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61 APPENDIX F Traffic Information Program Series (TIPS) These briefs are reprinted with permission from ITE and are available on the ITE website: (http://www.ite.org/councils/tengineering.htm#tips) The Institute of Transportation Engineersâ Traffic Engineering Council has produced a series of information and fact sheets that address common questions relating to transportation. The Traffic Information Programs Series (TIPS) answer frequently asked questions about many aspects of transportation planning, traffic operations, and traffic control. The TIPS are written in lay language so they serve as an information source not only for transportation professionals, but for the general public as well. The TIPS are formatted so that they can be copied on to a single piece of paper and placed in a notebook or folder. The TIPS format also allows for their mailing as a tri-fold self-mailer. A box on each TIPS is where the senderâs and recipientâs address can be placed. â¢ Bicycling â¢ Bus Signs â¢ Citizen Participation â¢ Construction Signs â¢ Four-Way Stop Signs â¢ HOV Lanes â¢ Lower Speed Limits â¢ Maximizing Transportation Operations â¢ Median Treatments â¢ Right of Way Regulations â¢ School Zones â¢ Sign Shapes â¢ Speed Humps â¢ Speed Limits â¢ Stop Sign and Bar Placement â¢ Stop Signs â¢ Traffic Engineering â¢ Traffic Sign Colors â¢ Traffic Sign Types â¢ Traffic Signal Warrants â¢ Tree Removal â¢ Turn Lanes Note: Additional briefs are contained in âNeighborhood Traffic Controlâ (see the annotated references in Appendix C).
62 Bicycling In the National Bicycling and Walking Study, the U.S. Department of Transportation set national goals for bicycling and walking. The goals proposed are: # To double the current percentage (from 7.9% to 15.8%) of total trips made by bicycling and walking; and # To simultaneously reduce by ten percent the number of bicyclists and pedestrians killed or injured in traffic crashes. According to 1996 statistics from the National Highway Traffic Safety Administration, 761 bicyclists were killed and an additional 59,000 were injured in traffic crashes, whereas 5,412 pedestrians were killed and 82,000 were injured in traffic crashes. Several actions can be taken to improve bicycling conditions and encourage the use of bicycles. The following are the steps for a model strategy that can be used to improve conditions for bicycling in your community: # Develop policies and plans to support bicycling; # Provide adequate infrastructure of bicycle travel and supporting facilities; # Provide public education and awareness; and # Provide incentives and eliminate disincentives for bicycling. Federal funds are available for bicycle- pedestrian facilities through several categories within the federal transportation legislation (TEA- 21), most notably the Transportation Enhancements and Congestion Mitigation/Air Quality categories. Nearly $200 million of these federal funds have been spent every year since 1992 for bicycle and pedestrian facilities. The following sections describe the steps of this model strategy. Develop policies and plans to support bicyclingâ The development of policies and plans to support bicycling should be first and foremost in any bicycle strategy. The policy statements and plans will help set the direction of the remaining steps and actions to be taken. Policies and plans should be developed with input from various user groups in the area (e.g., bicycling clubs, advocacy agencies, etc.). Policy statements can be something as simple as âThe City of Anywhere supports and encourages bicycling for
63 transportation and recreation, as it reduces congestion, improves air quality, and enhances this communityâs quality of life.â Bicycle plans should address a number of issues, including a policy statement, goals and objectives, existing conditions and/or problem areas, and a recommended strategy (with action items and measurable benchmarks) for improving conditions for bicycling. Facility design guidelines are also commonly incorporated into bicycle plans. Provide adequate infrastructure of bicycle travel and supporting facilitiesâOnce the necessary bicycle policies and plans have been formulated, the bicycle travel and supporting infrastructure should be provided to support bicycling throughout the community. Bicycle travel and supporting facilities include: # Shared roadway/wide curb lanes (Class IV); # Signed bicycle routes (Class III); # Bicycle lanes (Class II); # Separated bicycle paths (Class I); and, # Bicycle racks/parking. The bicycle plan developed in the previous step should provide guidance on the type and design dimension for bicycle facilities. With bicycling, the quality of the trip is part of the motivation for bicycling, and is affected by vehicle interaction, route continuity, directness, and connection to desired land uses. These factors should be taken into consideration when providing bicycle facilities in your community. The resource section at the end of this article provides bicycle facility design guidelines. Bicycle racks/parking should be provided at popular bicycling destinations, such as public libraries, parks, shopping centers, schools, and other locations where the existing presence of bicycles indicates a need for bicycle parking. Provide public education and awarenessâPublic education and awareness efforts are necessary for several reasons: # To encourage potential bicyclists by informing them of the benefits of bicycling; # To provide information about bicycle safety and operating a bicycle in motor vehicle traffic; # To inform bicyclists and motorists of their legal rights and obligations for operating under the same rules and regulations; and # To provide training for potential bicyclists. Provide incentives and eliminate disincentives for bicyclingâAt a minimum, various incentives can be provided to bicyclists, or disincentives can be eliminated, to encourage bicycling. Disincentives to bicycling that should be eliminated include things such as: # muddy paths; # no space for bicycles on high-speed roadways; # hazardous roadway conditions such as debris or drainage grates; and # no bicycle parking/racks. Incentives that can be provided to encourage bicycling include things such as: # travel time savings compared to motor vehicle travel (due to dedicated facilities, location of parking, etc.); # aesthetic and/or recreational value, such as shared-use paths along greenways; # convenient access to businesses; and # shower and changing facilities at workplaces.
64 What is the law concerning school buses? School buses can be identified by their unique yellow/orange color; black âSCHOOL BUSâ and number or district markings in black; and the red and yellow (and now strobe) lights at the top of the bus. When meeting a school bus with red flashing lights, you must stop when approaching the bus from either direction. School bus drivers usually flash yellow warning lights before stopping to load or unload passengers; when you see them, slow down and prepare to stop. Once stopped for a school bus, you may not proceed until the red lights stop flashing or until a traffic officer waves you on. If you are driving on a separate roadway from the one the school bus is on, you do not need to stop when passing or meeting a school bus. Also, you donât have to stop if you are traveling on a controlled access highway and the school bus is stopped in a loading zone which is part of or adjacent to the highway and where pedestrians are not allowed to cross the roadway. Bus Signs
65 Why include this? The School Bus Stop Ahead sign may be used when a school bus stopped to load or unload passengers is not visible for a distance of 500 feet in advance. This sign is not intended for use everywhere a school bus stops: it should be used only where terrain and roadway features limit the sight distance and where there is no opportunity to relocate the stop to another location with adequate visibility.
66 Citizen Participation What can a citizen do to help reduce traffic accidents? A primary goal of any traffic engineer is to make our roadways as safe as possible. The public plays an important role in achieving that goal. Road users, whether they are driving, walking or cycling, are our eyes in the street. Citizens can do their part to help reduce the high cost of traffic crashes by taking the following actions: # Drive Carefully - Concentrate on driving and use seat belts; do not speed or drink while driving. # Don't Take Chances - Play it safe. Drivers should not try to "beat the light" or "beat the train" at railroad crossings. Drive defensively at all times. # Report Roadway Hazards as soon as possible to city, county or state officials responsible for road maintenance and safety. Roadway hazards that should be reported are: . Traffic signs down or damaged. . Traffic signal malfunctions. . Traffic signs obstructed by vegetation. . Street lights that are burned out. . Shoulder washouts. . Obstructions, potholes, bumps or dips in roadway. . Water ponding on roadway. # Property Owners Should Keep Vegetation Trimmed to ensure that good intersection and driveway sight distances are provided and that traffic control signs and signals are visible.
67 # Report Acts of Vandalism to law enforcement, traffic engineering and maintenance officials. # Support Traffic Safety Officials to ensure that they have adequate budgets for staff, equipment and supplies to do their jobs properly. # Turn on Vehicle Headlights between dusk and dawn and anytime visibility is reduced by rain, smoke, fog, etc. # Keep Vehicles in Good Mechanical Condition by regularly checking brakes, tires, wipers and other safety equipment. # Obey Traffic Control Devices such as signs, signals and pavement markings. These devices were installed to enhance safety.
68 Why are those orange signs around road construction sites? Whenever work is done on or near the roadway, drivers are faced with changing and unexpected traffic conditions. These changes need to be conveyed to motorists, bicyclists, and pedestrians to ensure their safety and protect the workers. Drivers and pedestrians should take special care to observe signs, signals, pavement markings and flaggers near roadway construction sites. Special traffic control devices (usually a black legend on an orange background) are installed to assist and safely guide and protect motorists, bicyclists, pedestrians and workers in a work zone and warn them of unexpected roadway or traffic conditions. Most traffic control zones are divided into the following areas: ! Advance Warning Area - tells drivers what to expect. ! Transition Area - begins to move traffic from its normal area. ! Buffer Space - provides protection for traffic and workers. ! Work Area ! Termination Area - directs drivers to resume normal driving. Construction and maintenance warning signs are a special series with the black legend on an orange background. The orange color is used to indicate the temporary nature of the condition and the additional potential hazard of the worksite. Traditionally, work activities have included construction, maintenance, and Construction Signs
69 utility operations. However, orange color warning signs have application for all work activities within the right of way such as survey crews or temporary weighing stations. Construction detour routing signs may have a black legend on an orange background. Special information signs relating to the work being done must also have a black message on an orange background.
70 Four-Way Stop Signs Why canât we have an all-way stop to reduce accidents? Many people believe that installing STOP signs on all approaches to an intersection will result in fewer accidents. Effects of unwarranted stop signs on driver behavior and safety are difficult to substantiate. Also, there is no real evidence to indicate that STOP signs decrease the overall speed of traffic. Impatient drivers view the additional delay caused by unwarranted STOP signs as âlost timeâ to be made up by driving at higher speeds between STOP signs. Unwarranted STOP signs breed disrespect by motorists who tend to ignore them or only slow down without stopping. This can sometimes lead to tragic consequences. Generally, every State requires the installation of all traffic control devices, including STOP signs, to meet state standards of the Department of Transportation. The state standards are based on the Manual on Uniform Traffic Control Devices (MUTCD). The MUTCD is published by the U.S. Department of Transportation, is the national standard for traffic control devices. The MUTCD prescribes standards for the design, location, use and operation of traffic control devices. The installation of multi-way stop control must first meet the warrants as set forth in the MUTCD. Any of the following conditions may warrant an all-way STOP sign installation: 1. Where a traffic signal is warranted, multi-way stop control is an interim measure that can be implemented
71 quickly to control traffic until the signal is designed and installed. 2. The occurrence within a twelve-month period of five or more reported accidents of a type susceptible to correction by multi-way stop control. Such accident types include turn collisions, as well as right-angle collisions. 3. Total vehicular volume entering the intersection from all approaches must average 500 vehicles per hour for any eight hours of an average day and the combined vehicular and pedestrian volume from the minor street or highway must average at least 200 units per hour for the same eight hours, with an average delay to minor street vehicular traffic of at least 30 seconds per vehicle during the maximum hour. However, when the 85th percentile speed of traffic approaching on the major street exceeds 40 miles per hour, the above minimum volumes are reduced to 70 percent. STOP signs should not be viewed as a cure-all for solving safety problems but, when properly located, can be useful traffic control devices to enhance safety for all roadway users.
72 HOV Lanes What is an HOV Lane? In recent years, high-occupancy vehicle (HOV) lanes have become a successful alternative transportation mode in areas with heavy traffic congestion. HOV lanes are sometimes termed commuter lanes, busways, or transitways. Although known by several names, they all refer to one or more roadway lanes allocated for special use. Special use may be defined in several ways, including passenger vehicles with 2 or 3+ people, transit vehicles, and sometimes motorcycles, taxis, or trucks. Priority pricing, allowing single-occupant vehicles to âbuy intoâ HOV lanes, is also being evaluated. HOV facilities may be used to improve the mobility of a corridor by: C Increasing the people-moving capacity of the facility; C Providing a reliable travel-time savings to HOV users; and C Providing an incentive for people to share rides. The basic concept of an HOV lane is to encourage an increase in the number of persons traveling in a vehicle by providing a reliable travel time savings to select vehicles (e.g., buses, vanpools, and motorcycles) or other vehicles meeting the minimum occupancy requirement. The occupancy requirement may be as low as 2 persons per vehicle, or may be as high as 4 persons. Increasing the number of HOVs in the corridor increases the average vehicle occupancy for the entire freeway. The increased person-movement results in improved freeway travel times during peak periods, improved transit service, and improved overall traffic flow. It may also decrease overall fuel consumption and vehicle pollution.
73 There are essentially four different types of high-occupancy vehicles (HOV) lanes used on freeways: â¢ Exclusive HOV Facility - Separate Right-of-Way. A roadway or lane(s) developed in a separate and distinct right-of-way and designated for the exclusive use of HOVs. â¢ Exclusive HOV Facility - Freeway Right-of-Way. Roadways or lanes built within the freeway right-of- way which are physically separated from the other freeway lanes but reserved for exclusive use by HOVs, at least during portions of the day. â¢ Concurrent Flow Lane. A freeway lane in the peak direction of flow (normally the inside lane) that is not physically separated from the other freeway lanes but is designated for use by HOVs at least for a portion of the day. â¢ Contraflow Lane. A freeway lane in the off-peak direction of flow (normally adjacent to the median) that is designated for use by HOVs traveling in the direction of peak flow for at least a portion of the day. Normally, the contraflow lane is âseparatedâ from the off-peak (or opposite) flow by insertable cones or pylons.
74 Lower Speed Limits Why not lower the speed limit to reduce hazards in our area? An unrealistically low speed limit can actually lead to accidents. Hereâs why: # First, many studies conducted over the last several decades in all parts of the country have shown that a driverâs speed is influenced more by the appearance of the roadway and the prevailing traffic conditions than it is by the posted speed limit. # Second, some drivers will obey the lower posted speed while others will feel itâs unreasonable and simply ignore it. This disrupts the uniform traffic flow and increases accident potential between the faster and the slower drivers. Research has shown that when vehicles travel about the same speed, accidents are minimized. # Third, when traffic is traveling at different speeds, the accuracy of the judgement of speeds by crossing pedestrians and motorists decreases. State Speed Laws Although each state has its own separate set of laws, speed limit laws are generally derived from very similar language. For instance, the foundation for most speed limits laws generally states that âNo person shall drive a vehicle on a highway at a speed greater than is reasonable and prudent under the conditions, and having regard to the actual and potential hazards, then existing.â
75 Maximizing Transportation Operations What can be done to provide a safe and efficient transportation system in existing or new development corridors? Traffic engineers are striving to provide roadway conditions that contribute to smooth and efficient traffic flow. Experience has shown that safety is enhanced by smooth traffic flow. Disrupting the smooth flow of traffic increases the probability of accidents. Erratic traffic operation may be caused by vehicles stopping or slowing in the roadway, passing and weaving maneuvers, uncoordinated or poorly timed traffic signals, the lack of guide signs, and unreasonably low speed limits. Slower speed does not insure safer traffic operation. The chances of a vehicle becoming involved in an accident are less when the driver is traveling at the average speed of traffic. The population growth in many areas poses great challenges for traffic engineers. These engineers are utilizing many traffic management techniques to ease and optimize traffic operations. These techniques include the following: C Interconnecting traffic signals located within close proximity of each other on a major street. C Installing computerized signal systems to improve traffic flow. C Limiting the number of driveways from new development. C Increasing spacing between driveways. C Limiting indiscriminate access to major roads by requiring connecting drives between adjacent shopping centers. C Providing access to driveways at signalized access points. C Providing adequate turning radii at driveways, to ease turning into entry and exit roads. C Providing turn lanes when needed. C Providing traffic control devices such as signs, pavement marking, and signals where necessary. C Installing bikeways and sidewalks where needed.
76 C Reducing new demand on the highway system by implementing techniques such as ride sharing and alternative work hours. C Promoting mass transit where feasible. Direct benefits to the public include improved safety and air quality and reduced travel cost due to a decrease in travel time. Safety can be enhanced by improving the uniformity of traffic flow and reducing the number of vehicles on the roadway. Air quality can be improved by reducing the number of stops and motorized vehicles on the road. Travel cost can be reduced by minimizing delays at traffic signals and in heavy traffic congestion.
77 Median Treatments Why are two-way left-turn lanes and raised medians used? The two most commonly used median treatments on urban and suburban arterials are two-way left-turn lanes (TWLTLs) and median islands. TWLTLs are typically employed in areas of moderate to intense roadside development where the demand for mid-block left turns is currently (or expected to be) high. With a TWLTL, left- turn access can be provided at any point along the roadway. For this reason, they are typically used on arterials where there are frequent and randomly organized access points. On the other hand, raised medians present a physical barrier to drivers and, as such, cannot be easily traversed. For this reason, raised medians are often used where it is desirable to prevent mid-block left turns. On roadways with raised medians, left-turn maneuvers are concentrated at established openings in the median or at signalized intersections. Both of these types of median treatments have advantages and disadvantages in terms of operations and safety. The primary advantage of a raised median is that left-turning traffic can be concentrated at established median openings. Raised medians have been found to reduce crashes 25 to 40 percent, depending on traffic volumes. This makes it easier to regulate crossing traffic. In addition, raised medians can be used to provide a refuge area for pedestrians crossing the roadway. The primary disadvantage of a raised median, however, is that it often increases the amount of travel time and delay experienced by some left-turning traffic. Because a raised median forces left-turns to occur at established openings only, some left-turning motorists must travel circuitous routes to reach their destination. This can lead to undesirable turning movements (e.g., u-turns on roadways with insufficient width) and unwanted travel patterns (e.g., traffic entering neighborhood areas). In addition, the raised median island can pose a potential safety hazard on streets serving high-speed traffic. If accidently struck, a raised
78 median could cause the driver to lose control of the vehicle. Furthermore, a raised median (particularly a narrow island) may be difficult to see at night unless a fixed lighting source is provided. The main advantage of a TWLTL is that it provides a storage area for left-turning vehicles as they wait for gaps in the opposing traffic stream. This not only improves the operations of through traffic by removing the left-turning vehicle from the traffic stream, but also reduces the potential for read-end accidents. When TWLTLs are installed on two-lane, undivided facilities, they have been found to reduce accidents by approximately 35 percent in suburban areas and from 70 to 85 percent in rural areas. Since turning traffic is not physically restricted in any way with TWLTLs, drivers can take more direct routes when entering and exiting adjacent properties. For this reason, drivers and adjacent property owners generally prefer TWLTLs over raised medians.
79 Right of Way Regulations What gives a public agency the right to dig up my front yard? Ask a homeowner where they believe the property line is in front of their house. In general, many will say that their property line ends at the curb or sidewalk. In fact, a homeownerâs property line ends somewhere behind the curb or sidewalk. If there is no sidewalk, then it ends a number of feet behind the edge of the traveled way or shoulder. The line that denotes the private/public property split is known as the right-of-way line. Although the sidewalk lies on the public property side, most towns charge the maintenance (i.e., shoveling of snow and keeping it free from obstructions) of the sidewalk and grassy area to the homeowner. The county or municipality has the right to excavate or widen the roadway as required for maintenance or rehabilitation work. (NOTE: Different municipalities or states may have different statutes or jurisdictional responsibilities. Consult you town or borough engineer for specific responsibilities and ownership issues). If the road work extends onto private property, then an agreement (known as an easement) is drafted between the public agency and the homeowner. This easement can be a temporary one (for construction, etc.) or a permanent one (for drainage inlets, pipes, etc.). In any event, no public agency (except of course, police and fire) has the right to infringe upon private property. In all cases, the owner must be contacted for permission. The nature of the work or project is explained to the owner along with the anticipated duration.
80 Sometimes, it is necessary for a public agency to acquire a piece of private property to facilitate a roadway improvement. In this case, the piece of property needed is bought by the public agency. The piece of property in question is assessed for value by the public agency and the appropriate documents are prepared (i.e., property acquisition mapping). The price set is agreed upon by both the public agency and the owner. Legal mechanisms are available to resolve disputes should both parties be unable to agree upon the fair market value of the property in question. Once bought, a new right-of-way line is indicated on appropriate documents (tax maps, etc.) and the once private property now becomes public property. In conclusion, a public agency does have the right to âdig upâ someoneâs front yard, provided the agency remains within its right-of-way. Right-of-way lines are often behind the actual roadway or curb line and facilitate maintenance and rehabilitation efforts, such as future widening of the road, if required. At no time can a public agency excavate or work on private property without first obtaining consent from the owner. Although sidewalks are within the public right-of-way, the owner of the property is usually responsible for sweeping them and removing snow.
81 School Zones School Crossing Sign What is the law with regard to school speed zones? Reduced speed limits may be desirable or necessary for school zones during the hours when children are going to and from school. Usually such school speed zones are only considered for schools located adjacent to highways or visible from highways. Pedestrian crossing activity is usually the primary basis for reduced school speed zones. Generally, each stateâs laws governing School Zones can be found in that stateâs Vehicle and Traffic Law literature. These laws typically include limitations in the amount of speed reduction and the reduced speed zone location. Once a reduced speed zone for a school area has been established (in accordance with law, after an engineering study or traffic investigation), the school speed limit sign is installed with two supplemental plaques. Above the speed limit sign, a black on yellow sign reads âSchool.â Below the speed limit sign, a black on white supplemental plaque defines when the school speed limit shall be enforced. Flashing beacons may also be added to the sign with the bottom mounted plaque reading, âWhen flashing.â In addition to the school speed limit sign, the School Advance Warning Sign may be used to in advance of established school crossings not adjacent to a school ground. Where used, the sign is generally erected 150 to 700 feet in advance of the crossing.
82 School Advance Sign The school crossing sign, sometimes confused with the school advance sign, is intended for use at established crossings including signalized intersections used by pupils going to and from school. The sign should be omitted at crossings controlled by stop signs. Only crossings adjacent to schools and those on established school pedestrian routes shall be signed.
83 Sign Shapes Why are traffic signs different shapes? Traffic signs convey information to travelers through their shape, color, message, and placement. The standard sign shapes and their respective meanings are: OctagonâExclusively for STOP signs Equilateral Triangle, Point DownâExclusively for YIELD signs CircleâExclusively for Railroad Advance Warning Signs and Civil Defense Evacuation Route Signs PennantâExclusively for NO PASSING ZONE signs DiamondâUsed for warning signs Rectangle, Longer Dimension VerticalâUsed for regulatory signs Rectangle, Longer Dimension HorizontalâUsed for guide signs TrapezoidâUsed for recreational area guide signs PentagonâUsed for school advance and crossing signs CrossbuckâUsed for railroad crossing signs Other shapesâUsed for route marker signs The objective of traffic signs is to convey traffic control information to the driver viewing them on the roadway.
84 Speed Humps Can speed humps be installed on my street? A speed âhumpâ is a raised area in the roadway pavement surface extending transversely across the travel way. Not to be confused with a speed hump, a speed âbumpâ is a raised area in a private driveway or parking lot. Speed hump dimensions and characteristics vary from agency to agency. They are typically 12 foot long by 3 to 4 inches high and are usually placed across the roadway between intersections. They are typically requested by residents as a means to slow traffic in residential neighborhoods or decrease the amount of âcut-thoughâ traffic. In general, speed humps may: 1. Reduce traffic speeds in the immediate vicinity of the speed humps, 2. Decrease traffic volume, and 3. Reduce accidents in some areas. At the same time, however, speed humps may also have the following detrimental effects: 1. Divert traffic to other neighborhood streets thereby moving the problem rather than solving it, 2. Increase noise level due to vehicle brakes, tires and engine, 3. Increase vehicle emissions due to deceleration and acceleration, 4. Increase response time of emergency vehicles, 5. Conflict with school and transit bus operation, 6. Present a potential hazard to bicyclists and motorcyclists.
85 Most agencies have a Speed Control Plan which either advocates the use of speed humps as a system wide tool to reduce speeds and/or vehicular volumes or eliminates their use unconditionally. When determining whether to install speed humps, the following restrictions may apply: 1. Streets serving transit buses. 2. Streets with daily traffic volumes above some predetermined threshold. 3. Streets designated as collector streets. 4. Rural roads. The Institute of Transportation Engineers has developed a report covering the design and application of speed humps. The report (Guidelines for the Design and Application of Speed Humps) was prepared by the ITE Technical Council Speed Humps Task Force in 1995. It can be obtained by contacting ITE headquarters at 202/554-8050.
86 Speed Limits How are speed limits established? In general, the governing body which has jurisdictional control over a roadway has the power to establish the speed limit for that roadway. This is done by adopting a resolution or by passing an ordinance to establish the speed limit. The Stateâs Department of Transportation gives the final authority to establish and enforce the speed limit. The matter of establishing the posted speed limit for a given roadway is a serious concern for the traffic engineer. It is based in part upon the characteristics of the roadway and its associated design speed. The design speed defines the values used for the design of a particular road and includes elements such as curve radii, stopping sight distance, and lengths of merges and tapers. Speed limits are also established in part by the drivers themselves. In order for a speed limit to be effective, it must be reasonable to the driver. Most drivers tend to regulate the speed of their vehicle relative to traffic, road and weather conditions. For a speed limit to be effective, the majority of the drivers must voluntarily comply with the law. It has been determined that the speed at which 85 percent of the motorists travel is reasonable and safe. The determination of the 85 percentile speed is made by conducting a speed survey of vehicles traveling along the roadway in question during normal operating conditions. Therefore, basing the speed limit upon this 85th percentile speed will insure a higher
87 level of compliance and create a reasonable uniform flow of traffic. Other factors which are also used in making a determination of the posted speed limit include road surface characteristics, shoulder condition, grade (i.e., steepness of the road), roadside development, parking practices, pedestrian activity, and accident experience. Once the engineering study has been completed and forwarded to the proper governing bodies for passage and approval, the required signs are then posted. Their placement and installation conforms to the Manual on Uniform Traffic Control Devices (MUTCD), which serves as the standard for the design, placement and installation of all traffic control devices. Speed limits cannot be posted in excess of legislatively mandated speed limits. From 1974 to 1995, the U.S. Congress also imposed the 55 mph National Maximum Speed Limit (NMSL). In 1995, Congress repealed the NMSL and returned control of maximum speed limits to the states.
88 Stop Sign and Bar Placement Where should a stop sign and stop bar (line) be placed at an intersection? In placing a STOP sign at an intersection, visibility of the sign by the motorist is of prime concern. The STOP sign should not be blocked by other signs or vegetation. It is placed on the right hand side of the traffic lane to which is applies. In cases where the road is wide, an additional STOP sign is placed on the left side of the road. Where two roads intersect at an acute angle, the STOP sign is positioned at an angle, or shielded, so that the message is out of view of traffic to which it does not apply. In order to provide adequate lateral clearance for the motorist who may leave the roadway in rural areas and strike the sign support, a STOP sign should be located at least 6 feet from the edge of the shoulder or if there is no shoulder, 12 feet, with a maximum of 14 feet from the edge of the traveled way. The height to the bottom of the STOP sign in rural areas should not be less than 5 feet or more than 8 feet above the edge of the roadway. In urban areas a lesser lateral clearance may be used where necessary. Although 2 feet is recommended as a working minimum, a clearance of 1 foot from the curb face is permissible where sidewalk width is limited or where existing poles are close to the curb. The height of the bottom of a STOP sign in urban areas should not be less than 7 feet or more than 8 feet above the top of the curb. In the case of stop bars, the MUTCD indicates that a stop bar (line) is a solid white line, normally 12 to 24 inches wide, extending across all approach lanes to a STOP sign or traffic signal. A stop bar should be placed parallel to the centerline of the intersecting street. A stop bar should be used in both rural and urban areas where it is important to indicate the point, behind which vehicles are required to stop, in compliance with a STOP sign, traffic signal, officerâs direction, or other legal requirement.
89 A stop bar, when used, should ordinarily be placed 4 feet in advance of and parallel to the nearest crosswalk line. In the absence of a marked crosswalk, the stop bar should be placed at the desired stopping point and in no case more than 30 feet or less than 4 feet from the nearest edge of the intersecting roadway. When a stop bar is used in conjunction with a STOP sign, it should be placed in line with the STOP sign. However, if the STOP sign cannot be located exactly where vehicles are expected to stop, the stop bar should be placed at the desired stopping point. Finally, the stop bar should be placed so that vehicles have optimum sight distance along the intersecting roadway.
90 Stop Signs How do you decide where to install STOP signs? STOP signs are traffic control devices that drivers encounter every day. They impose an inconvenience on the driver that cannot be ignored. Many drivers feel that more or fewer STOP signs are needed depending on the location and the time of day. Since they impose a significant amount of control over traffic, traffic engineers are very selective about STOP sign installation. In order to ensure that the advantages of installing a STOP sign outweigh the disadvantages, and to provide some consistency in the application of STOP signs, four warrants have been developed that define the minimum conditions under which further consideration of a STOP sign is appropriate. Using these warrants, traffic engineers look at an intersection based on various criteria: # Does a minor road intersect a major road where application of normal right-of-way rule is particularly hazardous? # Does a street enter a through highway or street? # Is the intersection an unsignalized one in a signalized area? # Does the combination of high speed, restricted view, and serious accident history indicate a need for a STOP sign? If one or more of these criteria describe the intersection, the traffic engineer then determines if a STOP sign is the best solution for the problem. It is important to note that a STOP sign should not be installed unless it meets one or more of the
91 warrants. However, if an intersection meets a warrant, a STOP sign does not have to be installed. The engineer should consider lesser control of the intersection, such as a YIELD sign, before installing a STOP sign. Some intersections may require a multi- way STOP sign installation as a safety measure. There are three warrants to help determine if multi-way STOP signs are needed at an intersection. The engineer performs the same analysis as that for two- way STOP signs. Many citizens believe that installing a STOP sign at an intersection will control speed along the roadway. However, unwarranted STOP signs can actually create other problems both at the intersection and along the roadway. When unwarranted STOP signs are used, drivers must stop more frequently. Thus, they tend to drive faster between intersections in order to save time. Unwarranted STOP signs also encourage disobedience and the use of alternate, inadequate routes. Properly located STOP signs can have various benefits. Aside from providing orderly traffic movement, they can reduce some types of accidents and allow minor street traffic to enter or cross a major roadway. Thus, before installing a warranted STOP sign, an engineer should determine that the STOP sign will improve the overall safety and/or operation of the intersection.
92 Traffic Engineering What is traffic engineering? The Institute of Transportation Engineers defines traffic engineering as âthat phase of engineering which deals with the planning, geometric design and traffic operations of roads, streets and highways...their networks, terminals, abutting lands and relationships with other modes of transportation...for the achievement of safe, efficient and convenient movement of persons and goods.â When roads and streets were built many years ago, the biggest task facing the road builder was to keep them passable in all types of weather. The problem of moving large numbers of cars and parking them was not significant. As the number of cars increases, taxing the capacity of our streets and highways, the field of traffic engineering has become increasingly prominent. Each year more people own and operate cars. Urban growth has increased the need for improving the movement of people and goods. Funding for new facilities has decreased due to resistance to higher taxes as well as energy and environmental concerns. This has resulted in an increased emphasis on finding ways to better use the existing road system as well as finding ways to better move people and goods. Examples of alternative solutions to these challenges include promoting travel during off-peak hours and the use of public transportation. The traffic engineer is concerned with groups and individuals and their needs, desires, actions, characteristics, capabilities and limitations as related to the roadway system. Decisions made by the traffic engineer affect drivers, passengers, and pedestrians.
93 Traffic Sign Colors Why are traffic signs different colors? The objective of traffic signs is to convey traffic control information to the driver. One manner in which signs accomplish this objective is through color. Each color used on a sign has a general meaning attached to it. Thus, the color alerts the driver of what to expect ahead. The Manual on Uniform Traffic Control Devices (MUTCD), a document published by the U.S. Department of Transportation, establishes standardized meanings for each color used in traffic signs. It also reserves three other colors for future use. The color code is as follows: COLOR MEANING Yellow General Warning Red Stop or Prohibition Blue Motorist Services Guidance Green Indicated Movements Permitted, Direction Guidance Brown Recreational and Cultural Interest Guidance Orange Construction and Maintenance Warning Black Regulation White Regulation Strong Yellow- Green Pedestrian, Bicycle, and School Crossings Purple Unassigned Light Blue Unassigned Coral Unassigned
94 Traffic Sign Types Traffic signs are classified as: ! regulatory signs ! warning signs, and ! guide signs. Regulatory signs give notice of traffic laws or regulations. Regulatory signs (except of STOP and YIELD signs) are typically rectangular in shape with the long dimension vertical. The standard color scheme is black lettering on a white background. A red circle with a white diagonal line may be used in conjunction with a black diagram to indicate a prohibited maneuver. Red is used as a predominant color for STOP, YIELD, DO NOT ENTER, and WRONG WAY signs. Warning signs call attention to conditions on, or adjacent to, a highway or street that are potentially hazardous to traffic operations. These signs are used particularly when the hazard is not obvious or cannot be seen by the motorist. Warning signs are typically diamond- shaped and have a black legend on a yellow background. Guide signs show route designations, destinations, directions, distances, services, points of interest, and other geographical, recreational, or cultural information. Destination guide signs typically have white lettering on a green background. Service and recreational
95 signs have blue and brown backgrounds, respectively. Other guide signs such as route designations may use a variety of colors depending on the type of road and state or local practice.
96 Traffic Signal Warrants What are traffic signal âWarrants?â In order to ensure that the advantages outweigh the disadvantages of installing a traffic signal, and to provide some consistency in the application of traffic signals, a series of warrants has been developed to define the minimum conditions under which further consideration of a traffic signal is appropriate. Simply meeting the warranting criteria does not mean that a signal is justified at a given location. There are many factors that impact the effectiveness of a signal, and all should be evaluated before a decision to install a signal is made. However, failure to meet any of the warranting criteria indicates that a traffic signal should not be installed, as there should be a better way of addressing the problems or needs at that location. Furthermore, if an existing traffic signal no longer meets any of the warrants, it should be removed. The traffic signal warrants currently contained in the national Manual on Uniform Traffic Control Devices (MUTCD) are summarized below. It is important to note that your local or state transportation agency may have modified or added additional warrants to the list below. Number and Title Basis 1 Minimum Vehicular Volume 8-hour volumes 2 Interruption of Continuous Traffic 8-hour volumes 3 Minimum Pedestrian Volume 4-hour pedestrian volumes and gaps 4 School Crossing number of school children and gaps 5 Progressive Movement signal progression 6 Accident Experience accidents and warrant #1, #2 or #3 volumes 7 Systems Warrant volumes 8 Combination of Warrants volumes and pedestrians 9 Four Hour Volume 4-hour volume 10 Peak Hour Delay volume and delay on minor street 11 Peak Hour Volume 1-hour volume
97 Tree Removal Why do they have to remove those trees next to my roadway? One of the most critical elements of design in considering the layout of a driveway or intersection is sight distance. The amount of sight distance required for a given circumstance is dependent upon a number of factors, including posted speed limit, and curves and hills. However, in all cases, clear and unobstructed sight of vehicles on both the travel way and intersecting street or driveway is of paramount concern. When trees were planted years ago, many of the current safety design standards did not exist. At the time the trees were planted, consideration was not given as to whether or not the line of sight to a driver would be impeded or whether motorists would hit the trees. Now, as the trees reach full maturity, their location may block a driverâs line of sight. Since the safety criteria for sight distance have been established, it becomes necessary to remove trees which cause a hazard to drivers by impeding their line of sight or creating a hazard along the side of the raod.. Design engineers try to save as many of the existing trees as possible when redesigning a road or planning driveway access, recognizing the aesthetic value of older trees. However, safety and proper design always take precedence. In many instances, when older trees need to be removed they are replaced with new plants. The new trees are planted in locations that will not impede a driverâs line of sight now or in the future. Besides blocking a driverâs line of sight, consideration must also be given to errant
98 vehicles that may stray from the travel way. If trees are immediately adjacent to the roadway (or in some instance actually encroach into it), the potential for an accident involving serious injury is greatly increased. Therefore, a clear (or recovery) zone is often an integral part of proper roadway design. The amount of space required in the zone is related directly to speed. In summary, trees can serve to beautify a roadway as well as cause the potential for serious accidents by either impeding sight or from errant vehicles striking them. The design engineer must use established guidelines, practices and standards when considering the layout of a driveway or intersection. These criteria are the minimum requirements which must be satisfied to ensure a proper design; it is encouraged that these minimum criteria be exceeded whenever possible. Although every attempt is made to preserve as many existing trees as possible, they must sometimes be removed if their location prevents fulfilling these requirements.
99 Turn Lanes Why are turn lanes used? Turn lanes at intersections are used primarily to separate turning traffic from through traffic. With turn lanes, vehicles waiting to turn are removed from the through lanes thereby reducing delay to through traffic. Turn lanes can also be used by vehicles as a deceleration area when leaving the major street. By removing turning vehicles from the through lane, turning lanes can also improve safety. Studies have shown that providing turn lanes for left-turning vehicles can reduce accidents by an average of 32.4 percent. Personal injury accidents involving left-turning vehicles can be decreased by as much as 50 percent. Intersection channelization projects have been shown to produce an average benefit/cost ratio of 2.31. Although, the treatment of right-turning vehicles is generally less critical than left- turning vehicles, separating right-turning vehicles from other traffic can significantly affect operations at an intersection. By adding a separate right-turn lane at a signalized intersection, the delay experienced by drivers on an approach can be reduced. At unsignalized intersections, right-turn lanes can serve to safely remove turning vehicles that are decelerating from the through traffic lanes. Turn lanes at major driveways can also improve efficiency and safety, especially on high volume or high speed roadways. When turn lanes are added, studies have shown a 52% decrease in rear-end accidents as well as 6% decrease in left- turn accidents.