued) There are essentially two needs from aroad function point of view The traffic movement function• The role of roads in providing a means to transferpeople and goods from one place to another; theseroads constitute the arterial road network The access function• The role of these roads is providing access to abuttingproperties and land uses; these roads constitute thelocal road networkIdeally each road would perform one of thesefunctions, but in practice there are many roadsthat perform both functions
  6. 6. Road functions and functionalhierarchy (continued) The only roads that do not have an accessfunction are those which are accesscontrolled The only access is via ramps at interchanges• Freeways Access from abutting property is oriented awayfrom the road• Sometimes done with distributor roads in residentialneighborhoods Access via frontage roads paralleling an arterialroads
  7. 7. Road functions and functionalhierarchy (continued) The roads which carries both functions ofaccess and mobility, create a majorchallenge for traffic management Tend to have very poor crash record as a resultof their mixed and inherently conflictingfunctions People living and working along them seek touse them for• Access purposes• Exiting and entering properties• Parking in the street Have significant pedestrians and bicycleactivities in residential areas
  8. 8. Road hierarchy as a networkplanning tool The basis for any traffic management plan isusually the development of road hierarchy andagreement to it by various stakeholders. Main objectives Prevent residential areas being used by throughtraffics Influence driver behavior to follow planned routes atmoderates speeds, with proper attention being givento pedestrians and bicyclists Use physical devices in support of legal regulations inorder to overcome the lack of enforcement for suchmeasures as speed limits, one way streets andturning prohibitions.
  9. 9. Road hierarchy as a networkplanning tool (continued) Local roads, which have solely an accessfunction, will have objectives related tolocal amenity and safety If road configuration does not allow theseobjectives to be met, then there is a need forsome form of treatment Similarly roads with mixed functions will needsome kind of treatment in order to satisfactoryachieve both safety and mobility There is also an urban space which is motorvehicle-free• Mobility is solely provided by walking and bicycling
  10. 10. Road hierarchy as a networkplanning tool (continued) Gunnarsson defines three classes of road F (exclusive foot space) C (local street) T (exclusive transport space)This provides a conceptual framework for trafficcalmingTF CF/CT/CGunnarson describes local street (zone C) and twotransition zones (F/C and T/C) as “traffic calming space”
  11. 11. Lessons for new network Wallwork (1993) said: “Traffic calming is a negative reaction to aproblem caused by bad planning, zoning and/orstreet design. We need to be proactive in ourapproach and learn from the past and others” This is mainly involve• Attention to network layout• Ensure that problems are not built in• Attention to detail in civic design• To ensure that an appropriate balance of built andopen spaces and the connection between them areprovided
  12. 12. Lessons for new network(continued) Research for the safety aspects of roadnetwork design summarized the keynetwork planning principles for newresidential areas as follows Strict differentiation of streets according to theirtraffic function leads to safer residential areas Distribution of traffic into residential area withmultiple access from a ring road is safer thancentral distribution
  13. 13. Lessons for new network(continued) Full segregation of vehicle, pedestrians andbicycle movements is accompanied by very lowaccident rates Cul-de-sac streets are safer than loop streets,which in turns are safer than ordinary throughstreets Crash rate is minimized where frontage accessis prohibited
  14. 14. Traffic management or trafficcalming There have been many differentinterpretations of traffic calming in differentcountries A useful resolution of this conflict ofinterpretation has been proposed by Brindle Traffic calming is used encompasses two axes• The scope of the measure• Local, intermediate or citywide• The type of measure• Use of physical devices and regulations• Social/cultural change
  15. 15. Area treatments Area treatments divided into twodistinct types Applicable to low density residentialdevelopment• Aim to control speeds which are in excessof a statutory speed limit of around 30-35mph Used in higher density cities• Aim is to reduce speed to around 20 mph
  16. 16. Area treatments (continued)Safety effectiveness Traffic management schemes are usually successfulin reducing• Vehicle speeds• Sometimes traffic volumes• But whether they increase objective safety; asmeasured by accident, is open to question An in depth analysis of accident pattern within casestudy area in Sydney concluded that• Many of traffic management devices used extensivelyin local area fail to resolve the dominant types ofaccidents occurring on local streets
  17. 17. Area treatments (continued) The dominant types of accident were Cross traffic Right-through Rare end Hit parked vehiclesLocal area traffic management schemes may notbe as effective in reducing accidents as manypractitioners believeHowever, there were several studies which haverevealed the positive effects of trafficmanagement schemes
  18. 18. Area treatments (continued)Environmentally adapted through roads This is one which retains its status as anarterial road• Traffic efficiency role is curtailed, so otherenvironmental or amenity goals may also berealized There are two typical application• Bypass towns• Adaptation of roads still fulfilling theirarterial function
  19. 19. Area treatments (continued) In either case, treatments typically involvesome or all of the following A form of gateway treatment using signs andtown entry features to• Emphasize the changed status of the road• Encourage slower driving• Provide a sense of identity Speed restricting devices• Road narrowing• Road humps Enhanced pedestrians and bicyclists facilities
  20. 20. Area treatments (continued) Improved parking especially for bypass towns• The town can rejuvenate as a business center whenthrough traffic is removed Change traffic furniture like lighting and seating Enhanced signing A roundabout at the start and end of the town• To ensure traffic slows Narrower lanes Change in road surface including color and texture Additional traffic control measures• Traffic signal• Pedestrian crossing
  21. 21. Area treatments (continued)Problems and difficulties There is a negative response from affectedparties which needs to be considered Brindle (1992) reported a citizen groupopposition to traffic calming (especiallyspeed humps) in the following terms They discriminating against law-abiding roadusers They are dangerous to bicyclists and motorcyclists, especially when wet
  22. 22. Problems and difficulties(continued) They cause unnecessary wear and tear on motorvehicles They disadvantage some local businesses Their lighting is a source of annoyance to someresidents They hinder emergency vehicles They waste taxpayer’s money They make some motorists more aggressive andimpatient They detract from the environment• lights, signs, noise
  23. 23. Problems and difficulties(continued) They devalue property They are inappropriate for heavy vehicles They increase road maintenance costs They cost people timeSome of these points are not without validityconsiderations such as these mean that thedevelopment of traffic calming schemesrequires careful design and sensitiveimplementation
  24. 24. Speed management Speed may be managed in two ways Traffic calming• Using physical devices aimed to restrict thespeed of vehicles Imposition of speed limitsSpeeds and safety There is clear evidence of the effect ofspeed on accident rates As travel speeds drop, the impact speedsdrop, and collision may be avoided
  25. 25. Speed management (continued) Organization for Economic Cooperation andDevelopment has quantified the effect of speed onaccidents and accident severity, based on Swedishdata The percentage drop in accident rates outside built up areais n times the percentage drop in mean speed• n = 4 for fatal accidents• n = 3 for injury accidents• n = 2 for all accidents In urban areas, there are two distinct speed relatedaccident problems Injury to drivers and passengers of vehicles where speed isin excess of posted speed limits
  26. 26. Speed management (continued) Injury to vulnerable road users• Pedestrians and bicyclists• In many cases the driver is within the speed limit• McLean, et al, 1994 based on a detailed study of 146 fatalpedestrian crashes found that 45 percent of these wouldprobably survived if vehicle struck them with 10 km/h slowerspeedSpeed Limits Speed limits affect travel speed and therefore shouldaffect accidents specially in urban areas and roads withlimited design standards There is less clear evidence of affect of speed limits oncrashes in rural areas Different studies found different results on affect ofincreasing speed limit in rural areas
  27. 27. Speed limits and travel speeds Speed limits affect safety only if they affectactual travel speed The influence of speed limit relies Reasonableness of speed limit as perceived bydriver On enforcementReasonableness of speed limits ‘In order to bring about a reduction in meanspeed and speed dispersion, a speed limit shouldbe set at 85 percentile of existing speeds, or at alower level ( but not too far below)’
  28. 28. Reasonableness of speed limits(continued) Road environment factors affecting theperception of driver about the reasonableness ofspeed limit• Alignment• Urban or rural environment• Road category• Lane width• Roadside development• Traffic density• Sight distance• Parked vehicles• Pedestrians• Day and night vision
  29. 29. Enforcement Enforcement would result in a reduction inmean speed and in the spread of speed This will lead to reduction in crash number andseverity Automated speed enforcement have beeneffective in reducing speed• Not only on the site where they have been set up• But also in leading to a change in attitudes towardsspeeding• The wide spread use of speed cameras has alreadyproduced a change in driver attitude in Australiawhere portable speed cameras have been in use forseveral years
  30. 30. Differential speed limits for heavyvehicles ‘There is evidence that accident rates arerelated to the dispersion or variance ofspeeds of vehicles in the traffic stream’ Many different studies reported the chanceof being involved in an accident follows a U-shaped distribution (Figure 13.4 page 335) The minimum occurring when the vehicle istraveling at about the average speed of traffic,or slightly above As vehicle speeds move significantly above orbelow the average speed, the probability ofbeing involved in a crash increases dramatically
  31. 31. Differential speed limits for heavyvehicles (continued) There is an argument that there should not be aspeed limit differential between heavy vehicles andother road vehicles Evidence to support this produced in US following theintroduction of nationwide 55 mph car speed limits in1974, the observed speed differential between cars andtrucks was reduced Radwan and Sinha examined the effect of this on truckaccidents and found• There had been reduction in heavy truck crash rates in allseverity types (fatality, injury and PDO) on freeways• On four-lane and two-lane rural highways, the reductionoccurred only for injury crashes• The reductions were attributed to an absolute reduction inspeeds and decreased speed dispersion
  32. 32. Setting speed limits There are four types of speed limits1. General limits Impose by statute and are applicable to allroads in an area unless signed otherwise A general urban or rural limit1. Speed zones Speed limits applied to a specific roaddepends on the road’s design characteristicsand its traffic and land use characteristics Varying by time of day
  33. 33. Setting speed limits (continued)3. Vehicle limits Apply to specific classes of vehicle Trucks and buses4. Driver limits Apply to specific classes of driver LearnersFormal management of vehicle speedsusing any of these legally enforceablespeed limits involves• Establishing a balance between safety,mobility, and amenity for users
  34. 34. Setting speed limits (continued)• Meeting driver expectation• Making speed limits more or less self enforcing• Achieving consistency across the jurisdiction• Ability to deter offenders by appropriate levelsof enforcement• Developing a culture of compliance• Minimizing the cost of signing and enforcement A systematic approach to setting speed limits in aspeed zoning context is the expert system calledVLIMITS developed by the Australian RoadResearch Board which considers the factors shownin Table 13.1 page 339
  35. 35. Setting speed limits (continued) VLIMITS is used as a basis for a majorstatewide speed limit review in Victoria The guidelines to use various speed limits areas follow Shared zone (6 mph)• Vehicles and pedestrians sharing the same road space• Service vehicles in shopping malls Local traffic area zone (24 mph)• Traffic management works have been undertaken tophysically limit the speed Local street speed limit (30 mph)• Local access or collector roads with abutting
  36. 36. Setting speed limits (continued) General urban limit (36 mph)• Applies to all urban roads that do not meet thecriteria for higher or lower speed limit• Undivided or divided arterial roads with substantialabutting development• Collector roads with higher standard• 25 ft between curbs and carrying above 5000 vpd Urban (42 mph)• Divided roads with direct access to throughroadway• Undivided roads with low traffic volumes, littleor no abutting development
  37. 37. Setting speed limits (continued) Urban (48 mph)• Divided roads with substantial abutting developmentwith little or no direct access• Undivided roads with limited amount of abuttingdevelopment General rural limit (60 mph)• Little or no abutting development and widely spacedintersection Rural freeway (66 mph)• Applies to high standard rural freeways• meet the current design standards• Have a 30 ft roadside clear zone• Accident rate of less than one fatal accident per 1.2 milesper year• Widely spaced interchanges (greater than 2 miles)
  38. 38. Devices and techniques formanaging speed and volume Type of devices and techniques availablefor keeping speed low falls into sixcategories1. Regulatory devices Speed limits Stop and yield signs No-turn signs One-way operation1. Network modifications Street closure at intersection Link closure
  39. 39. Devices and techniques for managingspeed and volume (continued) Partial street closure Diagonal closure of intersection• Placement of a barrier diagonally across a cross-intersection, to create two right-angle bends instead ofan intersection Closure of median opening Pedestrian refuge and/or narrow median3. Devices used at intersections Roundabouts• Resolves priority issues in local streets• Vehicle is required to divert from a straight line• Reduce vehicle speed
  40. 40. Devices and techniques for managingspeed and volume (continued) Klyne (1988) established an empirical relationship betweenspeed and path radiusV=6√R/SV = 95 percentile speed (km/h) of throughvehiclesR = radius of centerline of vehicle path (meters)S = sight distance factor (S=1.0 for good sightdistance, up to 1.53 for poor sight distanceThis formula suggests that to keep 95 percentile speedsthrough an intersection to 30 km/h, the roundaboutgeometry should be such that the path radius developedcan not be greater than 80 feet
  41. 41. Devices and techniques for managingspeed and volume (continued) Channelization To reallocate priority at an intersection• At t-intersection to give priority to vehicles travelingaround a curve To deter speeding by motorists on the top ofthe t-intersection by requiring them to slowdown to negotiate the device3. Devices relying on vertical displacement Road humps• Bump• A pipe half –buried which can potentially damage the vehicleand cause loss of control
  42. 42. Devices and techniques for managingspeed and volume (continued)• TRRL or Watts profile hump• Circular in shape, about 2 to 5-inches high and 10-13 ft in length• Flat-topped or plateau road hump• Similar in effect with circular humps but more userfriendly (Figure 13.11 page 349)• Has straight approach and departure ramp(typically 1:10 to 1:15) and a flat top,• Length of flat top varies from 7 to 24 ft, so thatvehicle has both axle on plateau• Rumble devices• May be placed transversely across the pavement toalert the driver to approaching hazard• Intersections or pedestrian crossing
  43. 43. Devices and techniques for managingspeed and volume (continued)3. Devices relying on horizontal displacement Chicanes• Feature extending into the roadway from the curbwhich referred to as “build outs” in UK and “curbextensions” in Australia (Figure 13.12 page 351) Pinch points• Sometimes referred to as “slow points” is a shortsection of a narrow road• Introduces a sudden change in road configuration(Figure 13.13 page 352) Restructured parking• Rearrangement of parking can be an effective speedcontrol measure (Figure 14.2 page 371)
  44. 44. Devices and techniques for managingspeed and volume (continued)3. Gateways May be used at the entrance to towns toannounce the start of the build upenvironment with devices such as• Pinch points• Changes in surface texture and/or color• Road humps• Signing• Landscaping features• Planting• Street furniture
  45. 45. Implementation of devices Useful guidelines in implementing devicesintroduced based on worldwide researches Network configuration should be such that theamount of traffic volumes in residential streetsare in the range of 2000-3000 vpd Wide, long streets with house frontages have apoor safety record and should be avoided Network discontinuities can be made todiscourage the entry of non-local traffic Intersections along street within the residentialnetwork should be separated by at least 70 ft
  46. 46. Implementation of devices(continued) Action is usually required when 85 percentilespeeds exceed 35 mph The effect of speed control devices is localized,which introduce the following relationshipsbetween 85 percentile speeds and spacing• 18 mph : 250 ft spacing• 24 mph : 330 ft• 27 mph : 500 ft• 36 mph : 670 ft Chicanes should not be used when traffic volumeexceeds 600 vph
  47. 47. Implementation of devices(continued) Chicanes will constraint vehicle speed to lessthan 20 mph if it is 30-45 ft long Chicanes and road humps should only used onstraight sections Rumble devices can be problem for bicyclists andpedestrians• They should not exceed 0.6 inches in height and a gapof about 30 inches be left between the device and curbto allow passage for bicycles Road humps lower than 2 inches give virtuallyno slowing effect
  48. 48. Parking An important task for traffic management ishow and where to store the vehicles sincethey are spending the majority of their timeat rest Parked or parking vehicles are particularlyassociated with pedestrian fatalities Ross Silcock Partnership suggest that planning forparking involves consideration of three factors• The need to maximize access to traffic generatingfacilities• The need to minimize interruption to moving traffic• The need to minimize traffic accidents
  49. 49. One-way streets One-way streets tend to be inherently saferthan two way streets Friction from an opposing traffic stream has beenremoved Generally one-way operation leads to Higher speeds and longer trips Fewer stops Traffic flow tends to be more orderly More confusing for pedestrians, but on the otherhand conflicts at intersections are reduced Pedestrian accidents and accidents at low volumeunsignalized intersections are particular problems
  50. 50. Truck routes Control of trucks through truck routing is ameans of implementing an urban trafficmanagement scheme Its application is to pursue amenity objectives, notsafety objectives The only reference from the safety stand point isto trucks routing of hazardous materials Certain ideal guidelines from a number of studiesto address the routing for trucks which arecarrying hazardous materials are as follow:• All freeways and control access facilities are likely to besuitable
  51. 51. Truck routes (continued)• Routes should be as direct as possible• Routes should be less densely populated• Routes should avoid the centers of populationconcentration, such as schools, shoppingcenters, hospitals and so on• Routes should possibly be free of physicalcharacteristics, such as low overheadclearance, steep grades, narrow lanes• Rail level crossing should be avoided• Crossing over open water supply should beavoided

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