roundabout ~' ~ design guidelines - Institute of Transportation ...

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2.0 USE OF ROUNDABOUTS 2.1 GENERAL Roundabouts should be considered at a wide range of intersection types including but not limited to; freeway terminal interchanges, state route intersections, and state route/local route intersections. Roundabouts perform better at intersections with roughly similar traffic volumes and at intersections with heavy left turning movements. Roundabouts can improve safety by simplifying conflicts, reducing vehicle speeds and providing a clearer indication of the driver’s right-of-way compared to other forms of intersection control. 2.2 SITE SELECTION CRITERIA The following site selection guidelines are intended as general guidelines only. The designer should determine the applicability of a roundabout at a particular intersection by considering the following items: - Capacity Analysis of all methods under consideration - Cost/Benefit Analysis - Percentage of Truck Traffic - Bicycle and Pedestrian Traffic - Right-of-Way Consideration - Parking Requirements - Compatibility with Adjacent Intersection - Safety Aspects - Effect of Possible Traffic Growth - Speed of Traffic - Installation and Maintenance Costs ROUNDABOUT SHORTLISTING GUIDELINES Introduction The following guidelines are based on existing design manuals from England, Australia, and other countries, and video tapes of existing roundabouts. The guidelines are not meant to be rigid but should be used in conjunction with engineering judgement, and traffic analysis. For example, it could be stated that a roundabout should not be placed where there is an existing signal in close proximity (i.e. Chevy Chase Circle) because the queues from the signal may extend temporarily into the roundabout. Intuitively, this would not seem to be an appropriate place for a roundabout, however traffic analysis may indicate that a roundabout may work better than any other solution. The proposed intersection treatment, therefore, should be chosen based on the advantages/8disadvantages, benefits/costs that it provides. . 3
Location l High Accident Location (with left turn or right angle accidents) 0 Capacity/Delay Problem Intersection l l Intersection in which traffic signal was requested but not warranted. 4-Way Stops Traffic Volume and Composition l Heavy Delay on Side Street l Flow Distribution with Heavy Left Turn Movement (makes signals less efficient -no impact on roundabout) 0 DHV of 7000 or Less (initially) Right-of-Wav l Generally take no more right-of-way than comparable solution using signals: Appropriate Sites for Roundabouts 0 0 0 0 0 0 0 0 0 0 Heavy delay on minor road. Traffic signals result in greater delay. Intersection with heavy left turning traffic. Intersection with more than four legs or unusual geometry. At rural intersections (including those in high speed areas) at which there is an accident involving crossing traffic. Where major roads intersect at “Y” or “T” junctions. At locations where traffic growth is expected to be high and where future traffic patterns are uncertain or changeable. At intersections where U-turns are desirable. At Freeway Interchange Ramps. High accident intersection where right angle accidents are prominent. 4
Page 1 and 2: ROUNDABOUT ~’ ~ DESIGN GUIDELINES
Page 3 and 4: Figure 1.1 Figure 3.1 Figure 3.2 Fi
Page 5 and 6: FORWARD The mission of the Maryland
Page 7: Deflection is the physical slowing
Page 11 and 12: 3.0 PERFORMANCE OF ROUNDABOUTS 3.1
Page 13 and 14: L FIGURE 3. I Typical turning movem
Page 15 and 16: NOTE: For some circulating roadways
Page 17 and 18: Number of circulating lanes one mor
Page 19 and 20: Number of circulating lanes Number
Page 21 and 22: TABLE 3.5 Average headway between b
Page 23 and 24: 2500 2000 Entry $P$c~y 1500 Both la
Page 25 and 26: 3.4 Delays at Roundabouts -. There
Page 27 and 28: Negotiated speed through roundabout
Page 29 and 30: 3.4.2 Geometric Delay The geometric
Page 31 and 32: at negotiation speed “, mph ~~~~~
Page 33 and 34: The safety record of roundabouts wi
Page 35 and 36: circulating traffic and the right t
Page 37 and 38: 4 GEOMETRIC DESIGN OF ROUNDABOUTS 4
Page 39 and 40: 4.1.4 INSCRIBED CIRCLE DIAMETER The
Page 41 and 42: 4.1.7 DEFLECTION Adequate deflectio
Page 43 and 44: a) By Central Island I) Wlthout ‘
Page 45 and 46: Table 4.1 indicates the required ap
Page 47 and 48: To enhance the prominence of the ro
Page 49 and 50: In these situations the central isl
Page 51 and 52: L FIGURE 5.1 Ekampte of the use of
Page 53 and 54: /-LANDSCAPED CENTRAL 1 ISLAND CONCR
Page 55 and 56: 3. Exit Guide signs should be used.
Page 57 and 58: l OPTIONAL FIGURE 6.2 Typical signi
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a”-16” BROKEN WHITE 8” SOLID
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8.0 PEDESTRIAN AND BICYCLE CONSIDER
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PAVED SIDEWALK \ PAVED SIDEWALK -/
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9.0 WORK ZONE TRAFFIC CONTROL Durin
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WORK ZONE TRAFFIC COMROL lYPICAL IM
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v\ 00 00 0 0 000 (IONE- R6-I R R4-7
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BENEFIT/COST ANALYSIS 1. Accident d
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REFERENCES 1. 2. 3. 4. 5. 6. 7. 8.
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