Left-Turn Accommodations at Unsignalized Intersections (2013)

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30 Introduction This chapter includes 11 design examples and case studies, based on actual locations at which left-turn treatments were considered, evaluated, and/or installed. These case studies include: 1. Installation of exclusive left-turn lanes at an unsignalized intersection in a suburban fringe area. 2. Installation of an exclusive left-turn lane at an unsignalized intersection between a local street and a state highway. 3. Addition of a left-turn lane as part of a “road diet” treat- ment (conversion of a four-lane cross section to a three- lane cross section). 4. Installation of left-turn lanes at an unsignalized rural intersection between a state highway and a local road. 5. Installation of unsignalized “J-turn” intersections along a state highway. 6. Installation of a left-turn passing blister (i.e., bypass lane) at an unsignalized intersection between a local street and a state highway. 7. Installation of left-turn lanes at an unsignalized rural inter- section between a state highway and a county road. 8. Follow-up traffic studies to verify the need for an unsig- nalized left-turn lane in conjunction with a proposed development. 9. Installation of left-turn lanes at unsignalized intersections in conjunction with a proposed development. 10. Installation of an exclusive left-turn lane at an unsignal- ized suburban intersection between a state highway and a local street. 11. Installation of exclusive left-turn lanes and a traffic signal at an unsignalized intersection between a local street and a state highway. These design examples are intended to provide the practi- tioner with real-world scenarios that are similar to those the practitioner would actually encounter, along with possible solutions and the methods by which those solutions can be evaluated and installed. Design Application #1: Installation of Exclusive Left-Turn Lanes at an Unsignalized Intersection in a Suburban Fringe Area (Note: The intersection location in this design application has been made anonymous at the request of the contributing agency. Street names have been changed.) Context In a rapidly developing area, citizens are concerned with the number of cars using the shoulder to pass slow-moving left-turning vehicles on State Highway 41 (see Figure 13). The area is currently considered rural; however, the anticipated development within the next 5 years will change the per- formance of the roadway. Ultimately, State Highway 41 will provide more access and less mobility. It has already started evolving into a suburban high-speed arterial. Designers noted that the state’s Access Management Manual contains criteria on connection spacing for state highways. They decided to use the warrants developed as part of NCHRP Project 3-91 and the state’s Access Management Manual as part of their traffic operations evaluation, to determine whether a left-turn lane was appropriate at the intersection with David Drive. The intersection of State Highway 41 and David Drive is a T-intersection. The information known for this site includes: • State Highway 41 is a two-lane roadway. • Peak-hour turning-movement counts are shown in Figure 14. • The 85th percentile speed is 59 mph. • Posted speed is 55 mph. C h a p t e r 5 Design Examples

31 • Grades at the intersection are level. • Lane widths are 12 ft. • Shoulder widths on the major road are 10 ft. • No other left-turn bay is within 1 mile of the site. Design Considerations and Analysis Consideration of Turning and Through Volumes The primary consideration for the department of trans- portation (DOT) is the increasing volumes on the major highway, both turning and through movements. In this case, the peak-hour advancing volume from Figure 14 is (390 + 70) = 460 veh/hr, and the opposing volume is (288 + 34) = 322 veh/hr. The resulting overall volume on the major highway is (460 + 322) = 782 veh/hr, or 391 vehicles per hour per lane. Using Table 1 in Chapter 2, the designer can determine the recommended volumes for a left-turn lane on a rural high- way. The table is reproduced as Table 13, and the relevant volumes are highlighted. The peak-hour left-turn volume at this location is 70, which corresponds to the “50 or more” cat- egory in the table. For a two-lane rural highway intersection with three legs, the necessary peak-hour volume on the major highway is 50, which is less than the observed 391 shown in Figure 14. Therefore, a left-turn lane would be warranted at this location and should be considered. Since the location is on the edge of suburban development, designers could choose to use criteria for suburban arterials, which are provided in Table 2 in Chapter 2. That table is repro- duced here as Table 14 with the relevant volumes highlighted. For these conditions, with a peak-hour left-turn lane volume greater than 50 and a three-leg intersection, the necessary peak- hour volume on the major highway is 100, which is less than the observed volume of 391. Therefore, a left-turn lane would also be warranted at this location for suburban conditions. Consideration of Access Management Guidelines The state’s Access Management Manual lists spacing criteria for state highway system routes that are not new highways on Figure 13. Example of vehicle using shoulder to pass left-turning vehicle. Figure 14. Peak-hour turning- movement count. Left-Turn Lane Peak-Hour Volume (veh/hr) Three-Leg Intersection, Major Two- Lane Highway Peak-Hour Volume (veh/hr/ln) That Warrants a Bypass Lane Three-Leg Intersection, Major Two- Lane Highway Peak-Hour Volume (veh/hr/ln) That Warrants a Left-Turn Lane Four-Leg Intersection, Major Two- Lane Highway Peak-Hour Volume (veh/hr/ln) That Warrants a Bypass Lane Four-Leg Intersection, Major Two- Lane Highway Peak-Hour Volume (veh/hr/ln) That Warrants a Left-Turn Lane 5 50 200 50 150 10 50 100 < 50 50 15 < 50 100 < 50 50 20 < 50 50 < 50 < 50 25 < 50 50 < 50 < 50 30 < 50 50 < 50 < 50 35 < 50 50 < 50 < 50 40 < 50 50 < 50 < 50 45 < 50 50 < 50 < 50 50 or More < 50 50 < 50 < 50 Table 13. Recommended left-turn lane warrants for rural highways.

32 Left-Turn Lane Peak-Hour Volume (veh/hr) Three-Leg Intersection, Major Urban and Suburban Arterial Volume (veh/hr/ln) That Warrants a Left-Turn Lane Four-Leg Intersection, Major Urban and Suburban Arterial Volume (veh/hr/ln) That Warrants a Left-Turn Lane 5 450 50 10 300 50 15 250 50 20 200 50 25 200 50 30 150 50 35 150 50 40 150 50 45 150 < 50 50 or More 100 < 50 Table 14. Recommended left-turn lane warrants for urban and suburban arterials. Table 15. Minimum spacing criteria for access connections. Posted Speed (mph) Distance (ft) ≤ 30 200 35 250 40 305 45 360 ≥ 50 425 new alignments. The relevant information is reproduced in Table 15, and it shows that, with a posted speed in excess of 50 mph, the spacing distance is 425 ft. A turn bay for another intersection or driveway is currently not present within that distance. Design Result A driveway is present approximately 300 ft west of the inter- section. The design team decided to move forward with the turn lane at the intersection and to inform the property owner that a median opening at the driveway would not be consid- ered when the highway is widened. Design Application #2: Installation of an Exclusive Left-Turn Lane at an Unsignalized Intersection Between a Local Street and a State Highway Context Laurel Drive is a two-way, east-west local street, approxi- mately 800 ft long, which provides access to several abutting properties including a church and several parcels accom- modating office/light-industrial uses. The east end of Laurel Drive terminates at a cul-de-sac that accommodates separate driveways serving two properties. To the west, Laurel Drive terminates at an unsignalized T-intersection with Route 206. The Laurel Drive approach is stop controlled. Route 206 is a key north-south state highway through the area that wid- ens immediately south of Laurel Drive to accommodate two continuous through lanes in the northbound direction and one continuous through lane in the southbound direction (see Figure 15). The posted speed on Route 206 is 45 mph. The intersection is located in a developing, suburban area that includes many large undeveloped parcels. Properties along the west side of Route 206 in the vicinity of Laurel Drive are currently undeveloped. Design Request The Mount Olive Township Police Department contacted the New Jersey Department of Transportation (NJDOT) with respect to the unsignalized intersection of Laurel Drive/Route 206, noting it as a safety concern due to a recent serious crash as well as many near misses. The intersection was noted as accommodating relatively high traffic volumes associated with employees and trucks traveling through the intersection to and from the abutting office/industrial uses. Representatives from the police department suggested NJDOT consider poten- tial measures to improve the safety performance at this inter- section. Improvements to the intersection were supported in writing by a signed petition from more than 130 employees from one of the tenants on a property abutting Laurel Drive. Subsequent investigations by NJDOT staff revealed that there were nine crashes at the intersection in the most recent 3-year period for which data were available. Of these nine crashes, at least five appeared to be of a type that could poten- tially be mitigated by installation of an exclusive left-turn lane in the southbound direction. In addition, investigations by NJDOT indicated that installing an exclusive southbound left-turn lane would not interfere with the traffic flow on Route 206, yet would provide refuge for southbound vehicles turning left from Route 206 onto Laurel Drive.

Figure 15. Laurel Drive/Route 206 intersection: existing condition. Figure 16. Laurel Drive/Route 206 intersection: proposed condition.

34 Design Considerations and Analysis The primary design considerations evaluated by NJDOT included the existing traffic operations and safety characteris- tics of the intersection. In this particular instance, right-of- way and budgetary limitations eliminated the prospect of additional widening on Route 206, such that the addition of the left-turn lane needed to be accommodated within the existing pavement width along Route 206. Fortunately, despite these constraints, the intersection is located at a point where Route 206 widens from one lane to two lanes in the north- bound direction. Therefore, the southbound left-turn lane on Route 206 was designed to be accommodated on exist- ing pavement that formed the westerly travel lane, north of the intersection. Specifically, NJDOT addressed the following items as part of the design: • Determine the length of left-turn queue storage. Multiple field visits to the site during various times determined that a 100-ft storage length for the left-turn lane would be ade- quate to accommodate expected vehicle queues. NJDOT also solicited input from the police department in deter- mining the length of the left-turn storage lane. The police department concurred with the 100-ft length. • Determine the length of the shifting taper. The length of the shifting taper on the upstream approach (“L”) was cal- culated by NJDOT as: L WS= 2 where W = transition width (12 ft) and S = speed in mph (45 mph). Consequently, L = 270 ft. • Determine the length of the downstream taper. The downstream taper is intended to transition the cross section from one to two northbound lanes, north of Laurel Drive, beyond the left-turn lane. A downstream taper length of 100 ft—the MUTCD minimum for urban areas—was used by NJDOT. • Determine cross-sectional lane widths. According to the New Jersey design manual, it is preferable to provide 12-ft standard lanes where possible. Because there was suffi- cient pavement width to accommodate 12-ft standard lane widths, the decision was made to apply the standard lane widths. Design Result Figure 16 illustrates the final design configuration with implementation of the exclusive southbound left-turn lane on Route 206. This improvement is planned for implementa- tion in the near future. Design Application #3: Addition of a Left-Turn Lane as Part of a “Road Diet” Treatment (Conversion of a Four-Lane Cross Section to a Three-Lane Cross Section) Context Titus Avenue is a four-lane east-west roadway approxi- mately 3.2 miles long, located north of the City of Rochester, New York. Titus Avenue is classified as a minor arterial, has a posted speed of 35 mph, and is abutted by a mix of suburban commercial and residential development. Multilane county highways like Titus Avenue, due for major maintenance or reconstruction involving resurfacing and restriping, are peri- odically evaluated by Monroe County engineering staff to see if a multilane conversion (road diet) would be appropriate. This conversion involves changing the cross section of multi- lane highways to accommodate one travel lane in each direc- tion, and converting the excess pavement width into auxiliary lanes (e.g., left-turn lanes, right-turn lanes, and/or shoulders) to realize the safety and traffic-calming benefits of such fea- tures. As part of the conversion project along Titus Avenue, a left-turn lane was provided on the westbound Titus Ave- nue approach at the unsignalized intersection with Seneca Avenue. Design Request As part of the Monroe County road diet program, engineer- ing staff considered converting Titus Avenue from a four-lane cross section to a three-lane cross section. The cross section along Titus Avenue accommodated four 11-ft travel lanes, two in each direction. The cross section of Titus Avenue at the unsignalized intersection with Seneca Avenue is shown in Fig- ure 17. Seneca Avenue is a major north-south collector road- way that serves a predominately residential neighborhood and terminates to the north at Titus Avenue. The posted speed on Seneca Avenue is 35 mph. Design Considerations and Analysis In general, the primary design considerations that were eval- uated by Monroe County engineering staff included: • Traffic volume, • Safety, • Signalized intersection capacity, • Signal spacing, and • Potential future roadside development.

35 Specifically, Monroe County considers roadways with the following characteristics to be good candidates for road diets: • Four travel lanes with peak directional traffic volumes that could be accommodated by one travel lane in each direction, • A record of crash patterns correctable by the implementa- tion of left-turn lanes, • Signalized intersections that would maintain adequate capacity following the road diet conversion, • No closely spaced signals, and • Low potential for future roadside development. With respect to the characteristics above, Titus Avenue was considered for a road diet based on its cross section (four travel lanes) and its peak directional traffic volume of approximately 260 vehicles per hour per lane (veh/hr/ln), which could be accommodated by one travel lane in each direction. This peak-hour directional volume is below the 450 veh/hr/ln threshold used by Monroe County for consid- eration in road diets. The road diet was implemented along a section of Titus Avenue away from closely spaced signal- ized intersections, and with low potential for future roadside development. The abutting properties were fully developed, and few land use changes were expected over time. For most of the length of the road diet on Titus Avenue, the left-turn treatment consists of a center two-way left-turn lane (TWLTL) to accommodate vehicles turning left into the residences and suburban commercial establishments abut- ting the roadway. However, because Seneca Avenue is a key collector-level roadway that intersects Titus Avenue only from the south, an exclusive left-turn lane was striped on the westbound approach to accommodate left turns onto Titus Avenue. Design Result The final, improved cross section on Titus Avenue accom- modates one 11-ft travel lane in each direction, one 12-ft center TWLTL, and 5-ft shoulders on both sides of the road. Figure 18 illustrates the final, improved configuration of the unsignalized Titus Avenue/Seneca Avenue intersection, with implementation of the three-lane road diet. In 2009, a peak-hour directional volume of 315 veh/hr/ln was counted, suggesting that traffic volumes have continued to remain at a level easily accommodated by one travel lane in each direction. In addition, reportable crash rates were found to have decreased when comparing the 2 years (2002 to 2003) just prior to the road diet, to the 3 years (2005 to 2007) fol- lowing the road diet. Design Application #4: Installation of Left-Turn Lanes at an Unsignalized Rural Intersection Between a State Highway and a Local Road [Note: The intersection location in this design application has been made anonymous at the California Department of Transportation’s (Caltrans’) request. Street names have been changed.] (Source: Pictometry International, 2001 Markup credit: Monroe County Department of Transportation, New York, 2010. Used by permission.) Se ne ca A ve nu e N Titus Avenue Figure 17. Titus Avenue/Seneca Avenue intersection: previous four-lane cross section. Se ne ca A ve nu e Titus Avenue N (Source: Pictometry International, 2009 Markup credit: Monroe County Department of Transportation, New York, 2010. Used by permission.) Figure 18. Titus Avenue/Seneca Avenue intersection: final three-lane cross section.

36 Context Franklin Avenue is a two-way, east-west local road located in a predominately rural area in central California. It accom- modates one 12-ft travel lane in each direction, with no paved shoulder, and has a posted speed of 55 mph. Franklin Avenue intersects State Route (SR) 47 at an approximate 90-degree angle forming a four-legged, unsignalized intersection. SR 47 is a two-way, north-south highway that extends from the Pacific coast through central California. In the vicinity of Franklin Avenue, SR 47 has a posted speed of 55 mph and accommodates one 12-ft travel lane and an 8-ft shoulder in each direction. At the Franklin Avenue/SR 47 intersection, only the east- bound and westbound (Franklin Avenue) approaches are stop controlled. No exclusive turn lanes are provided along either roadway. All four quadrants of the intersection are used for agricultural purposes, though a major casino/hotel complex is located approximately 1,600 ft east of the intersection on the south side of Franklin Avenue. Figure 19 illustrates pre- project conditions at the Franklin Avenue/SR 47 intersection. Design Request An investigation of this intersection was triggered by the Caltrans monitoring system, which reported this intersection as a location with a high concentration of crashes. The crash history at this intersection over the 36-month time period between April 1, 1998, and March 31, 2001, revealed six crashes that involved motorists passing stopped vehicles that were waiting to make left turns onto Franklin Avenue. Design Considerations and Analysis A detailed analysis was initiated by Caltrans’ Traffic Investi- gations Unit that included a safety review. After analyzing the crash patterns and conducting a field review, the unit deter- mined that left-turn lanes should be installed on the north- bound and southbound (SR 47) approaches to help improve safety at the intersection. Caltrans addressed the following items as part of the design of the left-turn lanes. Determine the Approach Taper Length Section 405.2(2)(b) of the Caltrans Highway Design Man- ual (29) provides the following design guidance for calculat- ing the length of the approach taper on highways with speeds of 45 mph or more: L WV= where: L = length (ft) W = lateral offset (ft) V = speed (mph) The Franklin Avenue/SR 47 intersection has a posted speed of 55 mph, and a lateral offset of 12 ft was desired. Therefore, the approach taper length for the left-turn lanes on SR 47 was calculated as follows: L ft= × =12 55 660 Determine the Bay Taper Length Section 405.2(2)(c) of the Caltrans Highway Design Man- ual (29) provides the following design guidance for calculat- ing the length of the bay taper: In urban areas, (bay taper) lengths of 60 ft and 90 ft are normally used. . . . On rural high-speed highways, a 120-ft length is con- sidered appropriate (for the bay taper). Because the intersection with Franklin Avenue is located along a rural, high-speed section of SR 47, a 120-ft bay taper was used. Determine the Deceleration Length Section 405.2(2)(d) of the Caltrans Highway Design Manual (29) provides the following design guidance for calculating the deceleration length: Deceleration Lane Length—Design speed of the roadway approaching the intersection should be the basis for determining Figure 19. Franklin Avenue/SR 47 intersection: pre-project configuration. (Source: Caltrans. Used by permission.) FR A N K LI N A V EN U E N TO C A SI N O STATE ROUTE 47

37 deceleration lane length. It is desirable that deceleration take place entirely off the through traffic lanes. Deceleration lane lengths are given in Table 405.2B; the bay taper length is included. Where partial deceleration is permitted on the through lanes . . . design speeds in Table 405.2B may be reduced 10 mph to 20 mph for a lower entry speed. Table 405.2B of the Caltrans Highway Design Manual is reproduced in this guide as Table 16. Partial deceleration was used (as permitted by the Caltrans Highway Design Manual) with a speed reduction of 10 mph from the posted speed limit of 55 mph (i.e., 45 mph). Inter- polation from Table 405.2B of the Highway Design Manual resulted in a total deceleration length of 375 ft. Determine the Queue Storage Length Section 405.2(2)(e) of the Caltrans Highway Design Man- ual (29) provides the following design guidance for calculat- ing the queue storage length at unsignalized intersections: At unsignalized intersections, storage length may be based on the number of turning vehicles likely to arrive in an average 2-minute period during the peak hour. As a minimum, space for 2-passenger cars should be provided at 25 ft per car. If the peak hour truck traffic is 10 percent or more, space for one passenger car and one truck should be provided. Because this highway segment accommodates 16 percent truck traffic, one truck length (i.e., 75 ft) plus one passenger car length (i.e., 25 ft) were used to calculate the 100-ft storage distance. Determine Left-Turn Lane Width A 12-ft lane was used, as per the Caltrans Highway Design Manual (29), Section 405.22a, which states that the lane width for both single and double left-turn lanes on state highways shall be 12 ft. Design Result Figure 20 illustrates the final design configuration of the Franklin Avenue/SR 47 intersection with implementation of northbound and southbound left-turn lanes on SR 47. Right- of-way was acquired from parcels on the northeast, southeast, and southwest corners to accommodate the widening. Post-project crash data for the time period between July 1, 2007, and December 31, 2008, suggest that the previous pat- tern of passing/left-turn collisions was mitigated by installa- tion of the left-turn lanes on SR 47. Design Application #5: Installation of Unsignalized “J-Turn” Intersections Along a State Highway Context US 15 is a two-way, rural principal arterial following a north- south alignment across Maryland from the Pennsylvania bor- der to the Virginia border. US 15 is not only a heavily used commuter route for local and regional traffic, but also serves as a major north-south highway route on the East Coast, accom- modating traffic from New York State to South Carolina. Access control along the entire interstate length of US 15 ranges from fully access-controlled freeway segments with grade-separated interchanges, to partially access-controlled expressway seg- ments with at-grade intersections. The subject section of US 15, located between MD 26 and the Pennsylvania border in Frederick County, is a four-lane divided highway with two 12-ft lanes in each direction, plus a 4-ft median shoulder and a 10-ft right shoulder. The direc- tional roadways are separated by a wide grass median that varies in width from 51 ft to 72 ft. Full-access at-grade median breaks are provided at intersections with major public roads. These intersections are generally spaced several thousand feet apart, and have separate exclusive left-turn and right-turn lanes on US 15. The speed limit in this section of US 15 is 55 mph, Design Speed (mph) Length to Stop (ft) 30 235 40 315 50 435 60 530 Table 16. Deceleration lane length for left-turn lanes (29). (Source: Caltrans. Used by permission.) TO C A SI N O FR A N K LI N AV EN U E N STATE ROUTE 47 Figure 20. Franklin Avenue/SR 47 intersection: post-project configuration.

38 with 85th percentile speeds in the 60 to 65 mph range. Trucks account for approximately 15 percent of the vehicle mix in the traffic stream. Design Request In the 1970s and 1980s, Frederick County began to expe- rience significant residential and commercial growth, which continues today, making it one of the fastest growing counties in Maryland. During the 1980s and 1990s, average daily traf- fic (ADT) volumes along US 15 were observed to increase at a rate of 7 percent annually. Traffic volumes—particularly left turns to and from US 15 and the intersecting side streets— also increased at most intersections, increasing the pressure for traffic signal installations. These turns also generated an increase in angle-type crashes. In addition, the transitions in design elements between the freeway and expressway seg- ments along US 15 were a safety concern to the Maryland State Highway Administration (MDSHA) because these changes tend to violate driver expectancy and lessen driver awareness and responsiveness. Although there are long-range plans to convert US 15 into a freeway with fully controlled access, interchanges, and service roads, MDSHA had no immediate plans to provide such improvements along the subject por- tion of US 15. MDSHA also developed the position, with the full coop- eration and support of Frederick County government, that traffic signals would not be placed at any location along the subject section of US 15, even where warranted by the Manual on Uniform Traffic Control Devices. MDSHA was concerned, based on past experiences at other similar locations, that the mixing of freeway and expressway design elements, high traf- fic volumes, and high speeds would create overly hazardous conditions with the potential for serious rear-end and angle crashes. These concerns, coupled with the rapid traffic growth and increasing crash trends along the subject segment of US 15, led MDSHA to consider application of the “directional crossover” concept—also known as a “J-turn” or “superstreet.” Design Considerations and Analysis A variety of other potential design treatment options were considered to address the safety and operational issues along the subject segment of US 15, including the following: • Installation of traffic signals was not selected due to concerns that the crash experience, particularly in terms of severity, would likely increase. • Complete crossover closure was not selected because it was MDSHA’s intent to only (initially) prohibit the prob- lem movement (i.e., left turns), while still allowing a high level of access to and from the side streets. • Installation of jug handles was ruled out because the jug handle intersection treatment would not eliminate through and left-turn movements from the side streets, and would require signalization. Ultimately, MDSHA selected the J-turn as the preferred treatment along the subject segment of US 15. Figure 21 is an aerial photograph of an existing (signalized) J-turn location in Troy, Michigan, illustrating the typical geometric configu- ration of the J-turn treatment (30). The primary purpose of the J-turn treatment is to elim- inate the left turns and through movements from the side street. As shown in Figure 21, this is accomplished by install- ing a raised channelizing island within the median crossover at the subject intersection as well as channelizing islands on the side-street approaches, such that only right turns to and from the side street and left turns from the major street to the side street are allowed. Motorists desiring to make left turns and through movements from the side-street approaches must make these movements indirectly, via a right turn from the side street, followed by a U-turn at a median break located downstream of the subject intersection. The J-turn configuration can negate the need for signalization at the subject intersection, eliminates the cause of most angle col- lisions (i.e., left-turn and through movements), significantly reduces the number of conflict points, and reduces the poten- tial for confusion among drivers turning within the median crossover. The intersections of the following roads, located along the subject segment of US 15, were selected by MDSHA for the J-turn treatment: • College Lane, • Old Frederick Road, • Sundays Lane, • Biggs Ford Road, • Willow Road, • Monocacy Boulevard, and • Hayward Road–MD 355. Figure 21. Aerial photograph of typical J-turn intersection treatment (30). (Source: Google Earth™ mapping service.)

39 This design application focuses on the J-turn treatment at the intersection of College Lane and US 15. In the vicinity of College Lane, US 15 bisects the campus of Mount Saint Mary’s University, just south of Emmitsburg, Maryland. College Lane serves as the primary access to the main campus located west of US 15, and to Knott Arena and the athletic complexes located east of US 15. In addition to traffic volumes at the intersection that nearly met traffic signal warrants under normal weekday conditions, Knott Arena generated high volumes of traffic on nights and weekends as a result of sporting/special events. These volumes became so high that university officials manu- ally directed traffic at the intersection. Working closely with the university, MDSHA constructed a J-turn intersection treatment at the intersection in August 1994. The treatment included two U-turn crossovers on US 15, located approximately 2,000 ft south and 3,000 ft north of College Lane. Design Result Figure 22 illustrates the final design configuration at the College Lane/US 15 intersection with implementation of the J-turn treatment. A before study of the College Lane/US 15 intersection’s crash history prior to the J-turn improvement revealed that 11 crashes occurred during the 3-year period between August 1991 and July 1994. These crashes included nine angle crashes, 8 injury crashes, and 19 personal injuries. During the 3-year after study period from September 1994 through August 1997, following construction of the J-turn, there was only one reported crash, which was a left-turn collision that resulted in two injuries. Furthermore, there were no reported crashes during the after period at the U-turn crossovers located on US 15 north and south of College Lane. MDSHA’s experiences with the J-turn intersection treat- ment have revealed several important design considerations: • Provide adequate sight distance for major-street left turns. The proper alignment of the major-street left-turn lanes within the median is crucial to maintaining adequate sight distance for drivers making these turns. Vehicles mak- ing left turns from the major street should be aligned such that drivers’ sight lines to oncoming through traffic are not obstructed by vehicles queued in the opposing left-turn lane. • Provide “loons” for large U-turning vehicles at down- stream median breaks. It is important that vehicles with large turning radii (e.g., tractor-trailers) are able to com- plete the U-turn maneuver at the downstream median breaks without tracking beyond the edge of pavement. To accommodate these large-radius turns, particularly along corridors with narrow medians, extra widening of the pave- ment beyond the normal shoulder (i.e., “loons”) should be installed to accommodate such vehicles. • Provide adequate distance to the downstream median break. As noted previously, drivers desiring to make left turns and through movements from the side-street approaches must make these movements indirectly, via a right turn from the side street, followed by a U-turn at a median break located downstream of the subject intersection. These drivers must be provided with enough distance between the intersection and the downstream U-turn median break to safely merge with, and across, major-street traffic in order to turn into the median break. However, as traffic volumes on the major street increase over time, and the number of available gaps in the traffic stream decreases, this maneuver can become more difficult. Therefore, it is important that future traffic growth along the major street in both directions be considered in the design. MDSHA’s experience has shown that a separation distance of 1,700 ft was sufficient for roadways with aver- age annual daily traffic (AADT) volumes of approximately 20,000 vehicles per day. However, as the AADT on the same roadway increased to approximately 43,000 vehicles per day, a separation distance of 3,000 ft was desirable. Design Application #6: Installation of a Left-Turn Passing Blister at an Unsignalized Intersection Between a Local Street and a State Highway (Note: The intersection location in this design application has been made anonymous at the request of the contributing agency. Street names have been changed.) (Source: Google Earth™ mapping service.) College Lane US 15 N Figure 22. College Lane/US 15 intersection: final J-turn configuration.

40 Context Sherwood Road is a two-way, east-west local street that pro- vides access to a rapidly developing industrial park area that currently includes a furniture store and a major distribution center for a fast-food restaurant chain. The 1997 AADT on Sherwood Road was 1,950 vehicles per day, but daily and peak- hour volumes are expected to increase significantly in the future as a result of intensifying operations for the existing industrial uses along Sherwood Road, and anticipated new developments in the industrial park. Sherwood Road has a posted speed of 30 mph and is aligned within an existing right-of-way of approximately 40 ft. Sherwood Road terminates to the west at an approximate 65-degree T-intersection with SR 46. State Road 46 (SR 46) is a two-way, north-south state high- way with a 1997 AADT of 8,460 vehicles per day and a posted speed of 50 mph. SR 46 is classified as a rural principal arterial and is the primary north-south highway through the region. In the vicinity of Sherwood Road, SR 46 has an approximate 60-ft right-of-way. The Sherwood Road/SR 46 intersection is unsignalized, and only the Sherwood Road (westbound) approach is stop controlled. Both roadways accommodate one 12-ft travel lane in each direction. No turn lanes or shoulders have been con- structed along either roadway. There is adequate intersection sight distance in both directions. Design Request Both the local chamber of commerce and the local police department contacted the state department of transporta- tion to request that the unsignalized Sherwood Road/SR 46 intersection be investigated for possible improvements. In the correspondence, they noted the large amount of recent— and anticipated future—traffic growth at the intersection associated with the expanding industrial park. In addition, they noted that the increasing traffic volumes are exacerbat- ing safety issues, resulting in several crashes and near misses, including one crash that resulted in a fatality. Design Considerations and Analysis In response to these local requests, a comprehensive and detailed investigation of traffic operations and safety was con- ducted by state transportation engineering staff. The study found high peak-hour volumes of passenger vehicles during time periods of worker shift changes, as well as a relatively high percentage of trucks traveling through the intersection. Although the number of crashes occurring during the most recently available 3-year period was not particularly high, the fatality indicated that the intersection should receive priority treatment. The design considerations evaluated by staff included the existing and projected future traffic operations and safety characteristics of the intersection. The following is a listing of the primary improvements staff recommended for imple- mentation at the Sherwood Road/SR 46 intersection, based on their analysis findings: • Construct a left-turn passing blister on the west side of SR 46 in the vicinity of Sherwood Road to allow southbound through vehicles to bypass vehicles making a southbound left turn onto Sherwood Road. • Construct a northbound right-turn lane. • Widen the Sherwood Road (westbound) approach to accom- modate separate exclusive left-turn and right-turn lanes at the intersection. • Construct shoulders on both SR 46 and Sherwood Road. Staff determined that additional right-of-way was needed to accommodate the improvements above. The width of the additional right-of-way acquisition varied from approxi- mately 20 to 30 ft. The state’s design manual provides guidelines for various left-turn treatments (i.e., left-turn lanes, left-turn passing blis- ters, etc.). The following sections were referenced as part of the design of the left-turn passing blister: • Determine the type of left-turn treatment on the southbound approach of SR 46. As stated in the design manual: At some three-legged intersections, it may be desirable to provide a passing blister to relieve congestion due to left-turning vehicles . . . Passing blisters may be provided at the intersection of all pub- lic roads and streets on 2-lane State highways with a design year ADT of 5000 or greater . . . The decision on whether to use either a channelized left-turn lane or a passing blister will be based on accident history, right-of-way availability, through and turn- ing traffic volumes, design speed and available sight distance. A channelized left-turn lane should be provided if the left-turn volumes are high enough that a left-turn lane is warranted . . . • Determine the length of the passing blister and associated tapers. The length of the passing blister, and the associ- ated upstream and downstream tapers, are based on speed as described in the state’s manual, shown here as Table 17. Because the posted speed on SR 46 is 50 mph, the minimum length of the passing blister was determined to be 197 ft. Staff selected a length of 328 ft for use in the design. The mini- mum length of both tapers was determined to be 295 ft (see Table 17) and these lengths were incorporated into the design. Design Result Figure 23 illustrates the final design configuration of the Sherwood Road/SR 46 intersection with implementation of

41 the southbound left-turn passing blister on SR 46 and other improvements. Construction of this improvement was com- pleted in 2005. Design Application #7: Installation of Left-Turn Lanes at an Unsignalized Rural Intersection Between a State Highway and a County Road (Note: The intersection location in this design application has been made anonymous at the request of the contributing agency. Street names have been changed.) Context County Road 800 North (CR 800N) is a two-way, east-west county highway through a rural area. CR 800N is classified as a rural minor collector and accommodates one 11-ft lane, plus a 6-ft shoulder, in each direction. The 1997 AADT on CR 800N was 1,040 vehicles per day, of which approximately 10 percent were commercial vehicles. CR 800N has a posted speed of 45 mph and intersects US 281 (a state highway) at an approxi- mate 90-degree angle, forming a four-legged intersection. The existing right-of-way along CR 800N is 33 ft. US 281 is a two-way highway that extends north-south across nearly the entire state. It is classified as a rural princi- Figure 23. Sherwood Road/SR 46 intersection: post-implementation condition. Design Speed, vD (mph) T1 (ft) L (ft) T2 (ft) ≤ 31 148 148 148 31 < vD < 50 197 148 197 ≥ 50 295 197 295 NOTES: “T1” and “T2” are the minimum lengths of the upstream and downstream tapers, respectively; and “L” is the minimum length of the passing blister. • • Table 17. Minimum dimensions for passing blisters on two-lane highways for design application #5.

42 pal arterial and had a 1997 AADT of 8,400 vehicles per day, of which approximately 13 percent were commercial vehicles. US 281 has a posted speed of 55 mph and accommodates one 12-ft travel lane, plus a 4-ft shoulder, in each direction. From a regional perspective, US 281 serves as a major north-south highway route through the state. In the vicinity of CR 800N, US 281 has right-of-way that varies from 40 to 70 ft. The US 281/CR 800N intersection is unsignalized, and only the CR 800N (eastbound and westbound) approaches are stop controlled. No turn lanes are provided along either roadway. All four quadrants of the intersection are used for agricultural purposes, although development in the area is expanding, and the southwest quadrant was subdivided for residential housing. Design Request The need for improvements at the US 281/CR 800N inter- section was reported to state department of transportation staff in a district office by local citizens who noted several crashes in the northbound direction and increased traffic vol- umes associated with development in the area. Design Considerations and Analysis An engineering investigation of traffic operations and safety at the US 281/CR 800N intersection was conducted by state transportation engineering staff in the district office. A review of crash data for the 4-year period from 1993 through 1996 revealed that of the eight crashes that occurred during this time, four (50 percent) were rear-end crashes. These rear- end crashes resulted in a total of five injuries to vehicle occu- pants. In addition, the state’s investigation revealed delays for northbound and southbound through traffic when north- bound and southbound left-turning vehicles were present and waiting to turn. Because the need for an improvement was particularly acute in the northbound direction, staff initially recommended that a northbound “passing blister” (i.e., pave- ment widening to accommodate through traffic traveling to the right of left-turning vehicles) be installed. However, based on a field visit by the design team (i.e., including district staff and consultants), it was agreed that opposing left-turn lanes on both the northbound and southbound approaches would pro- vide improved intersection geometrics and a more smooth lane transition for through traffic for only a small incremen- tal increase in cost. Based on the findings of this investiga- tion, state staff recommended implementing left-turn lanes in both the northbound and southbound directions on US 281 at its intersection with CR 800N. Staff determined that additional right-of-way was needed along US 281—as well as a small amount along CR 800N—to accommodate the left- turn lanes. The state’s design manual provides warrants for determin- ing whether an exclusive left-turn lane is needed. In addition, the state design manual provides the following guidance for determining the lengths for deceleration (LD), taper (LT), and queue storage (LS) for left-turn lanes: The length of auxiliary lanes will be determined by some com- bination of its taper length (LT), deceleration length (LD) and storage length (LS) and by the mainline functional classifica- tion. Length considerations for the various classifications are as follows: Classification Functional Length Rural arterials L T + LD + LS Urban arterials and other facilities L T + LD + LS (Desirable) Stop or t facilities L T + LS NOTE: LT = length of taper (100 ft or more) LD = length of deceleration (only a consideration at free- flowing legs of stop-controlled intersections, at signal- ized intersections, and at free-flowing turning roadways with turn lanes) LS = length of storage The following will apply. 1. Taper. For tangent approaches, the department’s practice is to use a 100-ft straight-line taper at the beginning of a single turn lane. . . . 2. Deceleration. For rural facilities, the deceleration distance (LD) should meet the criteria presented in Table 18. In addition, the values determined from Table 18 should be adjusted for grades. Table 18 also provides these grade adjustment factors. These distances are desirable on urban facilities; however, this is not always feasible. Under restricted urban conditions, deceleration may have to be accomplished entirely within the travel lane. For these cases, the length of turn lane will be determined solely on the basis of providing adequate vehicle storage (i.e., LD = 0.0 m). 3. Storage Length (Signalized Intersections) [DOES NOT APPLY] 4. Storage Length (Unsignalized Intersections). The storage length should be sufficient to avoid the possibility of left- turning vehicles stopping in the through lanes and waiting for a gap in the opposing traffic flow. The minimum stor- age length should have sufficient length to accommodate the expected number of turning vehicles likely to arrive in an average 2-minute period within the design hour. At a mini- mum, space should be provided for two passenger cars. If truck traffic exceeds 10 percent, space should be provided for at least one passenger car and one truck. The recom- mended storage lengths for right- and left-turn lanes at unsignalized intersections are provided in Table 19. Based on the guidance for taper, a left-turn taper of 100 ft was provided on both the northbound and southbound approaches on US 281. In order to avoid an excessive project

43 length, deceleration lengths were not planned for the left-turn lanes due to the relatively low volume of left-turn movements and the available sight distance along this section of US 281. The storage lengths for the northbound and southbound left- turn lanes (i.e., approximately 98 ft) were identified based on projected future design volumes of northbound and south- bound left-turning traffic. Design Result Figure 24 illustrates the final design configuration of the US 281/CR 800N intersection with implementation of north- bound and southbound left-turn lanes on US 281. Design Application #8: Follow-Up Traffic Studies to Verify the Need for an Unsignalized Left-Turn Lane in Conjunction with a Proposed Development Context SR 542 is a two-way east-west state highway located in cen- tral Florida. Within the city of Winter Haven, SR 542 is also known as Dundee Road and is classified as an arterial. SR 542 accommodates one travel lane in each direction, has a posted speed of 55 mph, and had an ADT of 16,900 vehicles per day (vpd) in 2004. Design Request In 2004, the Florida Department of Transportation (FDOT) received an access permit request associated with the pro- posed development of a 15,784-square-ft outpatient sur- gery center on the south side of SR 542, east of Florida Drive, in Winter Haven. As part of this development, two full-access, stop-controlled private driveways were pro- posed to connect to the south side of SR 542, approximately 300 ft east and 900 ft east of Florida Drive, respectively. The second driveway was proposed by the applicant as part of the initial application in anticipation of a second develop- ment phase occurring on the site as part of a planned future expansion. Design Considerations and Analysis As part of the access permitting process, FDOT’s access management specialists reviewed the proposed develop- ment plans and concluded that widening of SR 542 would be required to accommodate a westbound left-turn lane at the westerly site-access driveway. FDOT reached this conclusion based on: • A review of existing traffic volumes and projected future traffic growth along SR 542; • Trip generation estimates for the proposed development, based on standard trip rates from ITE; and • FDOT’s assumed trip distribution characteristics (east/ west split) for the proposed development. Turning DHV (veh/hr) LS (ft) < 60 61–120 121–180 >180 50–80 100 150 200 or greater NOTES: “DHV” is the design hourly volume. “L • • S” is the minimum storage length for the left-turn lane. Table 19. Recommended storage lengths (LS) for unsignalized intersections. Design Speed (mph) Desirable LD Full-Width Auxiliary Lane (ft) 70 65 60 55 50 45 40 35 944 850 756 662 567 473 379 284 Grade Adjustment Factors Downgrade 6.00 to 5.00% 4.99 to 4.00% 3.99 to 3.00% 2.99 to 2.01% 2.00 to 0% 1.35 1.28 1.20 1.10 1.10 Upgrade 0 to 2.00 % 2.01 to 2.99% 3.00 to 3.99% 4.00 to 4.99% 5.00 to 6.00% 1.00 0.95 0.90 0.85 0.80 NOTE: Multiplying the length LD by the grade adjustment factor will give the deceleration lane length adjusted for grade. Adjustment factors apply to all design speeds. Table 18. Deceleration distances for turning lanes.

44 However, the applicant disputed the use of ITE trip genera- tion rates, noting that the proposed surgery center would have unique operational characteristics, quite unlike the traditional medical/dental office uses reflected in the ITE database. In par- ticular, the applicant noted that the surgery center would have: • No patient examinations, check-ups, or follow-up appointments; • No prescription refills; • No visits by nurse practitioners or other assistants; • An average patient stay of 4 hours (longer than that sug- gested by ITE); and • Patients arriving for purposes of surgery only and leaving the facility by the early afternoon. The applicant contended that these unique operational characteristics would result in vehicle trip generation at the proposed site that would be lower than that calculated using ITE rates, such that the threshold for installation of a left- turn lane on SR 542 would not be met. In addition, there was a dispute about the trip distribution pattern assumed by the applicant. FDOT projected that more site-generated traffic would be oriented to and from the east, given the proximity of the site to US 27, a major north-south state highway located approximately 3.25 miles east of the site. Design Result Given the circumstances of this particular access permit application and uncertainties surrounding the operational aspects of the proposed use, FDOT and the applicant reached a compromise: FDOT agreed to grant a conditional access per- mit without requiring construction of the westbound left-turn lane, provided that the applicant supplied FDOT with a bond for the construction cost of the left-turn lane. Furthermore, after the proposed surgery center was open and operational for 1 month, the applicant would be obligated to conduct a follow-up traffic study—based on actual field conditions and mutually agreed-upon criteria—to reassess whether or not the left turn would be warranted. If the left-turn lane was found not to be warranted after 1 month, a second follow-up traf- fic study would be conducted 1 year after the opening of the surgery center for the same purpose. If either follow-up study determined that a left-turn lane was warranted, either the applicant would be obligated to construct the left-turn lane in conformance with FDOT standards, or FDOT would cash the bond and construct the left-turn lane. If the left-turn lane was found not to be warranted under either circumstance, FDOT would return the bond to the applicant. For purposes of the follow-up traffic studies, the left-turn lane would be warranted if both of the following criteria were met: • There were more than 10 actual left turns from SR 542 into the site during the typical weekday AM peak hour. • There were less than 60 5-sec eastbound vehicle gaps (time between vehicles approaching from the west) during the typical weekday AM peak hour at the site driveway. For pur- poses of the study, a 15-sec vehicle gap would be recorded as three 5-sec gaps. Figure 24. US 281/CR 800N intersection: post-improvement condition.

45 Figure 25 illustrates the post-development configuration of the facility’s access driveways on the south side of SR 542. Design Application #9: Installation of Left-Turn Lanes at Unsignalized Intersections in Conjunction with a Proposed Development (Note: The intersection location in this design application has been made anonymous at the request of the contributing agency. Street names have been changed.) Context Route 52 is a two-way north-south state highway. Within the area of the proposed development in the town of Har- rison, Route 52 has a posted speed of 35 mph and is classified as a minor rural arterial. The original cross section of Route 52 in Harrison accommodated three lanes—one lane north- bound and two lanes—and had an ADT of 18,000 vpd north of Meadow Terrace in the year 2008. Within Harrison, two local streets—Meadow Terrace and Parent Lane—intersect Route 52 as unsignalized T-intersections located within approximately 200 ft of each other. Meadow Terrace, the northerly roadway, intersects Route 52 from the west and provides access to approximately two dozen single- family homes and a few small commercial establishments before dead-ending approximately 1,600 ft west of Route 52. Parent Lane, the southerly roadway, intersects Route 52 from the east and serves as one of two access points to an elementary school, located approximately 1,400 ft east of Route 52. Both intersections are stop controlled on the side-street approaches to Route 52. This area of Harrison is primarily suburban with many single-family residences, as well as some supporting commercial uses primarily abutting Route 52. Design Request In 2004, the state received an application for the proposed development of an approximate 291,000-square-ft retail devel- opment on the west side of Route 52 in Harrison. The proposed development included a 133,000-square-ft home improvement store, a 63,000-square-ft supermarket with a 7,000-square-ft mezzanine, 74,000 square ft of retail space, and two free-standing restaurants totaling 14,000 square ft. Approximately 1,500 park- ing spaces would be provided as part of the development. The proposed development was projected to generate 1,962 vehicle trips during the weekday PM peak hour and 2,648 vehicle trips during the Saturday midday peak hour. Access to the development was proposed via two signalized access driveways connecting to the west side of Route 52. Both driveways were proposed to be aligned opposite existing local streets intersecting Route 52 from the east. The southerly access driveway was proposed to be located on the west side of Route 52, approximately 300 ft north of Meadow Terrace. Given the size of the proposed development relative to the available capacity of the street network in the surrounding area, a significant number of specific roadway improvements were proposed to accommodate the projected future travel demands associated with the development. These improve- ments included traffic signal installations at a number of stop- controlled intersections; roadway widening to accommodate exclusive right-turn, left-turn, and through lanes; realignment of existing roadways; widening of the off-ramps at a nearby interchange; installation of sidewalks; installation of guide signs; and other transportation-related improvements. Included in the package of improvements proposed by the applicant were provisions to widen Route 52 to accommodate back-to-back left-turn lanes at the unsignalized T-intersections of Meadow Terrace/Route 52 and Parent Lane/Route 52. Acquisition of right-of-way along Route 52 was not required to accommodate this improvement. Design Considerations and Analysis During the development review process, the applicant’s engineer proposed a widening of Route 52 along the site frontage (north of Meadow Terrace) to provide additional lanes. This widening provided an opportunity to introduce back-to-back left-turn lanes on Route 52 at the adjacent intersections of Parent Lane and Meadow Terrace. The state’s engineering staff felt that the left-turn lanes were necessary to remove left-turning motorists from the through travel (Source: Google Earth™ mapping service.) Figure 25. Subject development, located south of SR 542.

46 lanes, thereby improving capacity, operations, and safety in the vicinity of the development. As a result, the applicant included improvement plans for a northbound left-turn lane at the Meadow Terrace/Route 52 intersection, as well as a southbound left-turn lane at the Parent Lane/Route 52 intersection. The purpose of these left- turn lanes was to provide a safe refuge for left-turning vehicles waiting to turn across oncoming through traffic, and reduce the propensity for delays associated with northbound and south- bound through traffic waiting behind left-turning vehicles at these intersections. The lengths of both left-turn lanes were limited by the existing separation distance between Meadow Terrace and Parent Lane (approximately 200 ft). Design Result Figure 26 illustrates the final design at the Meadow Terrace/ Route 52 and Parent Place/Route 52 intersections. The design maintains two 11-ft travel lanes in the southbound direc- tion and one 11-ft travel lane in the northbound direction, and provides back-to-back 11-ft exclusive left-turn lanes. A transition taper of approximately 75 ft separates the left-turn lanes. Approximately 75 ft of vehicle storage is provided in the southbound left-turn lane at Parent Lane, which is sufficient to accommodate three passenger cars, or one tractor-trailer and one passenger car. Approximately 50 ft of vehicle storage is provided in the northbound left-turn lane at Meadow Ter- race, which is sufficient to accommodate two passenger cars or one tractor-trailer. In the northbound direction, the left- turn lane continues north of Meadow Terrace and becomes an exclusive left-turn lane at the adjacent signalized inter- section providing access to the proposed development. Design Application #10: Installation of an Exclusive Left-Turn Lane at an Unsignalized Suburban Intersection Between a State Highway and a Local Street Context SR 76 (also known as SW Kanner Highway) is a two-way state highway that extends between Lake Okeechobee and the city of Stuart in Florida. SR 76 is primarily an east-west highway for much of its length but generally follows a north- south alignment near the intersection with SW Tropical Ave- nue. SW Tropical Avenue is a two-way local street in Stuart that intersects the west side of SR 76, forming an unsignalized T-intersection. The intersection is stop controlled on the SW Tropical Avenue (eastbound) approach only. In the vicinity of SW Tropical Avenue, SR 76 is an undivided roadway clas- sified as an arterial. SR 76 also has a posted speed of 50 mph, and initially accommodated one 12-ft lane and a 6-ft paved shoulder in each direction. SW Tropical Avenue has a posted speed of 30 mph and accommodates one 11-ft lane in each direction and no shoulder. The SR 76/SW Tropical Avenue Figure 26. Final geometric layout of Meadow Terrace/Route 52 and Parent Lane/Route 52 intersections.

47 intersection is located in a primarily suburban area of Stu- art. Land uses adjacent to the intersection include residential housing (single-family homes and mobile homes) to the west of SR 76, and a nursery and golf course to the east. Figure 27 illustrates the original, pre-improvement configuration of the SR 76/Tropical Avenue intersection. Design Request In response to a citizen’s letter requesting that a separate left-turn lane be provided on SR 76 to accommodate turns onto SW Tropical Avenue, District 4 staff at FDOT conducted an engineering study of traffic operations and safety at the SR 76/SW Tropical Avenue intersection. As part of this study, pedestrian counts and vehicular turning-movement counts were conducted at the intersection during the typical weekday morning (7:00 to 10:00 AM), midday (11:00 AM to 1:00 PM), and afternoon (3:00 to 6:00 PM) peak hours. In addition, crash data spanning the 3-year period from 1997 through 1999 were reviewed. Design Considerations and Analysis The crash data revealed that of the nine crashes that occurred during the 3-year study period, a majority (56 percent) were rear-end crashes that were attributed to the lack of either a northbound left-turn lane on SR 76 or a southbound right- turn lane. The contributing causes included “improper pass- ing,” “careless driving,” and “failure to yield right-of-way.” Over the 3-year period, crashes at the intersection resulted in three injuries to vehicle occupants. Left-turn volumes from SR 76 onto SW Tropical Avenue were found to be 31 vehicles during the weekday morning peak hour, 18 vehicles during the weekday midday peak hour, and 42 vehicles during the weekday afternoon peak hours. Field observations revealed that motorists traveling at relatively high speeds on northbound SR 76 were forced to decelerate to a stop and wait for left-turning vehicles to turn, creating potential conflicts. Some northbound motorists on SR 76 were also observed using the shoulder to pass stopped left-turning vehicles on the right (east) side. These behaviors (Source: Florida Department of Transportation. Used by permission.) Figure 27. Pre-improvement condition diagram: SR 76/Tropical Avenue intersection.

48 resulted in damage to the east shoulder on SR 76 and cre- ated potential sideswipe conflicts with left-turning vehicles. A total of five pedestrians were observed during the course of the 8-hour count. Based on a review of the crash data and traffic volume data collected in the field, FDOT District 4 staff concluded that an exclusive northbound left-turn lane was needed at the SR 76/ SW Tropical Avenue intersection. The need for an exclusive southbound right-turn lane was also identified by FDOT Dis- trict 4 staff as part of their study. Deceleration Length (LD) As indicated in the 2010 FDOT Design Standards (31), FDOT uses a standard deceleration length based on the design speed (shown in Figure 28). The total deceleration dis- tance is 350 ft based on a design speed of 55 mph under rural conditions. This distance includes a standard 50-ft taper, as described in the subsequent section on taper length. Taper Length (LT) FDOT uses a taper length of 50 ft in all cases. This relatively short taper length increases the number of queued vehicles that can be stored in the turn lane (relative to a longer taper) and provides drivers with a distinct visual cue with respect to the transition from the through lane(s) to the left-turn lane. Queue Storage Length (LS) For the subject intersection, FDOT used 50 ft of storage (or the queue length equivalent of two passenger cars). Given the long deceleration distance at this location, sufficient queue storage is available if needed during times of peak traffic flow. Design Result Figure 29 illustrates the final design configuration of the SR 76/SW Tropical Avenue intersection with implementation of the northbound left-turn lane on SR 76. Design Example #11: Installation of Exclusive Left-Turn Lanes and a Traffic Signal at an Unsignalized Intersection Between a Local Street and a State Highway (Note: The intersection location in this design application has been made anonymous at the request of the contributing agency. Street names have been changed.) (Source: 2010 FDOT Design Standards, Index 301. Used by permission.) Figure 28. Deceleration distance values from 2010 FDOT Design Standards (31).

49 Context Conservatory Parkway is a two-way, east-west suburban arterial that serves as a border between two adjoining cities and is part of the state highway system as Route 90. The cross section of Route 90 is one 12-ft travel lane and a 10-ft shoulder in each direction. The posted speed limit on this section of Route 90 is 60 mph. Access points to Route 90 are minimal because there are few developed properties along this corridor. One of the few intersections on Route 90 is that of Spenlow Drive, a four-lane divided suburban collector that provides access to several properties in a mixed-use development, including a hospital, banks, and several medical and professional build- ings. The mixed-use development is bordered on either side by multiple residential subdivisions abutting Spenlow Drive. The intersection of Route 90 and Spenlow Drive was origi- nally built as a T-intersection, with southbound Spenlow Drive terminating at Route 90. As development increased, an exten- sion to Spenlow Drive was built on the south side of Route 90, resulting in a traditional 90-degree four-leg intersection (see Fig- ure 30). The approaches on Spenlow Drive were stop controlled. Design Request Engineers from the two cities and the state DOT monitored this intersection for several years as the adjacent development increased and traffic volumes increased correspondingly. The speed limit on Route 90 was originally 65 mph, but as a response to the increasing volumes, it was reduced to its current 60 mph approximately 1 year prior to the start of construction of the turning lanes. The engineers had origi- nally studied whether the intersection met one or more war- rants for a traffic signal; after the fourth leg of the intersection was built, more studies were conducted, and results indicated that the 8-hour, 4-hour, and peak-hour volume warrants were indeed met. However, the state DOT does not typically signalize a high-speed two-lane highway that does not have a left-turn lane. So the DOT agreed to allow the intersection to be signalized if left-turn lanes were added, and both cities began working toward signalizing the intersection and add- ing a left-turn bay. Prior to any projects being let, however, the DOT issued a statewide call for safety projects, and local officials submitted a left-turn lane project at this intersection. The project was selected for the safety funding, so only the cost of the traffic signal remained for the two cities to split. Design Considerations and Analysis The primary design considerations evaluated by the DOT were the high speeds on Route 90 and access to the nearby hospital. Right-of-way was available, and a nominally straight, level alignment at the intersection facilitated a straightforward design. The high speeds on Route 90 required longer tapers and deceleration lengths than for roads with lower speeds. The hospital access is located approximately 500 ft west of the intersection, which necessitated special accommodation, so the length of the widened roadway was extended west of Figure 29. SR 76/SW Tropical Avenue intersection: final condition. Tropical Avenue SR 76 (Source: Google Earth™ mapping service.) Figure 30. Route 90/Spenlow Drive intersection: condition before installation. Route 90 Spenlow Drive (Source: Google Earth™ mapping service.)

50 the hospital access to provide an eastbound turning lane for the hospital, upstream of the eastbound left-turn lane for the intersection. On the westbound approach to the intersection, the DOT used the typical lengths in their design manual. Spe- cifically, the DOT addressed the following items as part of the design: 1. Determine the deceleration length and taper length. The DOT’s roadway design manual provides a table of stan- dardized lengths for turn lanes on high-speed roadways. For roadways with a design speed of 65 mph, the table calls for a taper length of 150 ft and a deceleration length of 715 ft, which were provided on the westbound approach to the intersection and used as the baseline values for the eastbound approach. 2. Determine adjustments for hospital access. Because the hospital access is within about 500 ft of the intersection, the full deceleration length could not be provided in the eastbound left-turn lane at the intersection, so the length was shortened to about 475 ft. Upstream of the hospital access, a standard widening taper was applied to add the center lane, and a turning lane of approximately 400 ft was installed for the hospital access. This turning lane is striped as a TWLTL to distinguish it from the left-turn lane provided for the intersection. Design Result The intersection is completely within the city on the south side of Route 90, but the majority of the traffic travels into/out of the city on the north. For this reason, the northern city was willing to pay for half of the improvement costs. Additionally, as mentioned previously, the DOT successfully secured safety fund money to cover the cost of adding the left-turn lanes, so the resulting project was a group effort among the three agencies. The cities paid for the design, and all three agencies reviewed the plans. The DOT let the project with an Advanced Funding Agreement, with the northern city to pay 100 percent of the signal cost. The southern city had a separate contract with the northern city to reimburse it for 50 percent of the signal cost. Figure 31 illustrates the pavement markings in the final design configuration with implementation of the exclu- sive left-turn lanes on Route 90, with the additional provision for turns into the hospital to the west of the intersection. Figure 31. Pavement markings diagram for Route 90 at Spenlow Drive.