Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 90
B-1 APPENDIX B SUMMARY OF SURVEY RESPONSES FROM STATE AND LOCAL HIGHWAY AGENCIES This appendix presents a summary of the responses to the appendix, the units of measurement used in presenting each survey questionnaire sent to state and local highway agencies response are those actually used by the respondents. concerning median openings at unsignalized intersections. The questionnaire addresses highway agency policies con- cerning location and design of median openings, treatment of Question 1--Criteria Used to Determine Location of Median Opening U-turns at median openings, traffic operational and safety problems at median openings, and effectiveness of various In Question 1, highway agencies were asked about the cri- mitigation measures. Appendix A presents the questionnaire teria they use to determine the location of median openings. that was used to conduct the survey. The general types of policies used by the responding agencies to determine the location of median openings are summarized SURVEY RECIPIENTS in Table B-3. The types of policies used by the responding agencies include: AASHTO policy, state or local design pol- The mailing list for the survey included: icy, state or local access management policy, general guide- lines (lists of factors considered as an informal policy), and · 50 state highway agencies and engineering judgment. Because of multiple responses by · 109 local highway agencies (94 cities and 15 counties). some agencies, the totals add to more than 100 percent. The responses indicate that about half of the responding agencies Thus, a total of 159 survey questionnaires were mailed. have formal policies concerning median opening location The questionnaires for state highway agencies were gener- and about half have guidelines or informal policies. ally sent to the state traffic engineer. The names and addresses Table B-4 presents a list of the factors considered by high- of the state traffic engineers were determined from the mem- way agencies in determining the location of median open- bership roster of the AASHTO directory. ings. The factors were identified from the highway agency Most of the local highway agency engineers on the mailing responses to the questionnaire and from the formal and infor- list for the questionnaires were obtained from the AASHTO mal policies that the state and local agencies submitted with directory. The local agencies include approximately two major their responses. The factors shown in Table B-4 are pre- cities from each state and 15 selected urban or suburban coun- sented in decreasing order of the frequency with which they ties. Rural counties were not surveyed because they are were mentioned. Factors mentioned by some highway agen- unlikely to operate many divided highways. 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 RESPONSE RATE to more than the number of agencies responding because many agencies provided multiple responses. Table B-1 summarizes the responses to the median open- The three most commonly cited factors considered in ing survey. A total of 65 responses were received out of the determining the location of median openings were: proxim- 159 questionnaires that were mailed. The responses received ity to other median openings, traffic volumes, and locations included 35 state agencies, 23 cities, and 7 counties. The over- and functional classes of public road intersections. Other fre- all response rate was 41 percent, including a response rate of quently mentioned factors included sight distance, operational 70 percent for state highway agencies and 28 percent for local efficiency, safety, area type, speed, availability of sufficient highway agencies. Table B-2 presents a list of the state and length to accommodate left-turn lanes, and median width. local highway agencies that responded to this survey. Question 2--Types of Median Openings SUMMARY OF SURVEY RESPONSES Highway agencies were asked about the types of median The highway agency responses to each question in the sur- openings that they use. All agencies stated that they use con- vey are summarized below. Where appropriate, the responses ventional (i.e., nondirectional) median openings on divided are tabulated. Highway agencies responded to survey ques- highways. Table B-5 presents the number and percentage of tions in a mixture of metric and U.S. customary units. In this state and local agencies that use directional median openings,
OCR for page 91
B-2 TABLE B-1 Response rate for the highway agency survey Number of Number of responses Response Agency type questionnaires mailed received rate (%) State agencies 50 35 70.0 Local agencies 109 30 27.6 Total 159 65 40.9 classified by relative frequency of usage. Most of the agen- 55 percent of the state agencies have formal policies, while cies use directional median openings either frequently or only 45 percent of the local agencies have such policies. Of occasionally. Ten agencies stated that they typically use con- the 12 local agencies that have formal policies for minimum ventional median openings but that they occasionally use spacing between median openings, seven were cities and five directional median openings. Nine agencies stated that they were counties. do not use directional median openings. 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- Question 3--Minimum Spacing Between Median Openings lation of local agencies in this table does not include cities, because cities do not typically include rural areas. Among Table B-6 summarizes the number and percentage of state the 22 states that have formal policies on spacings between and local agencies that have formal policies concerning the median openings, 16 states have different policies for rural and minimum spacing between median openings. Approximately urban areas, while six do not. Of the five county agencies that 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
OCR for page 92
B-3 TABLE B-3 General policy used to determine where to allow median openings Policy used to Number (percentage) of agencies determine location of median opening State agencies Local agencies Total AASHTO policy 3 (9.7) 3 (12.0) 6 (10.7) State or local 4 (12.9) 9 (36.0) 13 (23.2) design policy State or local 6 (19.3) 4 (16.0) 10 (17.9) access management policy General 17 (54.8) 13 (52.0) 30 (53.6) guidelines, list of factors considered, or informal policy Engineering 6 (19.3) 4 (16.0) 10 (17.9) judgment Total number of 31 25 56 agencies responding TABLE B-4 Factors considered in determining the location of median openings Factors considered State agencies Local agencies Total Proximity to other median openings 15 11 26 Traffic volumes (particularly minor-road 12 13 25 volumes) Locations and functional classes of public 12 12 24 road intersections 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 1 1 2 median opening Location of current or future signalized 2 0 2 intersections Type of facility 1 0 1 Older drivers 1 0 1 Natural barriers 1 0 1 Roadway environment 1 0 1 TABLE B-5 Highway agency use of directional median openings 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
OCR for page 93
B-4 TABLE B-6 Number of agencies that have a policy concerning minimum spacing between median openings 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 TABLE B-7 Number of agencies that have different policies on median opening spacing for rural and urban areas 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. have policies on spacing between median openings, only one ing spacing that differed between urban and rural areas. This has a policy that distinguishes between rural and urban areas. county stated that they use the access management policy of Table B-8 presents median opening spacing policies of their state DOT. state highway agencies that had numerical spacing policies that could be easily summarized. Some agencies had policies Question 4--Location of Unsignalized Median that were based on more variable criteria such as left-turn Openings queue lengths, sight distance, and traffic volumes, which are harder to summarize and are not included in Table B-8. Com- Question 4 asked highway agencies about their policies parable data for local agencies are presented in Table B-9. In for location of unsignalized median openings. The answers response to this question, some agencies presented policies received did not differ substantially from the responses pre- on minimum driveway or access-point spacing. These poli- sented above in Tables B-3, B-4, B-8, and B-9. Table B-10 cies are not included in the tables because there is not neces- summarizes the number and percentage of agencies that indi- sarily a median opening at every driveway or access point. cated whether they had a formal policy concerning the loca- It can be seen in Table B-8 that the states that have different tion of unsignalized median openings. spacing policies for rural and urban areas typically require Two states attached their specific policies on sight distance higher median-opening spacings in rural areas than in urban for unsignalized median opening locations; these policies are areas. The values reported for minimum median opening spac- summarized in Table B-11. New Mexico has minimum cri- ing for rural areas varied from 150 to 800 m (500 to 2,640 ft), teria for sight distance along the main road at intersections while the comparable minimum spacing for urban areas var- based on the posted speed and Virginia has minimum crite- ied from 90 to 800 m (300 to 2,640 ft); however, the average ria based on the design speed. minimum median opening spacing was 430 m (1,400 ft) in rural areas and 270 m (880 ft) in urban areas. Four state agen- Question 5--Installation of Left-Turn Lanes cies stated desirable (rather than minimum) values for median at Unsignalized Median Openings opening spacing. Georgia also presented a maximum spac- ing policy for median openings (5,200 ft for rural areas and Question 5 asks highway agencies about their criteria for 1,320 ft in urban areas). installation of left-turn lanes at unsignalized median openings. Table B-9 presents the minimum spacings between median A majority of the responding agencies require installation of openings for the five cities and five counties that presented left-turn lanes at unsignalized median openings in all or most quantitative minimum median spacing values in response to cases. Table B-12 presents the number and percentage of agen- the survey. The general trend of higher minimum median cies that require left-turn lanes. Sixteen of the 42 agencies that opening spacing at rural areas was still present, although the require left-turn lanes at unsignalized median openings stated differences in median opening spacing between area types that left-turn lanes are provided only where specific warrants are not as large as those shown in Table B-8. All of the cities are met; other agencies may have explicit warrants for left-turn shown in the table had criteria for urban areas only. Only one lanes, as well. Most respondents indicated that their warrants county (Osceola County, FL), had policies on median open- were based on left-turn volumes. Two states presented volume
OCR for page 94
B-5 TABLE B-8 State policies on minimum spacing between median openings 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 1,320 330-660 Directional 2,640 660-1,320 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) 1,312 Longer minimum spacing 5,250 (desirable) used if needed to accommodate left turn lanes Louisiana 1,500 500 Maine 1,312-1,640 (minor arterial) Criteria apply to 1,640-1,968 (major arterial) signalized median openings only Michigan 1,320 660 Desirable spacing Mississippi 1,760 880 North Carolina 1,500 700 (< 45 mph) Urban spacing criteria 1,000 (45-55 mph) vary with operating speed Nebraska 1,000 (minimum) 600 2,000 (desirable) 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) 1,320 Longer minimum spacing 5,280 (desirable) 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) 7001,000 (35-45 mph) Urban spacing criteria 500-650 (50-70 mph) 500650 (50-70 mph) vary with design speed Range 500 2,640 300 2,640 Average 1,400 880 warrants for left-turn lanes at unsignalized median openings that they have a formal policy on the conditions under which based on research by Harmelink (67). 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 Question 6--Use of Indirect Left-Turn Treatments survey, which clearly would have answered "Yes" to Ques- tion 6 had they responded. Table B-13 presents a summary Question 6 asked highway agencies about their use of indi- of the state and local agency responses concerning use of rect left-turn treatments. Only two state agencies responded indirect left-turn treatments.
OCR for page 95
B-6 TABLE B-9 Local agency policies on minimum median opening spacing Minimum spacing (ft) County Rural Urban Comments San Diego, CA 600 Springfield, MO 500 Fargo, ND 600 (arterials) 300 (collectors) Concord, NH 500 (commercial) For arterials and 1,000 (suburban) 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 1,320 330-660 Directional 2,640 660-1,320 Conventional Broward County, FL 660 660 Range 660 2,640 330 1,320 Average 800 725 TABLE B-10 Formal policies on location of unsignalized median openings 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 TABLE B-11 Minimum sight distance (ft) along the major road for median openings Speed (mph) State agency 30 35 40 45 50 55 60 65 70 New Mexico (based 200 250 325 400 475 550 650 725 on posted speed) Virginia (based on 400 475 525 600 650 700 825 design speed) TABLE B-12 Number of agencies that require left-turn lanes at unsignalized median openings 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. 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 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
OCR for page 96
B-7 Question 7--Geometric Design Criteria for width, and intersections summarize key elements of the Median Openings highway agency policies that those agencies noted in their responses. 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 Location 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 · A TWLTL may be considered in developed areas with were: AASHTO policy; state or local geometric design poli- frequent commercial roadside access and with no more cies; state or local access management policy; general guide- than two through lanes in each direction. lines (list of factors considered as informal policies); and · Any TWLTL must be clearly marked and adequately engineering judgment. Table B-14 summarizes the number delineated (MUTCD). of state and local agencies that use each of these policy types. · A TWLTL may be used where average daily through Because of multiple responses by some agencies, the totals traffic volumes are 10,000 to 20,000 veh/day (4 lanes) add to more than 100 percent. or 5,000 to 12,000 veh/day (2 lanes), and left-turn vol- Most of the state and local agencies (approximately 70 per- umes are at least 70 midblock turns per 300 m during cent) use AASHTO policies for geometric design of median peak hour. High left-turning volumes combined with openings; in many cases, these are supplemented by general high ADT could possibly lead to operational and safety guidelines, list of factors considered, or informal policies. 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 Question 8--Raised Medians vs. Continuous Two-Way Left-Turn Lanes an existing roadway, continuous TWLTLs may increase mobility and reduce conflicts. This design may be con- Question 8 asked respondents whether they had a formal sidered in suburban areas where there are numerous policy on the use of raised medians versus continuous two- existing access points and where other solutions to con- way left-turn lanes (TWLTLs). Table B-15 summarizes the trol access cannot be implemented. number and percentage of state and local agencies that have · Flush/traversable medians may be used in both the urban such a policy. Most of the responding agencies (81 percent) and suburban areas in conjunction with curb and gutter do not have such a policy. along the outside edges of the traveled way. For most Eleven of the 58 responding agencies provided copies of applications, the flush TWLTL should be used. How- their policy on the use of raised medians versus continuous ever, in larger metropolitan areas, a traversable TWLTL TWLTLs. The following sections on location, speed, lane may be used. TABLE B-14 Type of policy used for geometric design of median openings Policy used for geometric design of median Local openings State agencies 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 13 (46.4) 6 (28.6) 19 (38.8) or informal policy Engineering judgment 1 (3.6) 0 (0.0) 1 (2.0) Total number of agencies responding 28 21 49 TABLE B-15 Policy on the use of raised medians versus continuous two-way left-turn lanes 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
OCR for page 97
B-8 · TWLTLs shall only be used with roadways having a · The usual design widths are 3.3 m, 3.6 m, or 4 m. There maximum of two through lanes in each direction of is some evidence that a wide TWLTL encourages driv- travel (i.e., seven-lane TWLTLs are not used). ers to place their vehicles in an angular rather than par- · Continuous TWLTLs are primarily used on urban allel turning position and thereby causes other vehicles highways. to encroach on adjacent through lanes. Therefore, max- · Continuous TWLTLs are primarily used on minor imum widths for flush TWLTL medians should be 4 m. arterials. · The minimum desirable width shall be 12 ft and the · Major street plan calls for continuous TWLTLs on all maximum 16 ft. new urban arterials. · The minimum width for a TWLTL shall be 3.6 m. The preferred width is 4.2 m. Wider TWLTLs are occasion- Speed ally provided to conform with local agency standards. However, TWLTLs wider than 4.2 m are not recom- · A TWLTL is limited to arterials with operating speeds mended, and in no case should the width of a TWLTL of 70 km/hr or less. exceed 4.8 m. Additional width may encourage drivers in · Continuous TWLTLs may be considered on urban, two- opposite directions to use the TWLTL simultaneously. 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. Intersections · Continuous TWLTLs should be considered on low-speed · At minor intersections, the TWLTL should be extended arterial highways (25 to 45 mph) with no heavy concen- trations of left-turn traffic. They also may be used where up to the intersection. At major or signalized intersec- an arterial or major route must pass through a developed tions, the TWLTL should be terminated in advance of area having numerous street and driveway intersections the intersection. and where it is impractical to limit left turns. · Raised medians will be constructed on multilane facili- · In commercial and industrial areas where property val- ties at intersections that include one of the following: ues are high and rights-of-way for wide medians are dif- High turning volumes relating to 18,000 veh/day (base ficult to acquire, a paved flush traversable median 10- to year) and 24,000 veh/day (design year) 16-ft wide is the optimum design. Accident rate greater than the state average for its · All arterials with design speeds or posted speeds classification. Excessive queue lengths (as determined 45 mph, base year traffic volumes 18,000 veh/day, by District Traffic Engineer) in conjunction with exces- and design year traffic volumes 24,000 veh/day will sive number of driveways. 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 Question 9--Consideration of U-Turn Maneuvers in Design and Location of Median and design year traffic volume 24,000 veh/day will Openings require a five-lane section (flush median). The project will be designed to incorporate a future 20-ft raised Question 9 asked respondents whether their agency's pol- median. Right-of-way will be purchased for footprint icy for designing and locating median openings makes spe- determined by the 20-ft median typical section. Moni- cific reference to U-turn maneuvers. Table B-16 presents the toring of accidents and traffic volumes on a five-year number and percentage of the state and local agencies that do cycle by the Safety Engineer in the Office of Traffic consider U-turn maneuvers explicitly in their criteria. The Operations will determine the need and implementation responses indicate that only 16 percent of highway agencies of a raised median section. have a formal policy on median opening design and location · All urban arterials with base year traffic volumes that considers U-turn maneuvers, while 84 percent of high- 18,000 veh/day, design year traffic volumes 24,000 way agencies do not have such a policy. veh/day, and design speed 45 mph will have a 20-ft Six of the nine agencies that consider U-turn maneuvers in raised median. median opening design and location attached copies of their · All arterials with posted speeds 55 mph or design policy. Most of these agencies rely primarily on AASHTO speeds 50 mph will require the design of a 44-ft geometric design policies or some variation of AASHTO depressed median or a positive barrier system. policy in their own guidelines. One state agency adds 12 ft to the AASHTO guidance on median width to better accom- Lane Width modate U-turn maneuvers, while another adds between 11 and 17 ft to the median width depending on the design vehi- · The preferred lane width is 4.5 m with a minimum lane cle. The factors mentioned in the policies for U-turn maneu- width of 3.75 m. vers at unsignalized median openings include:
OCR for page 98
B-9 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 · Median width (based on design vehicles and potential question for rural and urban areas and for unsignalized and sig- for encroachment) (six agencies) nalized median openings. Approximately 80 percent of the · Traffic conditions including ADTs, truck volumes, and agencies that responded permit U-turns at all types of median peak-hour turning movement counts (four agencies) openings. It should be noted that nine agencies (five states and · Sight distance (two agencies) four local agencies) generally prohibit U-turn maneuvers at · Ability to begin and end U-turn maneuvers on the inner unsignalized median openings. lane next to the median (two agencies) · Accident frequency, particularly angle and rear-end col- Question 11--Criteria for U-Turn Prohibitions at lisions involving left- or U-turning vehicles (one agency) Median Openings · Specific threshold accident history criteria, such as five or more left-turn or U-turn-related accidents per year, Question 11 asked highway agencies whether they have for- similar to MUTCD requirements (one agency) mal policies on when to prohibit U-turn maneuvers at specific · Location of the median openings with respect to signal- median openings. Most of the responding agencies (91 percent ized intersections (one agency) of states and 92 percent of local agencies) do have formal poli- · Presence of exclusive left-turn lanes (one agency) cies concerning when to prohibit U-turns at median openings. · Availability of alternate locations for left- and U-turn Table B-18 summarizes the highway agency responses to this maneuvers (one agency) question. The agencies with formal policies prohibit U-turns in the following situations: Question 10--Prohibition of U-Turn Maneuvers · At all signalized intersections that have a right-turn over- Question 10 asked highway agencies whether U-turn lap phase from a side street approach on the left during maneuvers were permitted or not permitted at specific types of the protected left-turn phase on the mainline roadway median openings. Table B-17 summarizes the responses to this (one agency) TABLE B-17 Number of highway agencies that permit U-turns at specific types of median openings 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.
OCR for page 99
B-10 TABLE B-18 Number of agencies that have formal policies on when to prohibit U-turns at median openings 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 · At any curve or on the approach to or near the crest of a · U-turns are prohibited to relieve congestion at median grade where a U-turning vehicle cannot be seen by the openings (one agency). driver of any other vehicle approaching from any direc- · U-turns are permitted at unsignalized median openings tion within 500 ft. In addition, any left turn or U-turn at where a specific need is identified (one agency). an intersection that does not meet the minimum sight distance criteria standards for U-turns as established by U-turns are prohibited where a need is identified through AASHTO (one agency) engineering judgment (one agency) · At intersections with a receiving pavement width of 24 ft or less and at which the average vehicle cannot exe- Question 12--Median and Roadway Widths cute a U-turn maneuver in a single continuous move- Required to Provide for U-turns at Unsignalized ment (one agency) Median Openings · At any location for which a review of accident history finds that a U-turn restriction should be implemented, Question 12 asked highway agencies about the median possibly only for certain times of the day (one agency) width required by their agencies to provide for U-turns at · Geometric design criteria (not further specified) (one unsignalized median openings. Fifteen state and five local agency) agencies (or 53 percent of the agencies responding) stated · At signalized intersections (one agency) that they follow the AASHTO Green Book to determine the · If less than 37 ft of width is available from the inside of median and roadway widths required to provide for U-turns at unsignalized median openings. Specifically, these agencies the left-turn curb to the curb of the opposing lanes (one use the median width policy shown in Green Book Exhibit agency) 9-92. Five state and six local agencies (or 29 percent of the agencies responding) stated that they have no policy or use Two agencies stated that U-turns are prohibited at all median engineering judgment. Two state and five local agencies stated openings unless they are signed to permit U-turns. that they have specific policies that differ from AASHTO Some agencies that did not have formal policies on where Green Book. These policies are summarized below: to permit or prohibit U-turns have informal guidelines that are presented below: · One state uses minimum median widths that are from 11 ft and 17 ft wider than those presented in the Green · U-turns are permitted only at locations having sufficient Book. Table B-19 presents the values used by this state roadway width for maneuver (four agencies). agency. · U-turns are prohibited based on accident rate or safety · One state adds 12 ft to AASHTO median widths shown problems (three agencies). in the Green Book. · U-turns are prohibited at signalized intersections where · One city permits U-turns on roads with 100-ft rights-of- right-turn overlaps are allowed (two agencies). way. This allows three travel lanes or 36 ft of traveled · U-turns are prohibited where they would create a sub- way width to receive traffic. stantial number of conflicts (two agencies). · One city establishes minimum median widths needs in · U-turns are prohibited in some school zones (one agency). the range of 10 to 20 ft based on the type of roadway. TABLE B-19 Minimum median widths (ft) for U-turns used by one state highway agency 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
OCR for page 100
B-11 · One city allows U-turns on roads with a minimum width buses, other buses, and/or large trucks. Table B-21 summa- of six lanes that include turn lanes. rizes the responses to Question 14. Approximately half of the · One city permits U-turns on arterials with a minimum responding state agencies indicated that they made provisions width of 42 ft, which includes a 4-ft separator, 33 ft of for U-turns by large vehicles at unsignalized median open- travel lane width, and 5 ft of bike lane width. ings. Only one local agency stated that they had made such a · One county stated that they permit U-turns with a median provision. width of 14 ft and roadway width for one direction of travel of 26 ft. Question 15--Traffic Volume Threshold to · One county stated that they permit U-turns with a median Signalizing a Median Opening width between 20 and 24 ft and directional roadway width between 30 and 36 ft for a four-lane divided highway. 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 Question 13--Increase in U-Turning Vehicle Volumes When a Nontraversable Median is general MUTCD warrants for signalizing intersections. None Installed of the responding agencies presented any criteria for signaliz- ing median openings that differ from MUTCD signal warrants. 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 Question 16--Safety or Operational Problems at Unsignalized Median Openings (79 percent) responded that they had experienced an increase. Table B-20 summarizes the responses to this question. Question 16 asked highway agencies whether they had experienced safety or traffic operational problems at unsig- Question 14--Provision for School Buses, nalized median openings. Table B-22 shows the number and Other Buses, and/or Large Trucks percentage of highway agencies that indicated that they had experienced such problems at unsignalized median openings. Question 14 asked highway agencies whether their criteria Twenty-nine out of the 49 agencies that responded to this for design of median openings included provisions for school question (59 percent) indicated that they have encountered TABLE B-20 Number of agencies that have experienced an increase in U-turn volumes when a nontraversable median is installed 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 TABLE B-21 Number of agencies that make provisions for school buses, other buses, and large trucks in design of unsignalized median openings 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 TABLE B-22 Number of agencies that have encountered safety or operational problems at unsignalized median openings 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
OCR for page 101
B-12 safety or operational problems at unsignalized median open- · High number of accidents at median opening when road- ings. Table B-23 presents factors that the responding agen- way was converted from a two-lane to a four-lane facil- cies indicated were related to the safety or operational prob- ity (one agency) lems they encountered. Based on Table B-23, the five most cited factors that are related to safety or operational problems at unsignalized Question 17--Mitigation of Safety and median openings in decreasing order are: Operational Problems at Unsignalized Median Openings · Operational considerations (e.g., heavy U-turns or through volumes, trucks, etc) Question 17 asked highway agencies about mitigation · Median too narrow measures they had used in response to safety and operational · Driveway nearby problems at unsignalized median openings. Table B-24 pre- · Poor roadway geometry sents the number and percentage of agencies that have con- · Roadway too narrow structed improvement projects intended to mitigate safety and operational problems at unsignalized median openings. All factors presented in Table B-23 were cited by eight or Thirty-seven percent of the agencies stated that they had con- more agencies as contributing to safety or operational prob- structed such improvements. lems at unsignalized median openings. Some additional fac- Some of the mitigation measures for safety and opera- tors cited by the agencies include: tional problems cited are presented below: · High speed on approaches to median opening (one · Removal of closely spaced median openings by replac- agency) ing raised medians with TWLTLs (four agencies) · Excessive number of conflict points for crossing traffic · Replacement of conventional crossovers with directional (one agency) crossovers (two agencies) TABLE B-23 Factors identified by highway agencies as related to the safety or operational problems they encountered at unsignalized median openings Number of agencies Factors related to safety or operational State agencies Local agencies Total problems Yes No Yes No Yes No Operational considerations 10 0 10 7 20 7 (congestion, trucks) 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 5 4 7 8 12 12 area of an intersection Insufficient sight distance 6 3 5 10 11 13 Frequency/density of median 4 6 6 9 10 15 openings Median opening across from right-turn 3 7 1 14 4 21 lane 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-24 Number of agencies that have constructed improvement projects to mitigate safety or operational problems 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
OCR for page 102
B-13 · Installation of left-turn storage lanes (two agencies) might be suitable candidates for accident and field evaluation · Installation of left-turn lanes with positive offset (two later in this research. Table B-26 identifies the types of median agencies) openings that were identified by responding agencies as poten- · Signalize intersection (two agencies) tially available for evaluation. · Close median openings to allow left turns to align prop- erly (one agency) · Reconfigure median openings by channelizing or adding Question 19--Increase in U-Turn Volumes at left-turn lanes to prevent congestion or confusion in the Adjacent Median Openings Caused by the median opening (one agency) Installation of Raised Medians to Eliminate Direct Left-Turn Access to Intersections or · Installation of directional median openings to permit Driveways left turns from the major-road left-turn lane, but prohibit left turns and through movements from the minor road In Question 19, highway agencies were asked whether (one agency) they had experienced increases in U-turn volumes at median · Provide a median opening at what formerly was a right- openings, as a result of projects in which a raised median that in/right-out driveway (one agency) eliminated direct left-turn access to one or more intersections · Eliminate conventional median openings and replace or driveways was installed. Table B-27 shows that more than with jughandle U-turns (one agency) half of the responding agencies indicated that they had imple- · Installation of "No U-turn" signs (one agency) mented such projects recently (during the last 5 to 7 years) in · Installation of raised/extended median to prevent U-turns their jurisdiction. Ten state and 15 local agencies estimated (one agency) the approximate number of such projects; these estimates are presented in Table B-28. Table B-25 presents the number and percentage of agen- Table B-29 presents the number and percentage of state and cies that have conducted formal before-after evaluations of local agencies that encountered safety or operational prob- improvement projects that were constructed to mitigate the lems related to the installation of raised medians. Only three safety and operational problems at unsignalized median agencies indicated that they had encountered such safety or openings. Six agencies indicated that they have performed operational problems. Only one agency stated the type of such evaluations. problem which was that a small number of drivers made ille- gal U-turns or mounted the median to cross it. Question 18--Suitable Candidate Sites for The state and local agencies were asked if they have per- Accident and Field Evaluations formed any formal before-after evaluation of projects in which a raised median was installed which eliminated direct left- In Question 18, highway agencies were asked to identify turn access to intersection or driveways. Table B-30 summa- types of median openings under their jurisdiction and that rizes the responses to this question. Only one state indicated TABLE B-25 Number of agencies that have performed formal before-after evaluations of improvement projects at unsignalized median openings 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 TABLE B-26 Types of median openings that might be suitable candidates for accident and field evaluation Number of agencies Types of median openings that might be State agencies Local agencies Total 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
OCR for page 103
B-14 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 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 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 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 Average number of Agency type Number of agencies Total number of projects projects per agency State agencies 9 107 12 Local agencies 15 32 2 Total 24 139 7 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 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 TABLE B-30 Number of agencies that have performed formal before-after evaluations of projects involving raised medians 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 that they had performed such an evaluation. Table B-31 pre- openings were closed eliminating direct left-turn access to one sents the number of state and local agencies that indicated or more intersections or driveways, and resulting in increased that they have projects that may potentially be suitable for U-turn volumes at median openings elsewhere on the same evaluation as part of this research. A total of 13 agencies (four roadway. The responses to this question are summarized in state and nine local agencies) responded that they had poten- Table B-32. Thirty-seven percent of the agencies indicated tially suitable projects available. 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- Question 20--Closing of Existing Unsignalized mates are summarized in Table B-33. Median Opening Resulting in Increased U-Turn Volumes at Median Openings Elsewhere on the Table B-34 shows the number of agencies that had expe- Same Roadway rienced safety or operational problems resulting from proj- ects in which an existing unsignalized median opening was Question 20 asked highway agencies whether they had closed. It can be seen in the Table B-34 that only one state implemented projects in which existing unsignalized median answered that it had encountered such problems; this agency
OCR for page 104
B-15 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 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 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 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 TABLE B-33 Number of agencies and estimated number of projects that closed existing unsignalized median openings Number of agencies that Total number of Average number of Agency type have such projects projects projects State agencies 7 78 11 Local agencies 4 12 3 Total 11 90 8 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 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 did not specify the nature of the problem other than to say agencies indicated that they performed such evaluations. that it involved an increase in U-turns at other locations. Table B-36 summarizes the number of state and local agen- The responding state and local agencies were also asked if cies that have projects involving closure of unsignalized they have performed any formal before-after evaluations of median openings that may be suitable for evaluation as part projects in which an unsignalized median opening was closed. of this research. Nine agencies (five state and four local agen- Table B-35 summarizes the responses to this question. Three cies) indicated that they may have such projects. TABLE B-35 Number of agencies that have performed formal before-after evaluations of projects involving closure of an existing unsignalized median opening 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
OCR for page 105
B-16 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 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