Intersection Design and Channelization PDF

INTERSECTION DESIGN AND CHANNELIZATION By Dr. Vijay Kakade 1  INTRODUCTION General area where two/more roads join/cross including roadway and roadside facilities for traffic movements within the area Area is designated for the vehic...

INTERSECTION DESIGN AND CHANNELIZATION By Dr. Vijay Kakade 1  INTRODUCTION General area where two/more roads join/cross including roadway and roadside facilities for traffic movements within the area Area is designated for the vehicles to turn to different directions to reach their desired destinations 2 INTRODUCTION 3  INTRODUCTION Main function of intersection is to guide vehicles to their respective directions Traffic intersections are complex locations on any highway Drivers have to make split second decision at an intersection by considering his route, intersection geometry, speed and direction of other vehicles etc 4  INTRODUCTION Overall traffic flow depends on the performance of the intersections In urban areas intersection plays important role in accident prevention and total capacity of roadway 5 GENERAL DESIGN CONSIDERATIONS AND OBJECTIVES The main objective of the intersection design is to facilitate the convenience, ease and comfort of people traversing the intersection while enhancing the efficient movement The general design principles of intersection design are the approach speeds, restriction on available land, sight distance available and the presence of the larger volume of all the road users in urban areas 6  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Un Signalized Intersection 7  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Signalized Intersection 8  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Roundabouts 9  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Grade Separated Intersections 10  CLASSIFICATION OF INTERSECTIOS Types of Intersections Depending on Geometric Forms  3- Leg Intersection 11  CLASSIFICATION OF INTERSECTIOS Types of Intersections Depending on Geometric Forms  4- Leg Intersection 12  CLASSIFICATION OF INTERSECTIOS Types of Intersections Depending on Geometric Forms  Staggered Intersection 13  CLASSIFICATION OF INTERSECTIOS Types of Intersections Depending on Geometric Forms  Y- Intersection 14  CLASSIFICATION OF INTERSECTIOS Types of Intersections Depending on Geometric Forms  Multi- Leg Junction 15  CONFLICTS AT INTERSECTION Conflicts at an intersection are different for different types of intersection Intersection control measure adopted must be able to resolve the conflicts at intersection for safe and efficient movement of both vehicular traffic and pedestrians 16  CONFLICTS AT INTERSECTION Methods of intersection controls  Time Sharing: Widely seen on road intersections with traffic signals  Space Sharing: These intersections facilitates movement at different levels for vehicles and pedestrians 17  CONFLICTS AT INTERSECTION Type of intersection control adopted depend on  Traffic Volume  Road Geometry  Cost Involved  Importance of the Road 18  CONFLICTS AT INTERSECTION Conflicts at 3-Leg Intersection 19  CONFLICTS AT INTERSECTION Conflicts at 4-Leg Intersection 20  CONFLICTS AT INTERSECTION Conflicts at 4-Leg Intersection 21  CONFLICTS AT INTERSECTION Conflicts at Intersection 22  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Installation of Left Turn Lane  Help to reduce rear end crashes and red light running crashes  The addition of a left-turn lane increases capacity for the approach by removing left-turn movements from the through traffic stream 23  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Installation of Left Turn Lane  Provision of a left-turn lane in conjunction with protected left-turn phasing would appear to provide the most benefit 24  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Installation of Left Turn Lane  Types of Left Turn Phasing  Permissive: Vehicles are allowed to make a turn on circular green indication but must yield to opposite traffic  Exclusive: Vehicles are allowed to make a turn only on green arrow indication  Exclusive/Permissive: During a portion of the left- turn phase, the left-turn movement is made on a green arrow and is protected from opposing traffic. In addition, left turns may be made during the remaining green through phase when there are available gaps in opposing traffic 25  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Installation of Left Turn Lane  If a left-turn lane is excessively long, through drivers may enter the lane by mistake without realizing it is a left-turn lane  Effective signing and marking of the upstream end of the left-turn lane should be provided to avoid entry of through traffic into left-turn lane 26  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Installation of Left Turn Lane  For cases where widening is required to add a left-turn lane, the crossing distance and conflict area for pedestrians will increase  For wide roadway sections, pedestrian refuges should be provided 27  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Installation of Left Turn Lane  Part of the safety benefits of installing the turn lane may be lost due to a loss of shoulder, less proximity to roadside objects, and a reduction in intersection sight distance 28  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Installation of Left Turn Lane  The cost of construction and the accompanying signing and striping are one of the main economic disadvantages to installing a left-turn lane  Access to properties adjacent to the intersection approach may need to be restricted when a left-turn lane is installed 29  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Installation of Left Turn Lane 30  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Summary of Issues for Left Turn Lane 31  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Installation of Multiple Left Turn Lanes  Used at signalized intersections where traffic volumes have increased beyond the design volume of the original single left- turn lane  Multiple left-turn lanes allow for the allocation of green time to other critical movements or use of a shorter cycle length 32  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Installation of Multiple Left Turn Lanes  Dual left-turn lanes are generally considered when left-turn volumes exceed 300 vehicles per hour  A left-turn demand exceeding 600 vehicles per hour requires a triple left- turn lanes 33  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Installation of Multiple Left Turn Lanes  Multiple lanes are not appropriate where:  A high number of vehicle-pedestrian conflicts occur  Left-turning vehicles are not expected to evenly distribute themselves among the lanes  Channelization may be obscured  Sufficient right-of-way is not available to provide for the design vehicle 34  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Installation of Multiple Left Turn Lanes  Pavement markings can help eliminate driver confusion and eliminate vehicle conflict by channeling vehicles in their proper turn path  Prominent and well-placed signing should be used with dual and triple left-turn movements, especially in advance of the intersection 35  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Installation of Multiple Left Turn Lanes  The excess green time for left-turn movements resulting from the additional lane should be allocated to other critical movements or removed from the entire cycle to reduce the cycle length 36  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Installation of Multiple Left Turn Lanes  Common crash types in multiple turn lanes are sideswipes between vehicles in the turn lanes 37  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Installation of Multiple Left Turn Lanes  A study of double and triple left-turn lanes in Las Vegas, NV, showed that about 8 percent of intersection-related sideswipes occur at double lefts, and 50 percent at triple lefts  These sideswipes are 1.4 and 9.2 percent of all crashes at the intersections with double and triple lefts, respectively 38  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Installation of Multiple Left Turn Lanes  Turn path geometry and elimination of downstream bottlenecks are important considerations for reducing sideswipes 39  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Installation of Multiple Left Turn Lanes  Construction of triple left-turn lanes has not resulted in unexpected or unacceptable crash experiences  Accidents occurred in Triple left-turn lanes are angle crashes 40  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Installation of Multiple Left Turn Lanes  Crashes on three left-turn lanes are attributed to short clearance intervals and limited sight distance, not operation of the triple left  Public education of the proper use of triple left turns will be necessary where these are being considered at an intersection 41  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Installation of Multiple Left Turn Lanes Safety Benefits Associated with Double Left-Turn Lane 42  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Installation of Multiple Left Turn Lanes  Multiple left-turn lanes can improve intersection operations by reducing the time allocated to the signal phase for the left-turn movement  Triple left-turn lanes have been constructed to meet the left-turn capacity demand without having to construct an interchange 43  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Installation of Multiple Left Turn Lanes  Triple left-turn lanes can accommodate left-turn volumes of more than 600 vehicles per hour  Vehicle delays, intersection queues, and green time for the left-turn movement are all reduced, improving operation of the entire intersection 44  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Installation of Multiple Left Turn Lanes  Addition of turning lanes increases the crossing distance for pedestrians, as well as their exposure to potential conflicts if roadway widening is required  Right-of-way costs and access to adjacent properties are significant issues to consider 45  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Summary of Issues for Multiple Left Turn Lanes 46  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Addition of Right Turn Lane  Significant volumes of right-turning traffic can have an adverse effect on both intersection operations and safety  In addition to providing safety benefits for approaching vehicles, right-turn lanes at signalized intersections can be used to reduce vehicular delay and increase intersection capacity 47  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Addition of Right Turn Lane 48  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Addition of Right Turn Lane  Factors Considered for Deciding Need of Right Turn Lane  Vehicle speeds  Turning and through volumes  Percentage of trucks 49  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Addition of Right Turn Lane  Factors Considered for Deciding Need of Right Turn Lane  Approach capacity  Desire to provide right-turn-on-red operation  Type of highway 50  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Addition of Right Turn Lane  Factors Considered for Deciding Need of Right Turn Lane  Arrangement/frequency of intersections  Crash history involving right turns  Pedestrian conflicts  Available right-of-way 51  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Addition of Right Turn Lane Warrants for right-turn lanes on four-lane, high-speed roadways 52  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Addition of Right Turn Lane  Key design criteria for right turn lane are  Entering taper  Deceleration Length  Storage Length 53  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Addition of Right Turn Lane  Key design criteria for right turn lane are  Lane Width 54  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Addition of Right Turn Lane  Key design criteria for right turn lane are  Corner Radius  Sight Distance 55  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Addition of Right Turn Lane  Right-turn lanes are often used to prevent the undesirable effects resulting from the deceleration of turning vehicles  Vehicle traveling on an at-grade arterial at a speed 16 km/h (10 mph) slower than the speed of the normal traffic stream is 180 times more likely to be involved in a crash than a vehicle traveling at the normal traffic speed 56  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Addition of Right Turn Lane  Right-turn channelization has been shown to reduce right-turn angle crashes 57  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Addition of Right Turn Lane  The addition of a right-turn lane may result in an increase in sideswipe crashes 58  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Addition of Right Turn Lane  Larger curb radii produce higher vehicle speeds, but may negatively impact the safety of pedestrians and bicyclists  Provision of right-turn lanes minimizes collisions between vehicles turning right and following vehicles, particularly on high-volume and high-speed major roads 59  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Addition of Right Turn Lane  A right-turn lane may be appropriate in situations where there is an unusually high number of rear-end collisions on a particular approach  Installation of a right-turn lane on one major road approach at a signalized intersection is expected to reduce total crashes by 2.5 percent, and crashes are expected to decrease by 5 percent when right-turn lanes are constructed on both major-road approach 60  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Addition of Right Turn Lane Safety benefits associated with right turn improvements 61  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Addition of Right Turn Lane  Right-turn lanes will remove decelerating and slower-moving vehicles from the through traffic stream, which will reduce delay for following through vehicles  Vehicles in the right-turn lane may block the cross street drivers' view of through traffic 62  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Addition of Right Turn Lane 63  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Addition of Right Turn Lane  Restriping of right shoulder to provide a right turn lane may impact the safety due to decrease in distance to roadside objects  Effective signing and marking the upstream end of the right-turn lane should be done to avoid the entry of through vehicles 64  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Addition of Right Turn Lane  If access to a right-turn lane is blocked by a queue of through vehicles at a signal, drivers turning right may block the movement of through traffic if the two movements operate on separate phases  The speed of turning vehicles is a risk to pedestrian safety 65  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Addition of Right Turn Lane  The cost of construction (including relocation of signal equipment) and right-of-way acquisition is the main disadvantage to installation of a turn lane  Access to properties adjacent to the intersection approach may need to be restricted when a turn lane is installed 66  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Addition of Right Turn Lane  Periodic enforcement may be needed to prevent red-light violations, especially if right turns on red are prohibited 67  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Summary of Issues for Right Turn Lanes 68  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Summary of Issues for Right Turn Lanes Off-Tracking of Vehicle 69  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Addition of Double Right Turn Lane  Double right-turn lanes will be provided if there is high volume of right turning vehicles  It will increase capacity for the turns and reduce delay for other movements at the intersection  Double right-turn lanes can reduce both the length needed for turn lanes and the green time needed for that movement 70  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Addition of Double Right Turn Lane 71  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Addition of Double Right Turn Lane  Approaches with right-turn volumes that cannot be accommodated in a single turn lane without excessively long green times (and delays for other approaches) may be appropriate locations for double turn lanes  Locations where right-of-way is not available to provide a long turn lane but there is space for two shorter turn lanes may be ideal for double turn lanes 72  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Addition of Double Right Turn Lane  Additional deceleration and storage space will help in prevention of spillover into adjacent through lanes  A double turn lane will result in a wider footprint for the intersection and increase the distance pedestrians must cross 73  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Summary of Issues for Double Right Turn Lanes 74  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Channelized Right Turn Lane  Channelization of the right turn with a raised or painted island can provide larger turning radii and allow for higher turning speeds  It can also provide an area for pedestrian refuge 75  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Channelized Right Turn Lane 76  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Channelized Right Turn Lane  Channelized right-turn lanes are applicable for intersections with a high volume of right-turning vehicles that experience excessive delay due to the traffic signal  A channelized right-turn lane will have a larger footprint than an intersection with a conventional right-turn lane 77  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Channelized Right Turn Lane  Additional right-of-way may be needed to accommodate the larger corner radius  Raised islands have been found to be more effective than flush painted islands at reducing nighttime collisions 78  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Channelized Right Turn Lane Flush Painted Island Raised Island with Pedestrian Refuge Ar 79  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Channelized Right Turn Lane  A reduction in rear-end collisions involving right-turning vehicles and following through vehicles could be expected to reduce after construction of a right-turn roadway  Potential for rear-end and sideswipe crashes on the departure lanes may increase 80  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Channelized Right Turn Lane  Higher speeds and a possibly longer crossing distance and exposure could lead to an increase in crashes involving pedestrians, and the resulting crashes will likely have more serious consequences  Safety benefits associated with right- turn channelization 81  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Channelized Right Turn Lane  Through vehicles will experience less delay if right-turning vehicles do not have to decelerate in a through lane  More green time available to other movements at intersection by provision of right turn lane 82  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Channelized Right Turn Lane  Right-turn roadways can reduce the safety of pedestrian crossings if an area is not provided for pedestrian refuge  In areas with significant pedestrian traffic, consideration should be given to minimizing the curb radii while still accommodating the turning path of the design vehicle 83  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Channelized Right Turn Lane  Access to adjacent properties may need to be restricted to provide a merge area  Owners of adjacent property should be involved in early discussions regarding the plans 84  CONFLICTS AT INTERSECTION Minimization of Conflicts at Intersection  Summary of Issues for Channelized Right Turn Lanes 85  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Unsignalized Intersection  Provided where low volume road intersects high volume roads  It may be three or four leg intersection 86 Three Leg Intersection Four Leg Intersection  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Types of Unsignalized Intersection  Uncontrolled Intersection  YIELD Sign-Controlled Intersection  Stop Sign Controlled Intersection 87  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Types of Unsignalized Intersection  Uncontrolled Intersection  The entrance into the intersection from any of the approaches is not controlled by a regulatory sign or traffic signal  When two vehicles approach or enter an intersection from different highways at approximately the same time, the driver of the vehicle on the left shall yield the right-of-way to the vehicle on the right 88  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Types of Unsignalized Intersection  Uncontrolled Intersection 89  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Types of Unsignalized Intersection  Uncontrolled Intersection  The driver must also yield to any vehicle that is already lawfully in the intersection and any pedestrian in a marked or unmarked crosswalk  Uncontrolled intersections are usually limited to very low-volume roads in rural or residential neighbourhood 90  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Types of Unsignalized Intersection  Uncontrolled Intersection Residential Neighbourhood Very Low Volume, Rural Roads 91  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Types of Unsignalized Intersection  YIELD Sign Controlled Intersection  Entrance into the intersection from one or more of the approaches is controlled by a YIELD sign  Drivers on each approach controlled by a YIELD sign are required to reduce their speed to concede the right-of-way to vehicles and non-motorists in the intersection 92  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Types of Unsignalized Intersection  YIELD Sign Controlled Intersection  Adequate sight distance must be present so the driver approaching the YIELD sign can stop  YIELD signs are usually placed to control the minor road  Roundabouts and mini-roundabouts—represent the only intersections at which YIELD signs are installed on all approaches, as vehicles within the circular roadway always have the right-of-way https://www.youtube.com/watch?v=pTzWibBhSwg 93  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Types of Unsignalized Intersection  YIELD Sign Controlled Intersection Examples of YIELD Signs used as Intersection Control 94  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Types of Unsignalized Intersection  STOP Sign Controlled Intersection  Entrance into these intersections from one or more approaches is controlled by a STOP sign  Drivers are required to come to a full stop at the intersection and proceed only if there are no vehicles approaching from any of the uncontrolled approaches and there are no pedestrians in the intersection 95  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Types of Unsignalized Intersection  STOP Sign Controlled Intersection  Minor-road-only stop control—at intersections having at least one approach (typically, the lower-volume, minor road) under the control of a STOP sign and at least one approach not controlled by a STOP sign  Multi-way stop control—at intersections where all approaches are controlled by a STOP sign and an ALL WAY supplemental plaque is used 96  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Types of Unsignalized Intersection  STOP Sign Controlled Intersection  Multi-way stop control— the right-of-way is determined by the order in which users reach the intersection; if two vehicles arrive at the intersection at nearly the same time, then the vehicle on the right has the right- of-way top Sign at a minor road approach ALL of WAY supplemented plaque at multi 97 leg intersection Stop controlled intersection  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Circular Intersection  U-Turn-Centered Intersection 98  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Circular Intersection  At-grade intersection at which vehicles travel counterclockwise around a central island and exit to an intersecting road  Design is intended to compel drivers to decrease their speeds approaching and within the intersection 99  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Types of Circular Intersection  Roundabout  Mini-Roundabout  Residential Traffic Circle 100  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Roundabout  At a roundabout, traffic travels counterclockwise around a central raised island, and entering traffic must yield to circulating traffic 101  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Roundabout 102  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Central Island  A non-traversable inner island  Central Island should be always raised  Central island should be circular in shape  Oval or irregular shape inner island can be used 103  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Central Island Roundabout with Oval Island Roundabout with Irregular Island 104  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Central Island  One or more circulating lanes  Inscribed Circulating diameter range 105  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Splitter Island  Also called separator islands or median islands  Should be provided on all roundabouts, except those with very small diameters 106  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Splitter Island  Provide shelter for pedestrians (including wheelchairs, bicycles, and baby strollers), assist in controlling speeds, guide traffic into the roundabout, physically separate entering and exiting traffic streams, and deter wrong-way movements  Can be used as a place for mounting signs 107  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Splitter Island 108  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Splitter Island  The total length of the island should generally be at least 15 m  larger splitter islands can help reduce confusion for entering motorists  Increasing the width of the splitter islands generally requires increasing the inscribed circle diameter 109  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Entry Width  The entry capacity increases steadily with incremental increases to the entry width  Entry width is measured from the point where the yield line intersects the left edge of the traveled-way to the right edge of the traveledway, along a line perpendicular to the right curb line 110  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Entry Width 111  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Entry Width  To maximize the roundabout’s safety, entry widths should be kept to a minimum  Entry widths for single-lane entrances range from 4.3 to 5.5 m  Values higher or lower than this range may be required for site-specific design vehicle and speed requirements for critical vehicle paths 112  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Entry Width  When the capacity requirements can only be met by increasing the entry width, this can be done in two ways 113  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Circulatory Roadway Width  The required width of the circulatory roadway is determined from the width of the entries and the turning requirements of the design vehicle  It should always be at least as wide as the maximum entry width and remain constant throughout the roundabout 114  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Circulatory Roadway Width 115  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Circulatory Roadway Width  For single lane roundabout, circulatory roadway width ranges from 4.9 m to 6.1 m  Too wide circulatory roadway width should not be provided for single roundabout 116  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Circulatory Roadway Width  At double-lane roundabouts, the circulatory roadway width is not governed by the design vehicle  The width requirement for double lane roundabout depend on number of lanes at the widest entry 117  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Circulatory Roadway Width  The combination of vehicle types to be accommodated side-by-side is dependent upon the specific traffic conditions at each site 118  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Circulatory Roadway Width 119  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Entry Curves  The entry curves are the set of one or more curves along the right curb (or edge of pavement) of the entry roadway leading into the circulatory roadway  The entry radius, in conjunction with the entry width, the circulatory roadway width, and the central island geometry, controls the amount of deflection imposed on a vehicle’s entry path 120  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Entry Curves 121  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Entry Curves  Larger entry radii produce faster entry speeds  The capacity of an entry increases as its entry radius is increased (up to 20 m), beyond which entry radius has little effect on capacity 122  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Entry Curves  Design speed is important factor in deciding the radius of entry curve  Entry radii at urban single-lane roundabouts typically ranges from 10 to 30 m 123  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Entry Curves  Excessive entry speed if larger entry radii used  At local street roundabouts, entry radii may be below 10 m if the design vehicle is small  At double-lane roundabouts, the design of the entry curvature is more complicated 124  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Entry Curves  On double lane entries, curve radii ranges from 30 to 60 m in urban area and 40 to 80 m in rural area 125  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Entry Curves  Design Methods to avoid overlap on double lane entries 126  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Entry Curves  Design Methods to avoid overlap on double lane entries 127  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Exit Curves  Exit curves usually have larger radii than entry curves  The exit path radius should not be significantly greater than the circulating path radius  The exit curve is designed to be curvilinearly tangential to the outside edge of the circulatory roadway 128  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Exit Curves Single Lane Roundabout Exit Design 129  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Exit Curves  At single lane roundabout in urban area, exit radius should be selected such way that vehicle speed at design curve remains below 40 km/h  Exit radii should be no less than 15 m  At locations with pedestrian activity and no large semi-trailer traffic, exit radii may be as low as 10 to 12 m 130  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Exit Curves  Low exit radii should only be used in conjunction with similar or smaller entry radii on urban compact roundabouts with inscribed circle diameters below 35 m  In rural areas exit curves may be designed with large radii  Pedestrian activity be considered at all exits except where separate pedestrian facilities (paths, etc.) or other restrictions eliminate the likelihood of pedestrian activity in the foreseeable future 131  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Roundabout: Exit Curves  Exit radius at a double-lane roundabout not be too small  Selected radii should be able to reduce the design speed below 40 km/h 132  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Rural Roundabout  Roundabouts located on rural roads have special design considerations  Primary safety concern in rural locations is to make drivers aware of the roundabout with ample distance 133  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Rural Roundabout: Visibility  The geometric alignment of approach roadways should be constructed to maximize the visibility of the central island and the general shape of the roundabout  Where adequate visibility cannot be provided solely through geometric alignment, additional treatments (signing, pavement markings, advanced warning beacons, etc.) should be considered 134  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Rural Roundabout: Curbing  Rural highways typically have no outside curbs  Narrow shoulder widths and curbs on the outside edges of pavement give drivers a sense they are entering a more urbanized setting  Reduce a shoulder width and introduce a curbs when installing a roundabout on an open rural highway 135  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Rural Roundabout: Curbing  Curbs help to improve delineation and to prevent “corner cutting”  Curbs help to confine vehicles to the intended design path  It is desirable to extend the curbing from the approach for at least the length of the required deceleration distance to the roundabout 136  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Rural Roundabout: Splitter Island  Longer splitter islands on the approaches help to reduce the speed  Splitter islands should generally be extended upstream of the yield bar to the point at which entering drivers are expected to begin decelerating comfortably 137  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Rural Roundabout: Splitter Island 138  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Rural Roundabout: Approach Curves  Roundabouts on high-speed roads (speeds of 80 km/h or higher), despite extra signing efforts, may not be expected by approaching drivers  Decreasing the radius of an approach curve generally decreases the approaching rear-end vehicle crash rate and the entering-circulating and exiting-circulating vehicle crash rates 139  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Rural Roundabout: Approach Curves  Decreasing the radius of an approach curve may increase sideswipe crash rates on the approach curve  Use of successive curves on approaches reduces the crashes 140  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Rural Roundabout: Approach Curves 141  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Rural Roundabout: Approach Curves  Equation to Estimate the Operating Speed of Two-Lane Rural Roads as a function of Degree of Curvature 142  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Key Design Elements of Rural Roundabout: Approach Curves  Equation to Estimate the Operating Speed of Four-Lane Rural Roads as a function of Degree of Curvature 143  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Mini Roundabout  Mini-roundabouts are generally used on lower- volume streets and where space is inadequate for a full-size roundabout  Mini roundabouts are a form of roundabout intersection and it is not a traffic calming https://www.youtube.com/watch? device v=fUFmuf_HRDg 144  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Mini Roundabout 145  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Mini Roundabout  Mini roundabouts should only be considered in areas where all approaching roadways have an 85th-percentile speed of less than 50 km/h  Mini roundabouts are not recommended in locations in which high U-turn traffic is expected 146  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Mini Roundabout  Mini roundabouts are not well suited for high volumes of trucks  Mini roundabouts are distinguished from neighbourhood traffic circles primarily by their traversable islands and yield control on all approaches 147  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Mini Roundabout  Generally do not include raised channelization to guide approaching traffic into the circulatory roadway  Design of mini roundabouts generally aligns passenger cars on the approach in such a way as to naturally follow the circulatory roadway and minimize running over the central island to the extent possible 148  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Mini Roundabout  Due to the small footprint, large vehicles are typically required to over-run the fully traversable central island 149  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Benefits of Mini Roundabout  Compact Size  Operational Efficiency  Traffic Safety  Traffic Calming 150  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  User Considerations in Planning and Design of Mini Roundabout  Motorists Mini roundabouts can enhance the safety for drivers including older drivers Allowing more time to make decisions, act, and react 151  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  User Considerations in Planning and Design of Mini Roundabout  Motorists Reducing the number of directions in which a driver needs to watch for conflicting traffic Reducing the need to judge gaps in fast traffic accurately 152  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  User Considerations in Planning and Design of Mini Roundabout  Pedestrians Pedestrians are accommodated at pedestrian crosswalks around the perimeter of the mini roundabout The splitter islands at mini-roundabouts typically do not provide the same degree of refuge as those at other roundabouts 153  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  User Considerations in Planning and Design of Mini Roundabout  Bicycles Mini roundabouts are located where bicyclists are comfortable to negotiate the roundabout as a motor vehicle If bicyclists desire to negotiate the intersection as a pedestrian, sidewalks and crosswalks are provided 154  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Location Considerations for Mini Roundabout  Space-constrained locations with reasonable approach speeds (50 km/h or less)  Residential environments  Intersections with high delay 155  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Operational Analysis for Mini Roundabout  Mini roundabouts are generally recommended for intersections in which the total entering daily traffic volume is no more than approximately 15,000 vehicles  Mini-roundabout may perform acceptably at higher volume locations 156  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Horizontal Design  Size: A mini roundabout is often considered as an alternative to a larger, single-lane roundabout Mini roundabouts should be made as large as possible within the intersection constraints 157  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Horizontal Design  Size: Mini-roundabout inscribed circle diameter generally should not exceed 30 m Roundabout to be provided if inscribed circle diameter requires more than 30 m 158  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Horizontal Design  Design Vehicle: The location and size of a mini-roundabout central island is dictated primarily by passenger car swept path requirements Island location should be at the center of the left-turning inner swept paths which will be near, but not necessarily on, the center of the inscribed circle 159  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Horizontal Design  Design Vehicle: Off-tracking of a large design vehicle should be accommodated by the footprint of the central island Passenger cars should be able to navigate through the intersection without being required to overrun the central island 160  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Horizontal Design  Design Speed : Vehicles should be able to pass through the intersection at reduced speed 161  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Horizontal Design  Central Island: The central island is typically fully traversable and may either be domed or raised with a mountable curb and flat top for larger islands A maximum height of island will be 12 cm 162  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Horizontal Design  Placement of Entrance Line: Incorrect placement can introduce undesirable driver behavior 163  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Horizontal Design  Placement of Entrance Line: 164  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Horizontal Design  Placement of Entrance Line: 165  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Horizontal Design  Placement of Entrance Line: 166  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Horizontal Design  Splitter Island: Used to align vehicles, to encourage deflection and proper circulation, and to provide pedestrian refuge Splitter islands are raised, mountable, or flush 167  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Horizontal Design  Splitter Island: Generally raised island preferred over flush island Due to narrow approach if it is not possible to provide the splitter island of required length, then provide it between entrance line and crosswalk 168  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Horizontal Design  Guidelines for Selection of Type of Splitter Island: Provide raised island if one or more following condition exist: 1. All design vehicles can navigate the roundabout without tracking over the splitter island area 2. Sufficient space is available to provide an island with a minimum area of 50 ft2 (4.6 m2) 3. Pedestrians are present at the intersection with regular frequency 169  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Horizontal Design  Guidelines for Selection of Type of Splitter Island: Provide Mountable island if one or more following condition exist: 1. Some design vehicles must travel over the splitter island area and truck volumes are minor 2. Sufficient space is available to provide an island with a minimum area of 50 ft2 (4.6 m2) 170  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Horizontal Design  Guidelines for Selection of Type of Splitter Island: Provide Flush (Painted) if one or more following condition exist: 1. Vehicles are expected to travel over the splitter island area with relative frequency to navigate the intersection 2. An island with a minimum area of 50 ft 2 (4.6 m2) can not be achieved 3. The approach has low vehicle speeds (preferably no more than 40 km/h 171  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Horizontal Design  Splitter Island: 172  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Horizontal Design  Splitter Island: Raised Splitter Island 173  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Pedestrian Design Treatments  The pedestrian crossing is recommended to be located 6.1 to 7.6 m upstream of the entrance line to accommodate one vehicle queue ahead of the crossing  Where a mountable or raised splitter island is used, the walkway through the splitter island should be “cut-through” instead of ramped 174  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Pedestrian Design Treatments  The cut-through walkway should be minimum of 3 m width  Sidewalk ramps should be provided to connect to the sidewalks at each end of the crosswalk 175  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Pedestrian Design Treatments 176 Sidewalk Ramp  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Pedestrian Design Treatments  Where a minimum splitter island width of 1.8 m is available on the approach, a pedestrian refuge can be provided within the splitter island  If refuge area not provided due to insufficient roadway width, the pedestrian need to cross in one stage 177  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Bicycle Design Treatments  The speeds of vehicles approaching and traveling through mini roundabouts are similar to those of bicyclists  Bicyclists are encouraged to navigate through a mini-roundabout as if they were a vehicle 178  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Bicycle Design Treatments  Where bicycle lanes are provided on the approaches to a mini-roundabout, they should be terminated 179  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Vertical Design  Mini-roundabouts should generally be designed to be outward draining  Outward sloping is recommended because it 1. Promotes safety 180  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Vertical Design  Outward sloping is recommended because it 2. Promotes lower circulation speeds 3. Minimizes breaks in the cross slopes of the entrance and exit lanes 4. Drains surface water to the outside of the roundabout 181  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Vertical Design  In most retrofit situations, installation of a mini-roundabout would not necessarily require significant grade modifications to the intersection 182  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Pavement Markings and Signs  Pavement markings and signs help to guide and regulate road users  Simple as compared to other types of roundabouts 183  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Pavement Markings  Pavement markings for mini-roundabouts are largely similar to those for other roundabouts  Additional pavement markings can be used to improve the visibility of direction of circulation and splitter islands 184  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Pavement Markings 185  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection 186  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Pavement Signs  Do not provide any sign within fully mountable central island  Provide circular intersection warning sign on each approach in advance of the YIELD Sign 187  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Pavement Signs 188  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Design Considerations for Mini Roundabout: Pavement Signs  Place YIELD signs as close to as practical to entrance line 189  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Residential Traffic Circle  Used at the intersection of two local residential streets for the purpose of traffic calming or aesthetic appeal  The approaches may be uncontrolled or controlled by a YIELD sign  Central island may or may not be traversable 190  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  Residential Traffic Circle  Unless explicitly prohibited, left-turning movements for larger vehicles are allowed to occur in front of the central island 191  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  U -Turn-Centered Intersection  Only restricted crossing U turn (RCUT) is applicable to unsignalized intersection  The RCUT incorporates directional left-turn crossovers at the intersection and U-turn crossovers upstream and downstream of the intersection 192  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  U -Turn-Centered Intersection RCUT for 4-legged Intersection RCUT for 3-legged Intersection 193  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  U -Turn-Centered Intersection  Minor street drivers desiring to turn left or continue straight must first turn right onto the major street, proceed to the downstream U-turn crossover, and execute a U-turn 194  CLASSIFICATION OF INTERSECTIOS Three main types of Intersection Designs  Nontraditional Types of Unsignalized Intersection  U -Turn-Centered Intersection  The crossovers and minor street right turns may be placed under the control of a STOP sign or a YIELD sign Intersection with RCU 195  CLASSIFICATION OF INTERSECTIOS Traffic Operations at Roundabout 196  CLASSIFICATION OF INTERSECTIOS Capacity of Roundabout 197  CLASSIFICATION OF INTERSECTIOS Capacity of Roundabout  Width of weaving is given by Where e1: width of carriageway at the entry e2: width of carriageway at the exit 198  CLASSIFICATION OF INTERSECTIOS Capacity of Roundabout  Weaving length determines how smoothly the traffic can merge and diverge  Weaving length depends on weaving width, proportion of weaving traffic to the non-weaving traffic  High ratio of weaving length to weaving width help in smooth merging 199 and diverging of traffic  CLASSIFICATION OF INTERSECTIOS Capacity of Roundabout  A ratio of 4 is the minimum value suggested by IRC  Very large weaving length is also dangerous  The capacity of rotary is determined by the capacity of each weaving section 200  CLASSIFICATION OF INTERSECTIOS Capacity of Roundabout where e = average entry and exit width = (e1+e2)/2 w = weaving width l = length of weaving p = proportion of weaving traffic to the non weaving traffic 201  CLASSIFICATION OF INTERSECTIOS Capacity of Roundabout Weaving Operations at Traffic Operation in a Rotar Intersection 202  CLASSIFICATION OF INTERSECTIOS Capacity of Roundabout  Capacity formula is valid if following conditions are satisfied  Weaving width at the rotary is in between 6 and 18 meters  The ratio of average width of the carriage way at entry and exit to the weaving width is in the range of 0.4 to 1 203  CLASSIFICATION OF INTERSECTIOS Capacity of Roundabout  Capacity formula is valid if following conditions are satisfied  The ratio of weaving width to weaving length of the roundabout is in between 0.12 and 0.4  The proportion of weaving traffic to non-weaving traffic in the rotary is in the range of 0.4 and 1  The weaving length available at the 204  Capacity of Roundabout Problem 1 The width of a carriage way approaching an intersection is given as 15 m. The entry and exit width at the rotary is 10 m. The traffic approaching the intersection from the four sides is shown in the figure below. Find the capacity of the rotary using the given data. 205  CLASSIFICATION OF INTERSECTIOS Problem 1 206  CLASSIFICATION OF INTERSECTIOS Answer 207  CLASSIFICATION OF INTERSECTIOS Answer 208  CLASSIFICATION OF INTERSECTIOS Answer Weaving width = ((e1+e2)/2) + 3.5= ((10+10)/2)+3.5 = 13.5 m Weaving length = 4*w = 4*13.5 = 54 m 209  CLASSIFICATION OF INTERSECTIOS Answer Proportion of weaving to non weaving traffic is highest in east-south direction = 3890 veh/hr 210  Capacity of Roundabout Problem 2 The width of a carriage way approaching an intersection is given as 12 m. The entry and exit width at the rotary is 8 m. The traffic approaching the intersection from the four sides is shown in the figure below. Find the capacity of the rotary using the given data. 211  Capacity of Roundabout Problem 2 212 Capacity of Roundabout Answer 213  Capacity of Roundabout Answer 214  Capacity of Roundabout Answer Weaving width = ((e1+e2)/2) + 3.5= ((8+8)/2)+3.5 = 11.5 m Weaving length = 4*w = 4*11.5 = 46 m 215  Capacity of Roundabout Answer Proportion of weaving to non weaving traffic is highest in east-south direction = 3136 veh/hr 216  SIGNALIZED INTERSECTION Points to be considered in the Geometric Design of Signalized Intersection  Principles of channelization  Number of intersection approaches  Intersection angle  Horizontal and vertical alignment  Corner radius and curb ramp design  Detectable warnings 217  SIGNALIZED INTERSECTION Points to be considered in the Geometric Design of Signalized Intersection  Access control  Sight distance  Pedestrian facilities  Bicycle facilities 218  SIGNALIZED INTERSECTION Principles of channelization  Basic principles of intersection channelization that can be applied to reduce conflicts are as follows  Discourage undesirable movements  Prevent left turns from driveways or minor streets based on safety or operational concerns  Design channelization to prevent wrong way movements onto freeway ramps, one- way streets, or divided roadways 219  SIGNALIZED INTERSECTION Principles of channelization  Basic principles of intersection channelization that can be applied to reduce conflicts are as follows  Discourage undesirable movements 220  SIGNALIZED INTERSECTION Principles of channelization  Basic principles of intersection channelization that can be applied to reduce conflicts are as follows  Define desirable paths for vehicles  The approach alignment to an intersection as well as the intersection itself should present the roadway user with a clear definition of the proper vehicle path  Clear definition of vehicle paths can minimize lane changing and avoid “trapping” vehicles in the incorrect lane 221  SIGNALIZED INTERSECTION Principles of channelization  Basic principles of intersection channelization that can be applied to reduce conflicts are as follows  Define desirable paths for vehicles 222  SIGNALIZED INTERSECTION Principles of channelization  Basic principles of intersection channelization that can be applied to reduce conflicts are as follows  Encourage safe speeds through design 223  SIGNALIZED INTERSECTION Principles of channelization  Basic principles of intersection channelization that can be applied to reduce conflicts are as follows  Separate points of conflict where possible 224  SIGNALIZED INTERSECTION Principles of channelization  Basic principles of intersection channelization that can be applied to reduce conflicts are as follows  Facilitate the movement of high- priority traffic flows 225  SIGNALIZED INTERSECTION Principles of channelization  Basic principles of intersection channelization that can be applied to reduce conflicts are as follows  Design approaches to intersect at near right angles and merge at flat angles 226  SIGNALIZED INTERSECTION Principles of channelization  Basic principles of intersection channelization that can be applied to reduce conflicts are as follows  Facilitate the desired scheme of traffic control  Lane arrangements, location of channelization islands, and medians should be established  Provision of exclusive left-turn bays  Prohibit U-Turn if insufficient width is available  Provision of Reversible Lanes for arterial roads 227  SIGNALIZED INTERSECTION Principles of channelization  Basic principles of intersection channelization that can be applied to reduce conflicts are as follows  Accommodate decelerating, slow, or stopped vehicles outside higher speed through traffic lanes  Speed differentials between vehicles in the traffic stream are a primary cause of traffic crashes  Speed differentials at intersections are inherent  Provision of exclusive left- and right-turn lanes 228  SIGNALIZED INTERSECTION Principles of channelization  Basic principles of intersection channelization that can be applied to reduce conflicts are as follows  Provide safe refuge and wayfinding for bicyclists and pedestrians  Intersection design must consider the needs of roadway users other than motorists  The use of raised medians, traffic islands, and other pedestrian-friendly treatments should be considered as part of the design process 229  SIGNALIZED INTERSECTION Principles of channelization  Basic principles of intersection channelization that can be applied to reduce conflicts are as follows  Provide safe refuge and wayfinding for bicyclists and pedestrians 230  SIGNALIZED INTERSECTION Number Of Intersection Legs  The complexity of an intersection increases with an increasing number of approach legs to the intersections  At many potential conflicts, including crossing and merging conflicts, can be managed (but not eliminated) at a signalized intersection by separating conflicts in time 231  SIGNALIZED INTERSECTION Intersection Angle  The angle of intersection of two roadways can influence both the safety and operational characteristics of an intersection  Heavily skewed intersections produce larger, open pavement areas 232  SIGNALIZED INTERSECTION Intersection Angle  Undesirable operational and safety characteristics of skewed intersections include:  Vehicles crossing the intersection are more exposed to conflicts  Pedestrians and bicyclists are exposed to vehicular traffic longer  Pedestrians with visual disabilities may have difficulty  Driver confusion may result at skewed crossings 233  SIGNALIZED INTERSECTION Intersection Angle  Skewed intersections are generally experiences right-angle type crashes  Skewed intersections below 60° are not permitted (As per AASHTO)  Intersection angles of 90 degrees for new intersections where right-of-way is not a constraint (FHWA) 234  SIGNALIZED INTERSECTION Intersection Angle  Angles of not less than 75 degrees for new facilities or redesigns of existing facilities where right-of- way is restricted (FHWA) 235  SIGNALIZED INTERSECTION Horizontal And Vertical Alignment  The approach to a signalized intersection should promote awareness of an intersection by providing the required stopping sight distance in advance of the intersection  Avoid approach grades to an intersection of greater than 6 percent 236  SIGNALIZED INTERSECTION Horizontal And Vertical Alignment  On higher design speed facilities (80 km/h and greater), a maximum grade of 3 percent should be considered  Avoid locating intersections along a horizontal curve of the intersecting road 237  SIGNALIZED INTERSECTION Corner Radius And Curb Ramp Design  Selection of corner radius and curb ramp design depends on pedestrian crossing and design vehicle needs at intersection  Provide a pedestrian crossing perpendicular to the traffic flow 238  SIGNALIZED INTERSECTION Corner Radius And Curb Ramp Design  Do not keep intermediate angle point in pedestrian crossing  Corner radii should also be designed to accommodate the turning path of a design vehicle 239  SIGNALIZED INTERSECTION Corner Radius And Curb Ramp Design  Corner Radius  The corner radii of an intersection should be designed to facilitate the turning and tracking requirements of the selected design vehicle  Corner radii should be compatible with other intersection features and the speed environment 240  SIGNALIZED INTERSECTION Corner Radius And Curb Ramp Design  Factors Influencing Selection of Corner Radius  Design vehicle: Largest vehicle type that will regularly use an intersection  Angle of intersection: Large intersection skew angles make turning maneuvers more difficult for larger vehicles 241  SIGNALIZED INTERSECTION Corner Radius And Curb Ramp Design  Factors Influencing Selection of Corner Radius  Pedestrians and bicyclists: Use smaller radii in areas of high pedestrian and bike traffic  Constraints: Multicentered curves or simple curves with tangent offsets can be used to match the turn path of the design vehicle and reduce required right-of-way 242  SIGNALIZED INTERSECTION Corner Radius And Curb Ramp Design  Factors Influencing Selection of Corner Radius  Encroachment: Must consider whether a turning vehicle's wheel path or swept path should not encroach into adjacent lanes (same direction), flush islands that separate traffic, or even into opposing lanes  Intersection size: Corner radius influences the overall width of the intersection 243  SIGNALIZED INTERSECTION Corner Radius And Curb Ramp Design Curb R