National Academies Press: OpenBook

Safety of U-Turns at Unsignalized Median Openings (2004)

Chapter: Appendix B - Summary of Survey Responses From State and Local Highway Agencies

« Previous: Appendix A - Highway Agency Survey Questionnaire
Page 90
Suggested Citation:"Appendix B - Summary of Survey Responses From State and Local Highway Agencies." National Academies of Sciences, Engineering, and Medicine. 2004. Safety of U-Turns at Unsignalized Median Openings. Washington, DC: The National Academies Press. doi: 10.17226/13768.
×
Page 90
Page 91
Suggested Citation:"Appendix B - Summary of Survey Responses From State and Local Highway Agencies." National Academies of Sciences, Engineering, and Medicine. 2004. Safety of U-Turns at Unsignalized Median Openings. Washington, DC: The National Academies Press. doi: 10.17226/13768.
×
Page 91
Page 92
Suggested Citation:"Appendix B - Summary of Survey Responses From State and Local Highway Agencies." National Academies of Sciences, Engineering, and Medicine. 2004. Safety of U-Turns at Unsignalized Median Openings. Washington, DC: The National Academies Press. doi: 10.17226/13768.
×
Page 92
Page 93
Suggested Citation:"Appendix B - Summary of Survey Responses From State and Local Highway Agencies." National Academies of Sciences, Engineering, and Medicine. 2004. Safety of U-Turns at Unsignalized Median Openings. Washington, DC: The National Academies Press. doi: 10.17226/13768.
×
Page 93
Page 94
Suggested Citation:"Appendix B - Summary of Survey Responses From State and Local Highway Agencies." National Academies of Sciences, Engineering, and Medicine. 2004. Safety of U-Turns at Unsignalized Median Openings. Washington, DC: The National Academies Press. doi: 10.17226/13768.
×
Page 94
Page 95
Suggested Citation:"Appendix B - Summary of Survey Responses From State and Local Highway Agencies." National Academies of Sciences, Engineering, and Medicine. 2004. Safety of U-Turns at Unsignalized Median Openings. Washington, DC: The National Academies Press. doi: 10.17226/13768.
×
Page 95
Page 96
Suggested Citation:"Appendix B - Summary of Survey Responses From State and Local Highway Agencies." National Academies of Sciences, Engineering, and Medicine. 2004. Safety of U-Turns at Unsignalized Median Openings. Washington, DC: The National Academies Press. doi: 10.17226/13768.
×
Page 96
Page 97
Suggested Citation:"Appendix B - Summary of Survey Responses From State and Local Highway Agencies." National Academies of Sciences, Engineering, and Medicine. 2004. Safety of U-Turns at Unsignalized Median Openings. Washington, DC: The National Academies Press. doi: 10.17226/13768.
×
Page 97
Page 98
Suggested Citation:"Appendix B - Summary of Survey Responses From State and Local Highway Agencies." National Academies of Sciences, Engineering, and Medicine. 2004. Safety of U-Turns at Unsignalized Median Openings. Washington, DC: The National Academies Press. doi: 10.17226/13768.
×
Page 98
Page 99
Suggested Citation:"Appendix B - Summary of Survey Responses From State and Local Highway Agencies." National Academies of Sciences, Engineering, and Medicine. 2004. Safety of U-Turns at Unsignalized Median Openings. Washington, DC: The National Academies Press. doi: 10.17226/13768.
×
Page 99
Page 100
Suggested Citation:"Appendix B - Summary of Survey Responses From State and Local Highway Agencies." National Academies of Sciences, Engineering, and Medicine. 2004. Safety of U-Turns at Unsignalized Median Openings. Washington, DC: The National Academies Press. doi: 10.17226/13768.
×
Page 100
Page 101
Suggested Citation:"Appendix B - Summary of Survey Responses From State and Local Highway Agencies." National Academies of Sciences, Engineering, and Medicine. 2004. Safety of U-Turns at Unsignalized Median Openings. Washington, DC: The National Academies Press. doi: 10.17226/13768.
×
Page 101
Page 102
Suggested Citation:"Appendix B - Summary of Survey Responses From State and Local Highway Agencies." National Academies of Sciences, Engineering, and Medicine. 2004. Safety of U-Turns at Unsignalized Median Openings. Washington, DC: The National Academies Press. doi: 10.17226/13768.
×
Page 102
Page 103
Suggested Citation:"Appendix B - Summary of Survey Responses From State and Local Highway Agencies." National Academies of Sciences, Engineering, and Medicine. 2004. Safety of U-Turns at Unsignalized Median Openings. Washington, DC: The National Academies Press. doi: 10.17226/13768.
×
Page 103
Page 104
Suggested Citation:"Appendix B - Summary of Survey Responses From State and Local Highway Agencies." National Academies of Sciences, Engineering, and Medicine. 2004. Safety of U-Turns at Unsignalized Median Openings. Washington, DC: The National Academies Press. doi: 10.17226/13768.
×
Page 104
Page 105
Suggested Citation:"Appendix B - Summary of Survey Responses From State and Local Highway Agencies." National Academies of Sciences, Engineering, and Medicine. 2004. Safety of U-Turns at Unsignalized Median Openings. Washington, DC: The National Academies Press. doi: 10.17226/13768.
×
Page 105

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

B-1 APPENDIX B SUMMARY OF SURVEY RESPONSES FROM STATE AND LOCAL HIGHWAY AGENCIES This appendix presents a summary of the responses to the survey questionnaire sent to state and local highway agencies concerning median openings at unsignalized intersections. The questionnaire addresses highway agency policies con- cerning location and design of median openings, treatment of U-turns at median openings, traffic operational and safety problems at median openings, and effectiveness of various mitigation measures. Appendix A presents the questionnaire that was used to conduct the survey. SURVEY RECIPIENTS The mailing list for the survey included: • 50 state highway agencies and • 109 local highway agencies (94 cities and 15 counties). Thus, a total of 159 survey questionnaires were mailed. The questionnaires for state highway agencies were gener- ally sent to the state traffic engineer. The names and addresses of the state traffic engineers were determined from the mem- bership roster of the AASHTO directory. Most of the local highway agency engineers on the mailing list for the questionnaires were obtained from the AASHTO directory. The local agencies include approximately two major cities from each state and 15 selected urban or suburban coun- ties. Rural counties were not surveyed because they are unlikely to operate many divided highways. RESPONSE RATE Table B-1 summarizes the responses to the median open- ing survey. A total of 65 responses were received out of the 159 questionnaires that were mailed. The responses received included 35 state agencies, 23 cities, and 7 counties. The over- all response rate was 41 percent, including a response rate of 70 percent for state highway agencies and 28 percent for local highway agencies. Table B-2 presents a list of the state and local highway agencies that responded to this survey. SUMMARY OF SURVEY RESPONSES The highway agency responses to each question in the sur- vey are summarized below. Where appropriate, the responses are tabulated. Highway agencies responded to survey ques- tions in a mixture of metric and U.S. customary units. In this appendix, the units of measurement used in presenting each response are those actually used by the respondents. Question 1—Criteria Used to Determine Location of Median Opening In Question 1, highway agencies were asked about the cri- teria they use to determine the location of median openings. The general types of policies used by the responding agencies to determine the location of median openings are summarized in Table B-3. The types of policies used by the responding agencies include: AASHTO policy, state or local design pol- icy, state or local access management policy, general guide- lines (lists of factors considered as an informal policy), and engineering judgment. Because of multiple responses by some agencies, the totals add to more than 100 percent. The responses indicate that about half of the responding agencies have formal policies concerning median opening location and about half have guidelines or informal policies. Table B-4 presents a list of the factors considered by high- way agencies in determining the location of median open- ings. The factors were identified from the highway agency responses to the questionnaire and from the formal and infor- mal policies that the state and local agencies submitted with their responses. The factors shown in Table B-4 are pre- sented in decreasing order of the frequency with which they were mentioned. Factors mentioned by some highway agen- cies may, in fact, be considered by others; however, the table shows only those factors identified in the survey response and accompanying materials. The responses in Table B-4 add up to more than the number of agencies responding because many agencies provided multiple responses. The three most commonly cited factors considered in determining the location of median openings were: proxim- ity to other median openings, traffic volumes, and locations and functional classes of public road intersections. Other fre- quently mentioned factors included sight distance, operational efficiency, safety, area type, speed, availability of sufficient length to accommodate left-turn lanes, and median width. Question 2—Types of Median Openings Highway agencies were asked about the types of median openings that they use. All agencies stated that they use con- ventional (i.e., nondirectional) median openings on divided highways. Table B-5 presents the number and percentage of state and local agencies that use directional median openings,

classified by relative frequency of usage. Most of the agen- cies use directional median openings either frequently or occasionally. Ten agencies stated that they typically use con- ventional median openings but that they occasionally use directional median openings. Nine agencies stated that they do not use directional median openings. Question 3—Minimum Spacing Between Median Openings Table B-6 summarizes the number and percentage of state and local agencies that have formal policies concerning the minimum spacing between median openings. Approximately B-2 55 percent of the state agencies have formal policies, while only 45 percent of the local agencies have such policies. Of the 12 local agencies that have formal policies for minimum spacing between median openings, seven were cities and five were counties. Table B-7 summarizes the number and percentage of state and local areas that have policies on spacing between median openings that differ between rural and urban areas. The tabu- lation of local agencies in this table does not include cities, because cities do not typically include rural areas. Among the 22 states that have formal policies on spacings between median openings, 16 states have different policies for rural and urban areas, while six do not. Of the five county agencies that TABLE B-1 Response rate for the highway agency survey Agency type Number of questionnaires mailed Number of responses received Response rate (%) State agencies 50 35 70.0 Local agencies 109 30 27.6 Total 159 65 40.9 TABLE B-2 List of highway agencies that responded to survey State highway agencies Local highway agencies Alabama City of Mobile, AL Alaska Borough of Matanuska-Susitna, AK Arizona City of El Cajon, CA California City of San Diego, CA Connecticut City of Loveland, CO Florida City of Albany, GA Georgia City of Peoria, IL Idaho City of Ann Arbor, MI Illinois City of Kansas City, MO Iowa City of Springfield, MO Kansas City of Henderson, NV Louisiana City of Concord, NH Massachusetts City of Newark, NJ Michigan City of Bismarck, ND Mississippi City of Fargo, ND Missouri City of Columbus, OH Nebraska City of Norman, OK Nevada City of Charleston, SC New Hampshire City of Nashville, TN New Mexico City of Houston, TX New York City of St. George, UT North Carolina City of Lynchburg, VA North Dakota Maricopa County, AZ Ohio Pima County, AZ Oklahoma Riverside County, CA Oregon Broward County, FL Pennsylvania Osceola County, FL Rhode Island Monroe County, NY South Carolina Fairfax County, VA Texas Utah Virginia West Virginia Wisconsin Wyoming

B-3 Number (percentage) of agencies Policy used to determine location of median opening State agencies Local agencies Total AASHTO policy 3 (9.7) 3 (12.0) 6 (10.7) State or local design policy 4 (12.9) 9 (36.0) 13 (23.2) State or local access management policy 6 (19.3) 4 (16.0) 10 (17.9) General guidelines, list of factors considered, or informal policy 17 (54.8) 13 (52.0) 30 (53.6) Engineering judgment 6 (19.3) 4 (16.0) 10 (17.9) Total number of agencies responding 31 25 56 Factors considered State agencies Local agencies Total Proximity to other median openings 15 11 26 Traffic volumes (particularly minor-road volumes) 12 13 25 Locations and functional classes of public road intersections 12 12 24 Sight distance 11 1 12 Operational efficiency 6 3 9 Safety 4 4 8 Area type (rural/suburban/urban) 5 2 7 Speed 3 4 7 Availability of sufficient length for left-turn lane 4 2 6 Median width 5 0 5 Truck volumes 2 1 3 Practicality of frontage roads 3 0 3 Grade within the median 2 1 3 Proximity to driveways 1 1 2 Emergency vehicle access needs 1 1 2 Parcel size/land use 0 2 2 Willingness of developer to pay cost of median opening 1 1 2 Location of current or future signalized intersections 2 0 2 Type of facility 1 0 1 Older drivers 1 0 1 Natural barriers 1 0 1 Roadway environment 1 0 1 Number (percentage) of agencies that use directional median openings Agency type Frequently Occasionally Not used Total State agencies 14 (51.9) 7 (25.9) 6 (22.2) 27 Local agencies 20 (77.0) 3 (11.5) 3 (11.5) 26 Total 34 (64.2) 10 (18.9) 9 (16.9) 53 TABLE B-3 General policy used to determine where to allow median openings TABLE B-4 Factors considered in determining the location of median openings TABLE B-5 Highway agency use of directional median openings

have policies on spacing between median openings, only one has a policy that distinguishes between rural and urban areas. Table B-8 presents median opening spacing policies of state highway agencies that had numerical spacing policies that could be easily summarized. Some agencies had policies that were based on more variable criteria such as left-turn queue lengths, sight distance, and traffic volumes, which are harder to summarize and are not included in Table B-8. Com- parable data for local agencies are presented in Table B-9. In response to this question, some agencies presented policies on minimum driveway or access-point spacing. These poli- cies are not included in the tables because there is not neces- sarily a median opening at every driveway or access point. It can be seen in Table B-8 that the states that have different spacing policies for rural and urban areas typically require higher median-opening spacings in rural areas than in urban areas. The values reported for minimum median opening spac- ing for rural areas varied from 150 to 800 m (500 to 2,640 ft), while the comparable minimum spacing for urban areas var- ied from 90 to 800 m (300 to 2,640 ft); however, the average minimum median opening spacing was 430 m (1,400 ft) in rural areas and 270 m (880 ft) in urban areas. Four state agen- cies stated desirable (rather than minimum) values for median opening spacing. Georgia also presented a maximum spac- ing policy for median openings (5,200 ft for rural areas and 1,320 ft in urban areas). Table B-9 presents the minimum spacings between median openings for the five cities and five counties that presented quantitative minimum median spacing values in response to the survey. The general trend of higher minimum median opening spacing at rural areas was still present, although the differences in median opening spacing between area types are not as large as those shown in Table B-8. All of the cities shown in the table had criteria for urban areas only. Only one county (Osceola County, FL), had policies on median open- B-4 ing spacing that differed between urban and rural areas. This county stated that they use the access management policy of their state DOT. Question 4—Location of Unsignalized Median Openings Question 4 asked highway agencies about their policies for location of unsignalized median openings. The answers received did not differ substantially from the responses pre- sented above in Tables B-3, B-4, B-8, and B-9. Table B-10 summarizes the number and percentage of agencies that indi- cated whether they had a formal policy concerning the loca- tion of unsignalized median openings. Two states attached their specific policies on sight distance for unsignalized median opening locations; these policies are summarized in Table B-11. New Mexico has minimum cri- teria for sight distance along the main road at intersections based on the posted speed and Virginia has minimum crite- ria based on the design speed. Question 5—Installation of Left-Turn Lanes at Unsignalized Median Openings Question 5 asks highway agencies about their criteria for installation of left-turn lanes at unsignalized median openings. A majority of the responding agencies require installation of left-turn lanes at unsignalized median openings in all or most cases. Table B-12 presents the number and percentage of agen- cies that require left-turn lanes. Sixteen of the 42 agencies that require left-turn lanes at unsignalized median openings stated that left-turn lanes are provided only where specific warrants are met; other agencies may have explicit warrants for left-turn lanes, as well. Most respondents indicated that their warrants were based on left-turn volumes. Two states presented volume Number (percentage) of agencies that have formal policies concerning minimum spacing between median openings Agency type Yes No Total State agencies 22 (64.7) 12 (35.3) 34 Local agencies 12 (42.9) 16 (57.1) 28 Total 34 (54.8) 28 (45.2) 62 Number (percentage) of agencies that have different policies concerning minimum spacing between median openings for rural and urban areas Agency type Yes No Total State agencies 16 (72.7) 6 (27.3) 22 Local agenciesa 1 (20.0) 4 (80.0) 5 Total 17 (63.0) 10 (37.0) 27 a County agencies only. TABLE B-6 Number of agencies that have a policy concerning minimum spacing between median openings TABLE B-7 Number of agencies that have different policies on median opening spacing for rural and urban areas

warrants for left-turn lanes at unsignalized median openings based on research by Harmelink (67). Question 6—Use of Indirect Left-Turn Treatments Question 6 asked highway agencies about their use of indi- rect left-turn treatments. Only two state agencies responded B-5 that they have a formal policy on the conditions under which direct left-turn access to intersections or driveways is replaced by indirect left-turn treatment. The research team is aware of one other state highway agency which did not respond to the survey, which clearly would have answered “Yes” to Ques- tion 6 had they responded. Table B-13 presents a summary of the state and local agency responses concerning use of indirect left-turn treatments. Minimum spacing (ft) State Rural Urban Comments Alabama 600 300 Arizona 1,320 660 For businesses generating high traffic volumes the minimum spacing is 330 ft California 1,640 1,640 Unsure of possible differences between rural and urban criteria Florida 1,320 2,640 330-660 660-1,320 Directional Conventional Georgia 1,320 660 Maximum spacing 5,200 ft in rural areas and 1,320 ft in urban areas Iowa 1,000 660 Idaho 1,312 660 Illinois 2,625 (minimum) 5,250 (desirable) 1,312 Longer minimum spacing used if needed to accommodate left turn lanes Louisiana 1,500 500 Maine – 1,312-1,640 (minor arterial) 1,640-1,968 (major arterial) Criteria apply to signalized median openings only Michigan 1,320 660 Desirable spacing Mississippi 1,760 880 North Carolina 1,500 700 (< 45 mph) 1,000 (45-55 mph) Urban spacing criteria vary with operating speed Nebraska 1,000 (minimum) 2,000 (desirable) 600 New Mexico 600 300 Nevada 660 – In urban areas, have criteria for access spacing rather than median opening spacing Ohio – – Have spacing criteria for driveways but not for median openings Oklahoma 2,640 (minimum) 5,280 (desirable) 1,320 Longer minimum spacing used if needed to accommodate left turn lanes Pennsylvania 1,500 1,500 South Carolina 1,000 500 Texas 1,320 – 2,640 1,320 – 2,640 Virginia 700-1,000 (35-45 mph) 500-650 (50-70 mph) 700–1,000 (35-45 mph) 500–650 (50-70 mph) Urban spacing criteria vary with design speed Range 500 – 2,640 300 – 2,640 Average 1,400 880 TABLE B-8 State policies on minimum spacing between median openings

B-6 Minimum spacing (ft) County Rural Urban Comments San Diego, CA – 600 Springfield, MO – 500 Fargo, ND – 600 (arterials) 300 (collectors) Concord, NH – 500 (commercial) 1,000 (suburban) For arterials and collectors Henderson, NV – 660 Maricopa County, AZ 660 660 For arterials and collectors Pima County, AZ 1,320 1,320 Riverside County, CA 330-1,320 330-1,320 Based on intersection spacing Osceola County, FL 1,320 2,640 330-660 660-1,320 Directional Conventional Broward County, FL 660 660 Range 660 – 2,640 330 – 1,320 Average 800 725 Number (percentage) of agencies that have formal policies concerning location of unsignalized median openings Agency type Yes No Total State agencies 15 (45.5) 18 (54.5) 33 Local agencies 9 (33.3) 18 (66.7) 27 Total 24 (40.0) 36 (60.0) 60 Speed (mph) State agency 30 35 40 45 50 55 60 65 70 New Mexico (based on posted speed) 200 250 325 400 475 550 650 725 – Virginia (based on design speed) – 400 475 525 600 650 700 – 825 Number (percentage) of agencies that require left-turn lanes at unsignalized median openings Agency type Yesa No Total State agencies 24 (75.0) 8 (25.0) 32 Local agencies 18 (64.3) 10 (35.7) 28 Total 42 (70.0) 18 (30.0) 60 a In many cases, left-turn lanes are required only if specific volume warrants are met. Number (percentage) of agencies that have formal policies on the use of indirect left-turn treatments Agency type Yes No Total State agencies 2 (6.1) 31 (93.9) 33 Local agencies 0 (0.0) 28 (100.0) 28 Total 2 (3.3) 59 (96.70) 61 TABLE B-9 Local agency policies on minimum median opening spacing TABLE B-10 Formal policies on location of unsignalized median openings TABLE B-11 Minimum sight distance (ft) along the major road for median openings TABLE B-12 Number of agencies that require left-turn lanes at unsignalized median openings TABLE B-13 Number of agencies with formal policies on the use of indirect left-turn treatments as an alternative to direct left-turn access

Question 7—Geometric Design Criteria for Median Openings Question 7 asked respondents whether they had geometric design criteria for median openings and if their policy differed from the AASHTO Green Book. Fifteen highway agencies (13 state agencies and two local agencies) provided copies of their geometric design policies in response to Question 7. The types of policies that the responding agencies indi- cated they used for geometric design of median openings were: AASHTO policy; state or local geometric design poli- cies; state or local access management policy; general guide- lines (list of factors considered as informal policies); and engineering judgment. Table B-14 summarizes the number of state and local agencies that use each of these policy types. Because of multiple responses by some agencies, the totals add to more than 100 percent. Most of the state and local agencies (approximately 70 per- cent) use AASHTO policies for geometric design of median openings; in many cases, these are supplemented by general guidelines, list of factors considered, or informal policies. Question 8—Raised Medians vs. Continuous Two-Way Left-Turn Lanes Question 8 asked respondents whether they had a formal policy on the use of raised medians versus continuous two- way left-turn lanes (TWLTLs). Table B-15 summarizes the number and percentage of state and local agencies that have such a policy. Most of the responding agencies (81 percent) do not have such a policy. Eleven of the 58 responding agencies provided copies of their policy on the use of raised medians versus continuous TWLTLs. The following sections on location, speed, lane B-7 width, and intersections summarize key elements of the highway agency policies that those agencies noted in their responses. Location • A TWLTL may be considered in developed areas with frequent commercial roadside access and with no more than two through lanes in each direction. • Any TWLTL must be clearly marked and adequately delineated (MUTCD). • A TWLTL may be used where average daily through traffic volumes are 10,000 to 20,000 veh/day (4 lanes) or 5,000 to 12,000 veh/day (2 lanes), and left-turn vol- umes are at least 70 midblock turns per 300 m during peak hour. High left-turning volumes combined with high ADT could possibly lead to operational and safety problems. Providing a raised median, with left turn and/or U-turn lanes should also be considered. • In areas where there are numerous access points along an existing roadway, continuous TWLTLs may increase mobility and reduce conflicts. This design may be con- sidered in suburban areas where there are numerous existing access points and where other solutions to con- trol access cannot be implemented. • Flush/traversable medians may be used in both the urban and suburban areas in conjunction with curb and gutter along the outside edges of the traveled way. For most applications, the flush TWLTL should be used. How- ever, in larger metropolitan areas, a traversable TWLTL may be used. TABLE B-14 Type of policy used for geometric design of median openings TABLE B-15 Policy on the use of raised medians versus continuous two-way left-turn lanes Policy used for geometric design of median openings State agencies Local agencies Total AASHTO policy 19 (67.9) 16 (76.2) 35 (71.4) State or local design policy 3 (10.7) 3 (14.3) 6 (12.2) State or local access management policy 5 (17.9) 1 (4.8) 6 (12.2) General guidelines, list of factors considered or informal policy 13 (46.4) 6 (28.6) 19 (38.8) Engineering judgment 1 (3.6) 0 (0.0) 1 (2.0) Total number of agencies responding 28 21 49 Number (percentage) of agencies that have formal policies on the use of raised medians vs. continuous two-way left-turn lanes Agency type Yes No Total State agencies 8 (26.7) 22 (73.3) 30 Local agencies 3 (10.7) 25 (89.3) 28 Total 11 (19.0) 47 (81.0) 58

• TWLTLs shall only be used with roadways having a maximum of two through lanes in each direction of travel (i.e., seven-lane TWLTLs are not used). • Continuous TWLTLs are primarily used on urban highways. • Continuous TWLTLs are primarily used on minor arterials. • Major street plan calls for continuous TWLTLs on all new urban arterials. Speed • A TWLTL is limited to arterials with operating speeds of 70 km/hr or less. • Continuous TWLTLs may be considered on urban, two- lane state highways with a posted speed of 45 mph or less. Where the posted speed is greater than 45 mph, place- ment of a nontraversable median should be considered. • Continuous TWLTLs should be considered on low-speed arterial highways (25 to 45 mph) with no heavy concen- trations of left-turn traffic. They also may be used where an arterial or major route must pass through a developed area having numerous street and driveway intersections and where it is impractical to limit left turns. • In commercial and industrial areas where property val- ues are high and rights-of-way for wide medians are dif- ficult to acquire, a paved flush traversable median 10- to 16-ft wide is the optimum design. • All arterials with design speeds or posted speeds ≥ 45 mph, base year traffic volumes ≤ 18,000 veh/day, and design year traffic volumes ≤ 24,000 veh/day will require a five-lane section (flush median). • All arterials with design speeds or posted speeds ≤ 45 mph and base year traffic volume ≤ 18,000 veh/day and design year traffic volume ≥ 24,000 veh/day will require a five-lane section (flush median). The project will be designed to incorporate a future 20-ft raised median. Right-of-way will be purchased for footprint determined by the 20-ft median typical section. Moni- toring of accidents and traffic volumes on a five-year cycle by the Safety Engineer in the Office of Traffic Operations will determine the need and implementation of a raised median section. • All urban arterials with base year traffic volumes ≥ 18,000 veh/day, design year traffic volumes ≥ 24,000 veh/day, and design speed ≤ 45 mph will have a 20-ft raised median. • All arterials with posted speeds ≥ 55 mph or design speeds ≥ 50 mph will require the design of a 44-ft depressed median or a positive barrier system. Lane Width • The preferred lane width is 4.5 m with a minimum lane width of 3.75 m. B-8 • The usual design widths are 3.3 m, 3.6 m, or 4 m. There is some evidence that a wide TWLTL encourages driv- ers to place their vehicles in an angular rather than par- allel turning position and thereby causes other vehicles to encroach on adjacent through lanes. Therefore, max- imum widths for flush TWLTL medians should be 4 m. • The minimum desirable width shall be 12 ft and the maximum 16 ft. • The minimum width for a TWLTL shall be 3.6 m. The preferred width is 4.2 m. Wider TWLTLs are occasion- ally provided to conform with local agency standards. However, TWLTLs wider than 4.2 m are not recom- mended, and in no case should the width of a TWLTL exceed 4.8 m. Additional width may encourage drivers in opposite directions to use the TWLTL simultaneously. Intersections • At minor intersections, the TWLTL should be extended up to the intersection. At major or signalized intersec- tions, the TWLTL should be terminated in advance of the intersection. • Raised medians will be constructed on multilane facili- ties at intersections that include one of the following: – High turning volumes relating to 18,000 veh/day (base year) and 24,000 veh/day (design year) – Accident rate greater than the state average for its classification. Excessive queue lengths (as determined by District Traffic Engineer) in conjunction with exces- sive number of driveways. Question 9—Consideration of U-Turn Maneuvers in Design and Location of Median Openings Question 9 asked respondents whether their agency’s pol- icy for designing and locating median openings makes spe- cific reference to U-turn maneuvers. Table B-16 presents the number and percentage of the state and local agencies that do consider U-turn maneuvers explicitly in their criteria. The responses indicate that only 16 percent of highway agencies have a formal policy on median opening design and location that considers U-turn maneuvers, while 84 percent of high- way agencies do not have such a policy. Six of the nine agencies that consider U-turn maneuvers in median opening design and location attached copies of their policy. Most of these agencies rely primarily on AASHTO geometric design policies or some variation of AASHTO policy in their own guidelines. One state agency adds 12 ft to the AASHTO guidance on median width to better accom- modate U-turn maneuvers, while another adds between 11 and 17 ft to the median width depending on the design vehi- cle. The factors mentioned in the policies for U-turn maneu- vers at unsignalized median openings include:

• Median width (based on design vehicles and potential for encroachment) (six agencies) • Traffic conditions including ADTs, truck volumes, and peak-hour turning movement counts (four agencies) • Sight distance (two agencies) • Ability to begin and end U-turn maneuvers on the inner lane next to the median (two agencies) • Accident frequency, particularly angle and rear-end col- lisions involving left- or U-turning vehicles (one agency) • Specific threshold accident history criteria, such as five or more left-turn or U-turn-related accidents per year, similar to MUTCD requirements (one agency) • Location of the median openings with respect to signal- ized intersections (one agency) • Presence of exclusive left-turn lanes (one agency) • Availability of alternate locations for left- and U-turn maneuvers (one agency) Question 10—Prohibition of U-Turn Maneuvers Question 10 asked highway agencies whether U-turn maneuvers were permitted or not permitted at specific types of median openings. Table B-17 summarizes the responses to this B-9 question for rural and urban areas and for unsignalized and sig- nalized median openings. Approximately 80 percent of the agencies that responded permit U-turns at all types of median openings. It should be noted that nine agencies (five states and four local agencies) generally prohibit U-turn maneuvers at unsignalized median openings. Question 11—Criteria for U-Turn Prohibitions at Median Openings Question 11 asked highway agencies whether they have for- mal policies on when to prohibit U-turn maneuvers at specific median openings. Most of the responding agencies (91 percent of states and 92 percent of local agencies) do have formal poli- cies concerning when to prohibit U-turns at median openings. Table B-18 summarizes the highway agency responses to this question. The agencies with formal policies prohibit U-turns in the following situations: • At all signalized intersections that have a right-turn over- lap phase from a side street approach on the left during the protected left-turn phase on the mainline roadway (one agency) TABLE B-16 Number of highway agencies with policies that consider U-turn maneuvers in design and location of median openings Number (percentage) of agencies that make specific reference to U-turn maneuvers in policies for design and location of median openings Agency type Yes No Total State agencies 7 (22.6) 24 (77.4) 31 Local agencies 2 (7.7) 24 (92.3) 26 Total 9 (15.8) 48 (84.2) 57 Number (percentage) of agencies that permit U-turns at specific types of median openings Agency type U-turns permitted U-turns not permitted Total Median Openings on Rural Highways State agencies 26 (83.9) 5 (16.1) 31 Local agenciesa 4 (100.0) 0 (0.0) 4 Total 30 (85.7) 5 (14.3) 35 Median Openings on Urban/Suburban Arterials State agencies 26 (83.9) 5 (16.1) 31 Local agencies 22 (84.6) 4 (15.4) 26 Total 48 (84.2) 9 (15.8) 57 Unsignalized Median Openings State agencies 26 (83.9) 5 (16.1) 31 Local agencies 22 (84.6) 4 (15.4) 26 Total 48 (84.2) 9 (15.8) 57 Signalized Median Openings State agencies 25 (80.6) 6 (19.4) 31 Local agencies 20 (76.9) 6 (23.1) 26 Total 45 (78.9) 12 (21.1) 57 a Includes county agencies only. TABLE B-17 Number of highway agencies that permit U-turns at specific types of median openings

• At any curve or on the approach to or near the crest of a grade where a U-turning vehicle cannot be seen by the driver of any other vehicle approaching from any direc- tion within 500 ft. In addition, any left turn or U-turn at an intersection that does not meet the minimum sight distance criteria standards for U-turns as established by AASHTO (one agency) • At intersections with a receiving pavement width of 24 ft or less and at which the average vehicle cannot exe- cute a U-turn maneuver in a single continuous move- ment (one agency) • At any location for which a review of accident history finds that a U-turn restriction should be implemented, possibly only for certain times of the day (one agency) • Geometric design criteria (not further specified) (one agency) • At signalized intersections (one agency) • If less than 37 ft of width is available from the inside of the left-turn curb to the curb of the opposing lanes (one agency) Two agencies stated that U-turns are prohibited at all median openings unless they are signed to permit U-turns. Some agencies that did not have formal policies on where to permit or prohibit U-turns have informal guidelines that are presented below: • U-turns are permitted only at locations having sufficient roadway width for maneuver (four agencies). • U-turns are prohibited based on accident rate or safety problems (three agencies). • U-turns are prohibited at signalized intersections where right-turn overlaps are allowed (two agencies). • U-turns are prohibited where they would create a sub- stantial number of conflicts (two agencies). • U-turns are prohibited in some school zones (one agency). B-10 • U-turns are prohibited to relieve congestion at median openings (one agency). • U-turns are permitted at unsignalized median openings where a specific need is identified (one agency). U-turns are prohibited where a need is identified through engineering judgment (one agency) Question 12—Median and Roadway Widths Required to Provide for U-turns at Unsignalized Median Openings Question 12 asked highway agencies about the median width required by their agencies to provide for U-turns at unsignalized median openings. Fifteen state and five local agencies (or 53 percent of the agencies responding) stated that they follow the AASHTO Green Book to determine the median and roadway widths required to provide for U-turns at unsignalized median openings. Specifically, these agencies use the median width policy shown in Green Book Exhibit 9-92. Five state and six local agencies (or 29 percent of the agencies responding) stated that they have no policy or use engineering judgment. Two state and five local agencies stated that they have specific policies that differ from AASHTO Green Book. These policies are summarized below: • One state uses minimum median widths that are from 11 ft and 17 ft wider than those presented in the Green Book. Table B-19 presents the values used by this state agency. • One state adds 12 ft to AASHTO median widths shown in the Green Book. • One city permits U-turns on roads with 100-ft rights-of- way. This allows three travel lanes or 36 ft of traveled way width to receive traffic. • One city establishes minimum median widths needs in the range of 10 to 20 ft based on the type of roadway. Number (percentage) of agencies that have formal policy concerning when to prohibit U-turns at median openings Agency type Yes No Total State agencies 3 (9.4) 29 (90.6) 32 Local agencies 2 (7.7) 24 (92.3) 26 Total 5 (8.8) 53 (91.2) 58 TABLE B-18 Number of agencies that have formal policies on when to prohibit U-turns at median openings Type and length of design vehicle Type of maneuver P (19 ft) SU (30 ft) Bus (40 ft) WB-50 (55 ft) WB-60 (70 ft) Left lane to inner lane 44 76 80 82 82 Left lane to 2nd lane 32 64 68 70 70 Left lane to 3rd lane 22 54 58 60 60 TABLE B-19 Minimum median widths (ft) for U-turns used by one state highway agency

• One city allows U-turns on roads with a minimum width of six lanes that include turn lanes. • One city permits U-turns on arterials with a minimum width of 42 ft, which includes a 4-ft separator, 33 ft of travel lane width, and 5 ft of bike lane width. • One county stated that they permit U-turns with a median width of 14 ft and roadway width for one direction of travel of 26 ft. • One county stated that they permit U-turns with a median width between 20 and 24 ft and directional roadway width between 30 and 36 ft for a four-lane divided highway. Question 13—Increase in U-Turning Vehicle Volumes When a Nontraversable Median is Installed Question 13 asked highway agencies whether they had experienced an increase in the volume of U-turning vehicles when a nontraversable median was installed. Most agencies (79 percent) responded that they had experienced an increase. Table B-20 summarizes the responses to this question. Question 14—Provision for School Buses, Other Buses, and/or Large Trucks Question 14 asked highway agencies whether their criteria for design of median openings included provisions for school B-11 buses, other buses, and/or large trucks. Table B-21 summa- rizes the responses to Question 14. Approximately half of the responding state agencies indicated that they made provisions for U-turns by large vehicles at unsignalized median open- ings. Only one local agency stated that they had made such a provision. Question 15—Traffic Volume Threshold to Signalizing a Median Opening Question 15 asked highway agencies whether they had any established traffic volume thresholds or other established cri- teria for signalizing median openings that differed from the general MUTCD warrants for signalizing intersections. None of the responding agencies presented any criteria for signaliz- ing median openings that differ from MUTCD signal warrants. Question 16—Safety or Operational Problems at Unsignalized Median Openings Question 16 asked highway agencies whether they had experienced safety or traffic operational problems at unsig- nalized median openings. Table B-22 shows the number and percentage of highway agencies that indicated that they had experienced such problems at unsignalized median openings. Twenty-nine out of the 49 agencies that responded to this question (59 percent) indicated that they have encountered Number (percentage) of agencies that experienced an increase in U-turn volumes when a nontraversable median is installed Agency type Yes No Total State agencies 11 (73.3) 4 (26.7) 15 Local agencies 15 (83.3) 3 (16.7) 18 Total 26 (78.8) 7 (21.2) 33 Number (percentage) of agencies that make provision for school buses, other buses, or large trucks in design of median openings Agency type Yes No Total State agencies 10 (52.6) 9 (47.4) 19 Local agencies 1 (5.9) 16 (94.1) 17 Total 11 (30.6) 25 (69.4) 36 Number (percentage) of agencies that have encountered safety or operational problems at unsignalized median openings Agency type Yes No Total State agencies 12 (48.0) 13 (52.0) 25 Local agencies 17 (70.8) 7 (29.2) 24 Total 29 (59.2) 20 (40.8) 49 TABLE B-20 Number of agencies that have experienced an increase in U-turn volumes when a nontraversable median is installed TABLE B-21 Number of agencies that make provisions for school buses, other buses, and large trucks in design of unsignalized median openings TABLE B-22 Number of agencies that have encountered safety or operational problems at unsignalized median openings

safety or operational problems at unsignalized median open- ings. Table B-23 presents factors that the responding agen- cies indicated were related to the safety or operational prob- lems they encountered. Based on Table B-23, the five most cited factors that are related to safety or operational problems at unsignalized median openings in decreasing order are: • Operational considerations (e.g., heavy U-turns or through volumes, trucks, etc) • Median too narrow • Driveway nearby • Poor roadway geometry • Roadway too narrow All factors presented in Table B-23 were cited by eight or more agencies as contributing to safety or operational prob- lems at unsignalized median openings. Some additional fac- tors cited by the agencies include: • High speed on approaches to median opening (one agency) • Excessive number of conflict points for crossing traffic (one agency) B-12 • High number of accidents at median opening when road- way was converted from a two-lane to a four-lane facil- ity (one agency) Question 17—Mitigation of Safety and Operational Problems at Unsignalized Median Openings Question 17 asked highway agencies about mitigation measures they had used in response to safety and operational problems at unsignalized median openings. Table B-24 pre- sents the number and percentage of agencies that have con- structed improvement projects intended to mitigate safety and operational problems at unsignalized median openings. Thirty-seven percent of the agencies stated that they had con- structed such improvements. Some of the mitigation measures for safety and opera- tional problems cited are presented below: • Removal of closely spaced median openings by replac- ing raised medians with TWLTLs (four agencies) • Replacement of conventional crossovers with directional crossovers (two agencies) Number of agencies State agencies Local agencies Total Factors related to safety or operational problems Yes No Yes No Yes No Operational considerations (congestion, trucks) 10 0 10 7 20 7 Median too narrow 10 1 6 10 16 11 Driveway nearby 6 3 10 8 16 11 Poor roadway geometry 8 1 7 9 15 10 Roadway too narrow 8 3 6 11 14 14 Median opening within the functional area of an intersection 5 4 7 8 12 12 Insufficient sight distance 6 3 5 10 11 13 Frequency/density of median openings 4 6 6 9 10 15 Median opening across from right-turn lane 3 7 1 14 4 21 Median opening too long 5 5 4 11 9 16 Median opening within left-turn lane 4 5 4 12 8 17 Inconsistent application 4 5 5 9 9 14 Median too wide 4 6 4 11 8 17 TABLE B-23 Factors identified by highway agencies as related to the safety or operational problems they encountered at unsignalized median openings Number (percentage) of agencies that have constructed improvement projects to mitigate safety and operational problems at unsignalized median openings Agency type Yes No Total State agencies 13 (44.8) 16 (55.2) 29 Local agencies 8 (29.6) 19 (70.4) 27 Total 21 (37.5) 35 (62.5) 56 TABLE B-24 Number of agencies that have constructed improvement projects to mitigate safety or operational problems at unsignalized median openings

• Installation of left-turn storage lanes (two agencies) • Installation of left-turn lanes with positive offset (two agencies) • Signalize intersection (two agencies) • Close median openings to allow left turns to align prop- erly (one agency) • Reconfigure median openings by channelizing or adding left-turn lanes to prevent congestion or confusion in the median opening (one agency) • Installation of directional median openings to permit left turns from the major-road left-turn lane, but prohibit left turns and through movements from the minor road (one agency) • Provide a median opening at what formerly was a right- in/right-out driveway (one agency) • Eliminate conventional median openings and replace with jughandle U-turns (one agency) • Installation of “No U-turn” signs (one agency) • Installation of raised/extended median to prevent U-turns (one agency) Table B-25 presents the number and percentage of agen- cies that have conducted formal before-after evaluations of improvement projects that were constructed to mitigate the safety and operational problems at unsignalized median openings. Six agencies indicated that they have performed such evaluations. Question 18—Suitable Candidate Sites for Accident and Field Evaluations In Question 18, highway agencies were asked to identify types of median openings under their jurisdiction and that B-13 might be suitable candidates for accident and field evaluation later in this research. Table B-26 identifies the types of median openings that were identified by responding agencies as poten- tially available for evaluation. Question 19—Increase in U-Turn Volumes at Adjacent Median Openings Caused by the Installation of Raised Medians to Eliminate Direct Left-Turn Access to Intersections or Driveways In Question 19, highway agencies were asked whether they had experienced increases in U-turn volumes at median openings, as a result of projects in which a raised median that eliminated direct left-turn access to one or more intersections or driveways was installed. Table B-27 shows that more than half of the responding agencies indicated that they had imple- mented such projects recently (during the last 5 to 7 years) in their jurisdiction. Ten state and 15 local agencies estimated the approximate number of such projects; these estimates are presented in Table B-28. Table B-29 presents the number and percentage of state and local agencies that encountered safety or operational prob- lems related to the installation of raised medians. Only three agencies indicated that they had encountered such safety or operational problems. Only one agency stated the type of problem which was that a small number of drivers made ille- gal U-turns or mounted the median to cross it. The state and local agencies were asked if they have per- formed any formal before-after evaluation of projects in which a raised median was installed which eliminated direct left- turn access to intersection or driveways. Table B-30 summa- rizes the responses to this question. Only one state indicated Number (percentage) of agencies that have conducted evaluations of improvement projects intended to mitigate the safety and operational problems at unsignalized median openings Agency type Yes No Total State agencies 4 (14.3) 24 (85.7) 28 Local agencies 2 (7.4) 25 (92.6) 27 Total 6 (10.9) 49 (89.1) 55 Number of agencies State agencies Local agencies Total Types of median openings that might be suitable candidates for evaluation Yes No Yes No Yes No Urban 17 5 19 3 36 8 Rural 20 3 4 13 24 16 Wide median 14 7 9 11 23 18 Narrow median 18 3 11 8 29 11 Signalized 10 8 15 6 25 14 Unsignalized 18 3 18 4 36 7 Conventional (full movement) 18 3 17 4 35 7 Directional 12 8 13 6 25 14 TABLE B-25 Number of agencies that have performed formal before-after evaluations of improvement projects at unsignalized median openings TABLE B-26 Types of median openings that might be suitable candidates for accident and field evaluation

that they had performed such an evaluation. Table B-31 pre- sents the number of state and local agencies that indicated that they have projects that may potentially be suitable for evaluation as part of this research. A total of 13 agencies (four state and nine local agencies) responded that they had poten- tially suitable projects available. Question 20—Closing of Existing Unsignalized Median Opening Resulting in Increased U-Turn Volumes at Median Openings Elsewhere on the Same Roadway Question 20 asked highway agencies whether they had implemented projects in which existing unsignalized median B-14 openings were closed eliminating direct left-turn access to one or more intersections or driveways, and resulting in increased U-turn volumes at median openings elsewhere on the same roadway. The responses to this question are summarized in Table B-32. Thirty-seven percent of the agencies indicated that they had implemented such projects recently (during the last 5 to 7 years) in their jurisdiction. Eleven agencies esti- mated the approximate number of such projects; these esti- mates are summarized in Table B-33. Table B-34 shows the number of agencies that had expe- rienced safety or operational problems resulting from proj- ects in which an existing unsignalized median opening was closed. It can be seen in the Table B-34 that only one state answered that it had encountered such problems; this agency Agency type Yes No Total State agencies 14 (46.7) 16 (53.3) 30 Local agencies 16 (61.5) 10 (38.5) 26 Total 30 (53.6) 26 (46.4) 56 Number (percentage) of agencies that have recently implemented projects in which a raised median was installed to eliminate direct left-turn access to intersection or driveways and resulted in increased U-turn volumes at median openings elsewhere TABLE B-27 Number of agencies that experienced an increase in U-turn volumes at median openings when raised medians were installed which eliminated direct left-turn access to intersection or driveways Agency type Number of agencies Total number of projects Average number of projects per agency State agencies 9 107 12 Local agencies 15 32 2 Total 24 139 7 Number (percentage) of agencies that experienced safety or operational problems related to U-turn maneuvers in conjunction with projects in which a raised median was installed Agency type Yes No Total State agencies 0 (0.0) 19 (100.0) 19 Local agencies 3 (14.3) 18 (85.7) 21 Total 3 (7.5) 37 (92.5) 40 Number (percentage) of agencies that have performed formal before-after evaluations of projects in which a raised median was installed and direct left-turn access to intersection or driveways was eliminated Agency type Yes No Total State agencies 1 (3.4) 28 (96.6) 29 Local agencies 0 (0.0) 22 (100.0) 22 Total 1 (2.0) 50 (98.0) 51 TABLE B-28 Number of agencies and estimated number of projects that installed raised median and eliminated direct left-turn access to intersections and driveways resulting in an increase in U-turn volumes at adjacent median openings TABLE B-29 Number of agencies that experienced safety or operational problems related to the increased U-turn maneuvers resulting from installation of raised medians TABLE B-30 Number of agencies that have performed formal before-after evaluations of projects involving raised medians

did not specify the nature of the problem other than to say that it involved an increase in U-turns at other locations. The responding state and local agencies were also asked if they have performed any formal before-after evaluations of projects in which an unsignalized median opening was closed. Table B-35 summarizes the responses to this question. Three B-15 agencies indicated that they performed such evaluations. Table B-36 summarizes the number of state and local agen- cies that have projects involving closure of unsignalized median openings that may be suitable for evaluation as part of this research. Nine agencies (five state and four local agen- cies) indicated that they may have such projects. Number of agencies that have projects that are potentially suitable for evaluation as part of this research Agency type Yes No Total State agencies 4 (19.0) 17 (81.0) 21 Local agencies 9 (50.0) 9 (50.0) 18 Total 13 (33.3) 26 (66.7) 39 Number (percentage) of agencies that have recently implemented projects in which an existing unsignalized median opening was closed resulting in increased U-turn volumes at adjacent median openings Agency type Yes No Total State agencies 13 (56.7) 17 (43.3) 30 Local agencies 7 (29.2) 17 (70.8) 24 Total 20 (37.0) 34 (63.0) 54 Agency type Number of agencies that have such projects Total number of projects Average number of projects State agencies 7 78 11 Local agencies 4 12 3 Total 11 90 8 Number (percentage) of agencies that have safety or operational problems related to U-turn maneuvers in conjunction with projects in which unsignalized median openings were closed Agency type Yes No Total State agencies 1 (6.7) 14 (93.3) 15 Local agencies 0 (0.0) 16 (100.0) 16 Total 1 (3.2) 30 (96.8) 31 TABLE B-31 Number of agencies that indicated they have projects involving installation of raised medians that are potentially suitable for evaluation as part of this research TABLE B-32 Number of agencies that implemented projects that resulted in an increase in U-turn volumes due to closing of existing unsignalized median openings TABLE B-33 Number of agencies and estimated number of projects that closed existing unsignalized median openings TABLE B-34 Number of agencies that experienced safety or operational problems related to the closing of existing unsignalized median openings Number (percentage) of agencies that have performed formal before-after evaluations of projects involving closure of existing unsignalized median openings Agency type Yes No Total State agencies 2 (7.4) 25 (92.6) 27 Local agencies 1 (5.9) 16 (94.1) 17 Total 3 (6.8) 41 (93.2) 44 TABLE B-35 Number of agencies that have performed formal before-after evaluations of projects involving closure of an existing unsignalized median opening

B-16 Number (percentage) of agencies that may have suitable projects involving closure of existing unsignalized median openings for evaluation as part of this research Agency type Yes No Total State agencies 5 (23.8) 14 (76.2) 19 Local agencies 4 (30.8) 9 (69.2) 13 Total 9 (28.1) 23 (71.9) 32 TABLE B-36 Number of agencies that may have projects involving closure of existing unsignalized median openings that may be suitable for evaluation as part of this research

Next: Appendix C - Guidelines for the Use, Location, and Design of Unsignalized Median Openings »
Safety of U-Turns at Unsignalized Median Openings Get This Book
×
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

TRB’s National Cooperative Highway Research Program (NCHRP) Report 524: Safety of U-Turns at Unsignalized Median Openings includes recommended guidelines for locating and designing unsignalized median openings, and a methodology for comparing the relative safety performance of different designs.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!