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Speed Reduction Techniques for Rural High-to-Low Speed Transitions (2011)

Chapter: CHAPTER FOUR High-To-Low Speed Transition Toolbox

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Suggested Citation:"CHAPTER FOUR High-To-Low Speed Transition Toolbox." National Academies of Sciences, Engineering, and Medicine. 2011. Speed Reduction Techniques for Rural High-to-Low Speed Transitions. Washington, DC: The National Academies Press. doi: 10.17226/22890.
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Suggested Citation:"CHAPTER FOUR High-To-Low Speed Transition Toolbox." National Academies of Sciences, Engineering, and Medicine. 2011. Speed Reduction Techniques for Rural High-to-Low Speed Transitions. Washington, DC: The National Academies Press. doi: 10.17226/22890.
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Suggested Citation:"CHAPTER FOUR High-To-Low Speed Transition Toolbox." National Academies of Sciences, Engineering, and Medicine. 2011. Speed Reduction Techniques for Rural High-to-Low Speed Transitions. Washington, DC: The National Academies Press. doi: 10.17226/22890.
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Suggested Citation:"CHAPTER FOUR High-To-Low Speed Transition Toolbox." National Academies of Sciences, Engineering, and Medicine. 2011. Speed Reduction Techniques for Rural High-to-Low Speed Transitions. Washington, DC: The National Academies Press. doi: 10.17226/22890.
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Suggested Citation:"CHAPTER FOUR High-To-Low Speed Transition Toolbox." National Academies of Sciences, Engineering, and Medicine. 2011. Speed Reduction Techniques for Rural High-to-Low Speed Transitions. Washington, DC: The National Academies Press. doi: 10.17226/22890.
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Suggested Citation:"CHAPTER FOUR High-To-Low Speed Transition Toolbox." National Academies of Sciences, Engineering, and Medicine. 2011. Speed Reduction Techniques for Rural High-to-Low Speed Transitions. Washington, DC: The National Academies Press. doi: 10.17226/22890.
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Suggested Citation:"CHAPTER FOUR High-To-Low Speed Transition Toolbox." National Academies of Sciences, Engineering, and Medicine. 2011. Speed Reduction Techniques for Rural High-to-Low Speed Transitions. Washington, DC: The National Academies Press. doi: 10.17226/22890.
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Suggested Citation:"CHAPTER FOUR High-To-Low Speed Transition Toolbox." National Academies of Sciences, Engineering, and Medicine. 2011. Speed Reduction Techniques for Rural High-to-Low Speed Transitions. Washington, DC: The National Academies Press. doi: 10.17226/22890.
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Suggested Citation:"CHAPTER FOUR High-To-Low Speed Transition Toolbox." National Academies of Sciences, Engineering, and Medicine. 2011. Speed Reduction Techniques for Rural High-to-Low Speed Transitions. Washington, DC: The National Academies Press. doi: 10.17226/22890.
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Suggested Citation:"CHAPTER FOUR High-To-Low Speed Transition Toolbox." National Academies of Sciences, Engineering, and Medicine. 2011. Speed Reduction Techniques for Rural High-to-Low Speed Transitions. Washington, DC: The National Academies Press. doi: 10.17226/22890.
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Suggested Citation:"CHAPTER FOUR High-To-Low Speed Transition Toolbox." National Academies of Sciences, Engineering, and Medicine. 2011. Speed Reduction Techniques for Rural High-to-Low Speed Transitions. Washington, DC: The National Academies Press. doi: 10.17226/22890.
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Suggested Citation:"CHAPTER FOUR High-To-Low Speed Transition Toolbox." National Academies of Sciences, Engineering, and Medicine. 2011. Speed Reduction Techniques for Rural High-to-Low Speed Transitions. Washington, DC: The National Academies Press. doi: 10.17226/22890.
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Suggested Citation:"CHAPTER FOUR High-To-Low Speed Transition Toolbox." National Academies of Sciences, Engineering, and Medicine. 2011. Speed Reduction Techniques for Rural High-to-Low Speed Transitions. Washington, DC: The National Academies Press. doi: 10.17226/22890.
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Suggested Citation:"CHAPTER FOUR High-To-Low Speed Transition Toolbox." National Academies of Sciences, Engineering, and Medicine. 2011. Speed Reduction Techniques for Rural High-to-Low Speed Transitions. Washington, DC: The National Academies Press. doi: 10.17226/22890.
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Suggested Citation:"CHAPTER FOUR High-To-Low Speed Transition Toolbox." National Academies of Sciences, Engineering, and Medicine. 2011. Speed Reduction Techniques for Rural High-to-Low Speed Transitions. Washington, DC: The National Academies Press. doi: 10.17226/22890.
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Suggested Citation:"CHAPTER FOUR High-To-Low Speed Transition Toolbox." National Academies of Sciences, Engineering, and Medicine. 2011. Speed Reduction Techniques for Rural High-to-Low Speed Transitions. Washington, DC: The National Academies Press. doi: 10.17226/22890.
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56 CHAPTER FOUR HIGH-TO-LOW SPEED TRANSITION TOOLBOX • The relative cost of implementation (i.e., high, moder- ate, low) • Possible impacts and cautions concerning the measure • Basic literature references. It is noted that in most cases where measures are imple- mented in the transition zone (as opposed to throughout a rural area or at the start of the urban area), road authorities tended to use multiple measures rather than relying on one measure (e.g., dragon’s teeth, a median island, and roadside signs to create a gateway feature). An array of engineering and infrastructure measures are available to practitioners for implementation in rural high- to-low speed transitions. This section of the synthesis identi- fies all of the measures that have been found in the conduct of this study and are in service. Each measure is described as follows: • Which jurisdictions are known to use this measure • Whether the measure is experimental, tested, or proven effective in transitioning speeds (and if proven, results will be provided) TREATMENT Central Islands/Raised Medians CATEGORY Geometric design COST High for physical medians Low for painted medians DESCRIPTION Narrow islands that are located either mid-block or at intersections and are placed between travel lanes. Median islands can be used to create a shift/deflection in the travel path of vehicles, or they may simply be used to narrow the “optical width” of the roadway by dividing the traveled way. Source: Berger and Linauer (1998) Continued on page 57

57 EFFECTIVENESS Medians have been shown to be very effective in lowering operating speeds, particularly when they create a deflection in the vehicle path. Berger and Linauer (1998) developed the following speed prediction models: Metric: V85 = 14.797Ln(L/2d)+19.779 Vm = 12.907Ln(L/2d)+17.753 Where: V85 = 85th percentile speed (km/h) Vm = mean speed (km/h) L = length of island + length of both tapers (m) d = lateral deflection of lane (m) U.S. Customary: V85 = 9.194Ln(L/2d)+12.290 Vm = 8.020Ln(L/2d)+11.031 Where: V85 = 85th percentile speed (mph) Vm = mean speed (mph) L = length of island + length of both tapers (ft) d = lateral deflection of lane (ft) Charlton and Baas (2006), in an assessment of the effects of speed management measures, determined that median islands reduce speeds by about 9%. Hallmark et al. (2007) studied the effects of a painted median in the transition zone and found no significant reduction in operating speed. However, a median created with tubular markers yielded up to a 5 km/h reduction in operating speed. In simulator studies, Dixon et al. (2008) found up to a 15.5 km/h reduction in the 85th percentile speed. JURISDICTIONS WHERE USED Iowa, Hamilton (Ontario), United Kingdom, Austria, New Zealand, Denmark, Germany POTENTIAL IMPACTS If the median island is used to create a lateral deflection, then attention needs to be given to the severity of the deflection to achieve speed reduction without compromising the motorist’s ability to navigate the transition. The raised island is a fixed obstacle that may increase the potential for single motor vehicle crashes. REFERENCES Berger W.J. and M. Linauer, “Raised Traffic Islands at City Limits—Their Effect on Speed,” Proceedings of 1998 Meeting of the International Cooperation on Theories and Concepts in Traffic Safety, Budapest, 1998. Dixon, K., H. Zhu, J. Ogle, J. Brooks, C. Hein, P. Aklluir, and M. Crisler, Determining Effective Roadway Design Treatments for Transitioning from Rural Areas to Urban Areas on State Highways, Final Report , FHWA Report No. FHWA-OR-RD-09-02, Federal Highway Administration, Washington, D.C., Sep. 2008. Hallmark, S.L., E. Peterson, E. Fitzsimmons, N. Hawkins, J. Resler, and T. Welch, Evaluation of Gateway and Low-Cost Traffic-Calming Treatments for Major Routes in Small, Rural Communities, Final Report No. CTRE Project 06-185, IHRB Project TR-523, Center for Transportation Research and Education, Iowa State University, Ames, Nov. 2007. Continued from page 56

58 TREATMENT Roundabout CATEGORY Geometric design COST High DESCRIPTION A one-way circular intersection that is characterized by a splitter island on all approaches and entering motorists yielding the right-of-way to motorists already on the circular roadway. EFFECTIVENESS Rodegerdts et al. (2007) developed speed prediction models for roundabout entries and exits as follows: Metric: Where: Vexit = the predicted exit speed for the roundabout (km/h) R1 = path radius on entry to the roundabout (m) R2 = path radius on the circulating roadway (m) R3 = path radius on exit from the roundabout (m) a, b = see Table 13 d3 = distance between the midpoint of the path on the circulating roadway and the point of interest on the exit (m) Venter = the predicted entry speed for the roundabout (km/h) d1 = distance between the point of interest on the entry and the midpoint of the path on the circulating roadway (m) Continued on page 59

59 U.S. CUSTOMARY: Where: Vexit = the predicted exit speed for the roundabout (mph) R1 = path radius on entry to the roundabout (ft) R2 = path radius on the circulating roadway (ft) R3 = path radius on exit from the roundabout (ft) a, b = see Table 13 d3 = distance between the midpoint of the path on the circulating roadway and the point of interest on the exit (ft) Venter = the predicted entry speed for the roundabout (mph) d1 = distance between the point of interest on the entry and the midpoint of the path on the circulating roadway (ft) Table 13: Speed Prediction Parameters for Roundabouts Metric US Customary e = +0.02 e = -0.02 e = +0.02 e = -0.02 a 8.7602 8.6164 3.4415 3.4614 b 0.3861 0.3673 0.3861 0.3673 d2 = distance between the point of interest on the entry and the midpoint of the path on the circulating roadway (m) The predicted speeds are independent of the approach speeds and are determined by the geometry of the circulating roadway. JURISDICTIONS WHERE USED United States, Canada, Europe, Australia POTENTIAL IMPACTS Roundabouts with higher design speeds for the circulating roadway may require more property for construction. REFERENCES Rodegerdts, L., M. Blogg, E. Wemple, E. Myers, M. Kyte, M. Dixon, G. List, A. Flannery, R. Troutbeck, W. Brilon, N. Wu, B. Persaud, C. Lyon, D. Harkey, and D. Carter, NCHRP Report 572: Roundabouts in the United States, Transportation Research Board of the National Academies, Washington, D.C., 2007. Continued from page 58

60 TREATMENT Road or Lane Narrowings CATEGORY Geometric design COST High DESCRIPTION Any form of narrowing the road platform, including lane narrowing from the road edges or through the introduction of a raised or painted median. EFFECTIVENESS Charlton and Baas (2006) report an 11% to 20% reduction in operating speed as a result of visually narrowing the road in transition zones JURISDICTIONS WHERE USED United Kingdom, Denmark, Netherlands, Ireland, New Zealand POTENTIAL IMPACTS Narrowings must take into account the number and classification of vehicles using the facility. Frequent use by large commercial vehicles or agricultural equipment may require wider pavements than otherwise. REFERENCES Charlton, S.S. and P.H. Baas, Speed Change Management for New Zealand Roads, Land Transport New Zealand Research, Report 300, Wellington, New Zealand, 2006, 144 pp.

61 TREATMENT Road Diets CATEGORY Geometric design/traffic control COST Medium to High DESCRIPTION A reduction in the number of travel lanes for motorized traffic, with the excess road space generally reallocated to bicycle lanes, painted medians, or center turn lanes. Source: http://www.tfhrc.gov/safety/hsis/pubs/04082/index.htm EFFECTIVENESS Knapp and Rosales (2007) reviewed a number of studies on road diets and found speed reductions of 5 mph (8 km/h) or less, but up to a 70% reduction in excessive speeding. Crash reductions are generally expected, with 20 to 40% reductions experienced. JURISDICTIONS WHERE USED United States, Canada POTENTIAL IMPACTS The road diet may reduce the capacity of a facility depending on the number and types of turns, the presence of heavy vehicles, and the number and frequency of transit stops. REFERENCES Knapp, K.K. and J.A. Rosales, “Four-Lane to Three-Lane Conversions: An Update and a Case Study,” Proceedings of the 3rd Urban Street Symposium, Seattle, Washington, June 2007, http://www.urbanstreet.info/3rd_symp_proceedings/Four- Lane%20to%20Three-Lane.pdf, accessed on August 31, 2009.

62 TREATMENT Chicanes or Horizontal Deflections CATEGORY Geometric design COST Medium to High DESCRIPTION Introducing horizontal deflections and shifts in the alignment of the road that require motorists to slow down as they negotiate the road. Source: San Francisco Municipal Transportation Agency (www.sfmta.com/cms/ocalm/13567.html) EFFECTIVENESS Chicanes or horizontal deflections have not been tried in transition zones as an isolated measure; they are typically installed in conjunction with other devices. The effects of horizontal deflections on speed are directly proportional to the severity of the deflection, with greater deflections generally producing greater speed reductions. However, Lamberti et al. (2009) tested a gateway treatment with and without a horizontal deflection and found speed reductions of the same magnitude for both. This indicates that the gateway signing and pavement markings may be sufficient to slow traffic without having to introduce horizontal deflection elements. JURISDICTIONS WHERE USED United Kingdom, Italy POTENTIAL IMPACTS The chicane or horizontal deflection is a physical obstruction in the traveled way, so approaching motorists need clear visibility and adequate warning of the chicane so as to safety traverse it. Chicanes may increase the incidence of single vehicle collisions. REFERENCES Lamberti, R., D. Abate, M.L. De Guglielmo, G. Dell’Acqua, T. Esposito, F. Galante, F. Mauriello, A. Montella, and M. Pernetti, “Perceptual Measures and Physical Devices for Traffic Calming Along a Rural Highway Crossing a Small Urban Community: Speed Behavior Evaluation in a Driving Simulator,” TRB Annual Meeting CD-ROM, Transportation Research Board, Washington, D.C., 2009.

63 TREATMENT Countdown Speed Signs/Markers CATEGORY Traffic control devices COST Low A longitudinal series of three traditional speed limit signs that are complemented with rectangular signs mounted below the speed limit signs. The complementary sign is a white background with one, two, or three diagonal slashes. The sign furthest upstream has the three diagonal slashes, followed by the sign with two slashes and then the sign with one slash, forming a non-numeric countdown. Direction of travel → (NOTE: European style speed limit sign shown) EFFECTIVENESS Barker and Helliar-Symons (1997) found no significant effect on mean speeds when countdown markers were used on the approaches to villages. JURISDICTIONS WHERE USED United Kingdom POTENTIAL IMPACTS The countdown intended to be conveyed to the motorist by this signing method is done so using non-numeric, coded information. Therefore, public education and repeated exposure to the sign would be necessary for this sign to deliver any significant results. REFERENCES Barker, J. and R.D. Helliar-Symons, “Countdown Signs and Roundel Markings Trails,” TRL Report 201, Transport Research Laboratory, Crowthorne, U.K., 1997.

64 TREATMENT Speed Feedback Signs CATEGORY Traffic control devices COST Medium DESCRIPTION Electronic signs placed at the roadside are connected to a device that measures the speed of approaching vehicles and displays the actual travel speed to motorists. Source: Richard Drdul EFFECTIVENESS Donnell and Cruzado (2008) used speed feedback signs in transition zones, which showed mean speed reductions of approximately 6 mph (10 km/h) at the speed feedback sign and downstream of the sign. This effect was present only while the signs were in place, and mean speeds rebounded to before levels in the week after sign removal. JURISDICTIONS WHERE USED Texas, Pennsylvania, United Kingdom POTENTIAL IMPACTS The cost of installation could be much higher than expected if a source of electricity is not readily available at the sign placement. Solar power is an option, but the solar panels are subject to theft. REFERENCES Donnell, E.T. and I. Cruzado, Effectiveness of Speed Minders in Reducing Driving Speeds on Rural Highways in Pennsylvania, Final Report, The Thomas D. Larson Pennsylvania Transportation Institute, Pennsylvania State University, June 2008.

65 TREATMENT Speed-Activated Speed Limit Signs CATEGORY Traffic control devices COST Medium DESCRIPTION Electronic signs placed at the roadside that are connected to a device that measures the speed of approaching vehicles. Should the measured speed exceed the legal speed limit, then the electronic sign is activated to display the legal speed limit. The speed limit may be accompanied by a “SLOW DOWN” message. Source: Winnett and Wheeler (2002) EFFECTIVENESS Winnett and Wheeler (2002) produced up to an 80% change in the percentage of vehicles exceeding the speed limit using vehicle-activated speed signs on the approaches to villages. JURISDICTIONS WHERE USED Iowa, Washington (Tacoma, Redmond), Maryland (Anne Arundel County), Canada (Ontario, Alberta, and British Columbia), United Kingdom POTENTIAL IMPACTS The cost of installation could be much higher than expected if a source of electricity is not readily available at the sign placement. Solar power is an option, but the solar panels are subject to theft. REFERENCES Winnett, M.A. and A.H. Wheeler, “Vehicle-Activated Signs; A Large Scale Evaluation,” TRL Report 549, Transport Research Laboratory, Crowthorne, U.K., 2002.

66 TREATMENT Transitional Speed Limits (or Stepped-Down Speed Limit) CATEGORY Traffic control devices COST Low DESCRIPTION Provision of an intermediate or stepped-down speed limit to ease the transition from a high-to-low speed area. For example, a short section of 40 mph speed zone inserted between a 55 mph rural speed zone and a 30 mph urban speed zone. EFFECTIVENESS Hildebrand et al. (2004) tested stepped-down speed limits at seven high-to-low speed transitions that were 25 mph (40 km/h) or more, and found that inserting a transitional speed limit had no significant effect on mean speed, speed dispersion, or the percentage of motorists exceeding the speed limit. JURISDICTIONS WHERE USED United States, Canada, United Kingdom, Australia, Europe POTENTIAL IMPACTS None identified. REFERENCES Hildebrand, E.D., A. Ross, and K. Robichaud, “The Effectiveness of Transitional Speed Zones,” ITE Journal, Vol. 74, No. 10, Institute of Transportation Engineers, Washington, D.C., 2004, pp. 30–38.

67 TREATMENT Removal of Pavement Markings CATEGORY Traffic control devices COST Medium DESCRIPTION Removing the directional dividing line and/or the edge lines from the pavement surface to create discomfort for motorists, causing them to slow down commensurately. Source: Kennedy (2005) EFFECTIVENESS Removal of the directional dividing lines in two cases in the United Kingdom resulted in as much as a 7 mph (11 km/h) reduction in speed (Quimby and Castle 2006). JURISDICTIONS WHERE USED United Kingdom POTENTIAL IMPACTS This measure has been used in villages, and may not be suitable for transition zones. Longitudinal pavement markings play an important role in lane keeping and reducing crashes that result from lane departures (head-on collisions, sideswipe collisions, or run-off-road collisions). This measure is not suitable for areas where the forward visibility of the road ahead is restricted and motorists rely on the longitudinal markings to maintain lateral position. REFERENCES Quimby, A. and J. Castle, A Review of Simplified Streetscape Schemes, Project Report PPR292, TRL Limited, Crowthorne, U.K., Jan. 2006.

68 TREATMENT Optical Speed Bars CATEGORY Traffic control devices COST Low DESCRIPTION Transverse markings placed in and across the travel lane with the intent of increasing the optical flow of information and creating a sense of increasing speed. The speed bars may be evenly spaced or exponentially spaced with a decreased spacing as one travels downstream. Source: Arnold and Lantz (2008) EFFECTIVENESS Arnold and Lantz (2008) tested optical speed bars on the approach to a rural village and found a 3 to 9.5 mph (5 to 15 km/h) reduction in speed. It is unknown whether this effect can be sustained over time. Fitch and Crum (2007) found only a 1.0 mph (1.6 km/h) reduction in the 85th percentile speed when testing optical speed bars at four towns in Vermont. JURISDICTIONS WHERE USED Virginia, Vermont POTENTIAL IMPACTS Transverse pavement markings increase maintenance costs if they are placed in the wheel paths of vehicles. Also, pavement markings are not visible from significant distances upstream, so placement requires careful consideration. REFERENCES Arnold, E.D. and K.E. Lantz, Evaluation of Best Practices in Traffic Operations and Safety: Phase I: Flashing LED Stop Sign and Optical Speed Bars, Final Report, Virginia Transportation Research Council, Charlottesville, June 2007. Fitch, J. and N. Crum, Dynamic Striping in Four Towns Along Vermont Route 30—Final Report, Report No. 2007-14, Vermont Agency of Transportation, Montpelier, Oct. 2007.

69 TREATMENT Speed Humps, Raised Crosswalks, Raised Intersections, and Vertical Deflections CATEGORY Surface treatment COST Medium to High DESCRIPTION A relatively abrupt change in the elevation of the road surface so as to create an uncomfortable feeling for motorized traffic when the feature is traversed at a high speed. Source: Richard Drdul EFFECTIVENESS Vertical deflections at high-to-low speed transitions have not been used extensively in practice because the profession is wary of the potential for vehicle damage and lost control crashes resulting from a motorist striking the deflection at full speed. Nonetheless, Charlton and Baas (2006) report speed cushions and speed humps in transition zones could reduce speeds by 9% and 21%, respectively. JURISDICTIONS WHERE USED United Kingdom POTENTIAL IMPACTS Vertical measures are particularly troubling if motorists are not provided with sufficient warning of the deflection. Traversing these features at high operating speeds may cause vehicle damage and cause a motorist to lose control of the vehicle. REFERENCES Charlton, S.S. and P.H. Baas, Speed Change Management for New Zealand Roads, Report 300, Land Transport New Zealand Research, Wellington, 2006, 144 pp.

70 TREATMENT Rumblewave Surfaces CATEGORY Pavement surface treatment COST Medium to high DESCRIPTION An undulating road surface that resembles a series of closely spaced speed humps using a sinusoidal profile. The amplitude of the waves are about one quarter of an inch, and the wavelength is in the order of 1.1 feet. Source: Department for Transport (2005) EFFECTIVENESS At seven pilot locations, rumblewave surfaces produced reductions in both the mean and 85th percentile speeds from 1% to 6% (Department for Transport, 2005). JURISDICTIONS WHERE USED United Kingdom POTENTIAL IMPACTS Rumblewave surfaces are experimental. They may cause some maintenance concerns, particularly where snow and ice build-up may cause winter weather hazards. REFERENCES Department for Transport, Rumblewave Surfacing, Traffic Advisory Leaflet 1/05, Department for Transport, London, United Kingdom, Jan. 2005, 6 pp.

71 TREATMENT Gateway CATEGORY Roadside features COST Low to High DESCRIPTION Measures and elements that are placed at the urban/rural threshold and collectively present a visual cue to the driver that this is the point of change in roadway character. Gateways can consist of a simple sign at the roadside, a raised island, or an elaborate collection of measures including freestanding structures placed over/across the traveled way, colored pavement, and pavement markings. Source: Veneziano et al. (2009) Source: Andersson et al. (2008) EFFECTIVENESS Andersson et al. (2008) analyzed the safety performance of 251 town gates across Denmark and found that overall town gates increased the number of property damage only collisions by 34% and did not have any significant effect on personal injury crashes. If the gates are broken down by those with physical measures, those with visual measures, and those with combined physical and visual measures—the combined measures gates performed the best, yielding a 28% decrease in injury collisions and a 36% increase in property damage collisions. Also, the researchers found that gates in transition zones where the difference in the posted speed limit is less than 20 mph (30 km/h) perform better than gates in zones with speed differences of 20 mph (30 km/h) or more. Veneziano et al. (2009) reviewed seven gateways constructed in California that consisted solely of freestanding structures and roadside signs, and found that they are not detrimental to safety. JURISDICTIONS WHERE USED California, United Kingdom, Denmark POTENTIAL IMPACTS Gateways become fixed objects at the roadside and may increase the severity of run-off-road crashes. Gateways need to be conspicuous to be effective, but should blend in with the surrounding environment (particularly in historic areas). Gateways should be visible over at least the stopping sight distance to avoid surprising the driver. REFERENCES Veneziano, D., Z. Ye, J. Fletcher, J. Ebeling, and F. Shockley, Evaluation of the Gateway Monument Demonstration Program: Safety, Economic and Social Impact Analysis, Western Transportation Institute, College of Engineering, Montana State University, Sep. 2009, 141 pp. Andersson, P.K., B. la Cour Lund, P.V. Greibe, and L. Herrstedt, Byporte: de trafiksikkerhedsmaessige efffeckter, Trafitec Scion-DTU, July 2008, 116 pp [Online]. Available: http://www.trafitec.dk/pub/byporte%20notat.pdf [accessed Sep. 3, 2009].

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TRB’s National Cooperative Highway Research Program (NCHRP) Synthesis 412: Speed Reduction Techniques for Rural High-to-Low Speed Transitions explores techniques for lowering traffic speeds in rural transition zones. Transition zones are those portions of high-speed roads that have lower posted speed limits as the roadway approaches a settlement.

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