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Not only did I read it, I did a text search to make sure I got all the
references to 85th percentile speed. Instead of telling me I did my homework poorly (which is not true), why not enligthen me. You are back to acting like a fifth grader again - you know - the na-na-na-na, I know something you don't know game you seem to like to play. If I am missing something elighten me. If you know somthing I don't know, just claiming you know it without sharing the information is just wrong. No one learns anything, and I am left with the suspicion you are making stuff up. References to the 85th percentile speed from the 2003 Edition of the MUTCD (see http://www.okladot.state.ok.us/traff...03/pdfVersion/ ): Chapter 1 - Section 1A.13 Definitions of Words and Phrases in This Manual "..... 79. Speed-speed is defined based on the following classifications: (a) Advisory Speed-a recommended speed for all vehicles operating on a section of highway and based on the highway design, operating characteristics, and conditions. (b) Average Speed-the summation of the instantaneous or spot-measured speeds at a specific location of vehicles divided by the number of vehicles observed. (c) Design Speed-a selected speed used to determine the various geometric design features of a roadway. (d) 85th-Percentile Speed-The speed at or below which 85 percent of the motor vehicles travel. (e) Operating Speed-a speed at which a typical vehicle or the overall traffic operates. Operating speed might be defined with speed values such as the average, pace, or 85th-percentile speeds. (f) Pace Speed-the highest speed within a specific range of speeds that represents more vehicles than in any other like range of speed. The range of speeds typically used is 10 km/h or 10 mph. (g) Posted Speed-the speed limit determined by law and shown on Speed Limit signs. (h) Statutory Speed-a speed limit established by legislative action that typically is applicable for highways with specified design, functional, jurisdictional and/or location characteristic and is not necessarily shown on Speed Limit signs. ......" Chapter 2 - Section 2A.16 Standardization of Location "Standard: ".....Signs requiring different decisions by the road user shall be spaced sufficiently far apart for the required decisions to be made reasonably safely. One of the factors considered when determining the appropriate spacing shall be the posted or 85th-percentile speed......" Section 2B.07 Multiway Stop Applications ".....Guidance: The decision to install multiway stop control should be based on an engineering study. The following criteria should be considered in the engineering study for a multiway STOP sign installation: A. Where traffic control signals are justified, the multiway stop is an interim measure that can be installed quickly to control traffic while arrangements are being made for the installation of the traffic control signal. B. A crash problem, as indicated by 5 or more reported crashes in a 12-month period that are susceptible to correction by a multiway stop installation. Such crashes include right- and left-turn collisions as well as right-angle collisions. C. Minimum volumes: 1. The vehicular volume entering the intersection from the major street approaches (total of both approaches) averages at least 300 vehicles per hour for any 8 hours of an average day, and 2. The combined vehicular, pedestrian, and bicycle volume entering the intersection from the minor street approaches (total of both approaches) averages at least 200 units per hour for the same 8 hours, with an average delay to minor-street vehicular traffic of at least 30 seconds per vehicle during the highest hour, but 3. If the 85th-percentile approach speed of the major-street traffic exceeds 65 km/h or exceeds 40 mph, the minimum vehicular volume warrants are 70 percent of the above values......" Section 2B.09 YIELD Sign Applications ".....Option: YIELD signs may be used instead of STOP signs if engineering judgment indicates that one or more of the following conditions exist: A. When the ability to see all potentially conflicting traffic is sufficient to allow a road user traveling at the posted speed, the 85th-percentile speed, or the statutory speed to pass through the intersection or to stop in a reasonably safe manner...." Section 2B.13 Speed Limit Sign (R2-1) "Standard: After an engineering study has been made in accordance with established traffic engineering practices, the Speed Limit (R2-1) sign (see Figure 2B-1) shall display the limit established by law, ordinance, regulation, or as adopted by the authorized agency. The speed limits shown shall be in multiples of 10 km/h or 5 mph. Guidance: At least once every 5 years, States and local agencies should reevaluate non-statutory speed limits on segments of their roadways that have undergone a significant change in roadway characteristics or surrounding land use since the last review. No more than three speed limits should be displayed on any one Speed Limit sign or assembly. When a speed limit is to be posted, it should be within 10 km/h or 5 mph of the 85th-percentile speed of free-flowing traffic. Option: Other factors that may be considered when establishing speed limits are the following: A. Road characteristics, shoulder condition, grade, alignment, and sight distance; B. The pace speed; C. Roadside development and environment; D. Parking practices and pedestrian activity; and E. Reported crash experience for at least a 12-month period. Two types of Speed Limit signs may be used: one to designate passenger car speeds, including any nighttime information or minimum speed limit that might apply; and the other to show any special speed limits for trucks and other vehicles. A changeable message sign that changes the speed limit for traffic and ambient conditions may be installed provided that the appropriate speed limit is shown at the proper times. A changeable message sign that displays to approaching drivers the speed at which they are traveling may be installed in conjunction with a Speed Limit sign. Guidance: If a changeable message sign displaying approach speeds is installed, the legend YOUR SPEED XX km/h (MPH) or such similar legend should be shown. The color of the changeable message legend should be a yellow legend on a black background or the reverse of these colors. Support: Advisory Speed signs are discussed in Sections 2C.36 and 2C.46 and Temporary Traffic Control Zone Speed signs are discussed in Part 6." Table 2C-4. Guidelines for Advance Placement of Warning Signs You'll have to go to the document to see the reference.It is a table showing distances for posting speed change signs. Section 2C.36 Advisory Exit, Ramp, and Curve Speed Signs (W13-2, W13-3, W13-5) ".....and Advisory Speed sign combination, or when there is a need to remind road users of the recommended speed, or where the recommended speed changes because of a change in curvature (see Section 2C.06). Based on engineering judgment, the Curve Speed sign may be installed on the inside or outside of the curve to enhance its visibility. The advisory speed may be the 85th-percentile speed of free-flowing traffic, the speed corresponding to a 16-degree ball bank indicator reading, or the speed otherwise determined by an engineering study because of unusual circumstances. Support: A 10-degree ball-bank indicator reading, formerly used in determining advisory speeds, is based on research from the 1930s. In modern vehicles, the 85th-percentile speed on curves approximates a 16-degree reading. This is the speed at which most drivers' judgment recognizes incipient instability along a ramp or curve....." Section 2C.46 Advisory Speed Plaque (W13-1) ".....Because changes in conditions, such as roadway geometrics, surface characteristics, or sight distance, might affect the advisory speed, each location should be periodically evaluated and the Advisory Speed plaque changed if necessary. Option: The advisory speed may be the 85th-percentile speed of free-flowing traffic, the speed corresponding to a 16-degree ball bank indicator reading, or the speed otherwise determined by an engineering study because of unusual circumstances. Support: A 10-degree ball-bank indicator reading, formerly used in determining advisory speeds, is based on research from the 1930s. In modern vehicles, the 85th-percentile speed on curves approximates a 16-degree reading.This is the speed at which most drivers' judgment recognizes incipient instability along a ramp or curve....." Section 2E.21 Changeable Message Signs ".....To the extent practical, the design and application of changeable message signs should conform to the general principles of this Manual. Within the context of Section 2A.07, these practices should be followed for mainline freeway and expressway applications: A. Changeable message signs should be capital letters and have a desirable letter size of 450 mm (18 in) or a minimum letter size of 265 mm (10.6 in). Signs should be limited to not more than 3 lines with not more than 20 characters per line. B. No more than two displays should be used within any message cycle. C. Each display should convey a single thought. D. The entire message cycle should be readable at least twice by drivers traveling at the posted speed, the off-peak 85th-percentile speed, or the operating speed....." Chapter 3 - Section 3B.01 Yellow Centerline Pavement Markings and Warrants ".....For three-lane roadways having a posted or statutory speed limit of 70 km/h (45 mph) or greater, the lane transition taper length should be computed by the formula L = 0.62 WS for speeds in km/h (L = WS for speeds in mph). For roadways where the posted or statutory speed limit is less than 70 km/h (45 mph), the formula L = WS2/155 for speeds in km/h (L = WS2/60 for speeds in mph) should be used to compute taper length. Under both formulas, L equals the taper length in meters (feet), W equals the width of the center lane or offset distance in meters (feet), and S equals the 85th-percentile speed or the posted or statutory speed limit, whichever is higher. Standard: The minimum lane transition taper length shall be 30 m (100 ft) in urban areas and 60 m (200 ft) in rural areas. On roadways with centerline markings, no-passing zone markings shall be used at horizontal or vertical curves where the passing sight distance is less than the minimum necessary for reasonably safe passing at the 85th-percentile speed or the posted or statutory speed limit as shown in Table 3B-1. The passing sight distance on a vertical curve is the distance at which an object 1.07 m (3.5 ft) above the pavement surface can be seen from a point 1.07 m (3.5 ft) above the pavement (see Figure 3B-5). Similarly, the passing sight distance on a horizontal curve is the distance measured along the centerline (or right-hand lane line of a three-lane roadway) between two points 1.07 m (3.5 ft) above the pavement on a line tangent to the embankment or other obstruction that cuts off the view on the inside of the curve (see Figure 3B-5)....." Table 3B-1. Minimum Passing Sight Distances Another table you'll have to pull up for yourself. Figure 3B-5. Method of Locating and Determining the Limits of No-Passing Zones at Curves A figure you'll ahve to go see. Section 3B.09 Lane Reduction Transition Markings ".....For roadways having a posted or statutory speed limit of 70 km/h (45 mph) or greater, the transition taper length for a lane reduction should be computed by the formula L = 0.62 WS for speeds in km/h (L = WS for speeds in mph). For roadways where the posted or statutory speed limit is less than 70 km/h (45 mph), the formula L = WS2/155 for speeds in km/h (L = WS2/60 for speeds in mph) should be used to compute taper length. Under both formulas, L equals the taper length in meters (feet), W equals the width of the offset distance in meters (feet), and S equals the 85th-percentile speed or the posted or statutory speed limit, whichever is higher......" Figure 3B-12. Examples of Lane Reduction Markings Another figure. Chapter 4 - Section 4C.01 Studies and Factors for Justifying Traffic Control Signals ".....E. The posted or statutory speed limit or the 85th-percentile speed on the uncontrolled approaches to the location..... ".....C. The posted or statutory speed limit or the 85th-percentile speed on controlled approaches at a point near to the intersection but unaffected by the control....." Section 4C.02 Warrant 1, Eight-Hour Vehicular Volume ".....If the posted or statutory speed limit or the 85th-percentile speed on the major street exceeds 70 km/h or exceeds 40 mph, or if the intersection lies within the built-up area of an isolated community having a population of less than 10,000, the traffic volumes in the 70 percent columns in Table 4C-1 may be used in place of the 100 percent columns......" ".....Option: If the posted or statutory speed limit or the 85th-percentile speed on the major street exceeds 70 km/h or exceeds 40 mph, or if the intersection lies within the built-up area of an isolated community having a population of less than 10,000, the traffic volumes in the 56 percent columns in Table 4C-1 may be used in place of the 80 percent columns....." Section 4C.03 Warrant 2, Four-Hour Vehicular Volume Additional references similar to the above for Section 4C.02 Section 4C.08 Warrant 7, Crash Experience Additional references similar to the above for Section 4C.02 Section 4D.14 Coordination of Traffic Control Signals ".....Option: Different sizes of signal lenses may be used in the same signal face or signal head, except for the prohibitions listed in the Standards in this Section. Guidance: Three-hundred millimeter (12 in) signal lenses should be used for all signal indications for the following: A. Approaches with 85th-percentile approach speeds exceeding 60 km/h (40 mph); B. Approaches where a traffic control signal might be unexpected; C. All approaches without curbs and gutters where only post-mounted signal heads are used; and D. Locations where there is a significant percentage of elderly drivers....." Table 4D-1. Minimum Sight Distance A table you'll have to go to the document to see. Section 4F.01 Applications of Emergency-Vehicle Traffic Control Signals ".....The sight distance determination should be based on the location of the visibility obstruction for the critical approach lane for each street or drive and the posted or statutory speed limit or 85th-percentile speed on the major street, whichever is higher....." Chapter 5 - Section 5A.03 Design ".....The typical sizes for signs installed on low-volume roads shall be as shown in Table 5A-1. The Minimum sign sizes shall only be used on low-volume roads where the 85th-percentile speed or posted speed limit is less than 60 km/h (35 mph)....." Chapter 6 - Table 6C-2. Stopping Sight Distance as a Function of Speed Another chart. Table 6C-4. Formulas for Determining Taper Lengths Another chart. Table 6E-1. Stopping Sight Distance as a Function of Speed Another chart Section 6F.55 Portable Changeable Message Signs ".....The message panel should have adjustable display rates (minimum of 3 seconds per phase), so that the entire message can be read at least twice at the posted speed, the off-peak 85th-percentile speed prior to work starting, or the anticipated operating speed....." Section 6G.13 Work Within the Traveled Way at an Intersection ".....For work at an intersection, advance warning signs, devices, and markings should be used on all cross streets, as appropriate. The typical applications depict urban intersections on arterial streets. Where the posted speed limit, the off-peak 85th-percentile speed prior to the work starting, or the anticipated speed exceeds 60 km/h (40 mph), additional warning signs should be used in the advance warning area....." Section 6G.16 Crossovers ".....B. Crossovers should be designed for speeds no lower than 16 km/h (10 mph) below the posted speed, the off-peak 85th-percentile speed prior to the work starting, or the anticipated operating speed of the roadway, unless unusual site conditions require that a lower design speed be used....." Table 6H-4. Formulas for Determining Taper Lengths Another table. Chapter 7 - No references to 85th percentile speed. Chapter 8 - No references to 85th percentile speed. Chapter 9 - No references to 85th percentile speed. Chapter 10 - No references to 85th percentile speed. Appendix A1 - No references to 85th percentile speed. ----------------------- In conclusion, none of my questions were answered. Regards, Ed White |
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#52
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"Daniel J. Stern" > wrote in message n.umich.edu... > On Sat, 2 Jul 2005, Ivan wrote: > > > WASHINGTON --The highway fatality rate sank to a record low last year, > > the government estimated Thursday, but the administration and auto > > safety advocates bemoaned an increase in the total number of traffic > > deaths and urged a national focus on seat belt use. > > Uh-huh. Meanwhile, 15 nations are safer than the US in terms of deaths per > thousand vehicles, and nine nations are safer than the US in terms of > deaths for same travel distance - data from the various countries is he > > http://www.scienceservingsociety.com/m/data/USrank.xls Interesting reference. Thanks. > > > The fatality rate slid from 1.48 deaths per 100 million vehicle miles > > traveled in 2003 to 1.46 deaths in 2004. It was the lowest since records > > were first kept in 1966, when the rate was 5.50 deaths. > > Uh-huh. Taking a look at that data, we see that the 2004 death rate (which > translates to 9.1 per billion kilometres) was bested in 2002 by Canada, > Australia, The Netherlands, Finland, Switzerland, Sweden, Norway, and the > UK. The UK and Australian results are particularly interesting, since > those countries have the greatest commonality with North America in terms > of roadway geometries and conditions and (with respect to Australia) > distances. Although Australia is a realtively large country, it is not really like the US in terms of population density. It is even more urbanized than the US (in terms of percentage of population living in urban areas). Although the total land area of Australia is about the same as the lower 48 US states, most of it is practically empty (even more so than the American west). Most people live along the coast in relatively densley populated areas. I am not sure how this affects traffic patterns. I suppose it might be like the east or west coast of the US in terms of traffic. Austrialia also has a much higher percentage of people riding public transist than the US and somewhat lower average traffic speeds. http://www.goldwaterinstitute.org/pdf/materials/95.pdf lists average traffic speeds for different areas. As expected the US has the highest average traffic speed. They used a bar chart to show the comparison. It is not finely divided, so the listing below is just an estimate: Asia - 15.5 mph Australia - 27.5 mph Canada - 25 mph Europe - 19.5 mph US - 31.5 mph This data is fairly old (report was from 2000, data is probably several years older) but I suspect the relative numbers are still valid. If anything, I'd guess average US traffic speeds have increased faster than the rest of the world. Still the US, Canada, and Austrlia are close enough for a valid comparison. http://www.driveandstayalive.com/inf...apita_2003.htm has a chart comparing individual US State's motor vehicle deaths per capita to various countries. The data is a little older (2002/2003) but interesting. The Northeastern US States compare favorably with the best countries in the world. Southern and Western US States have much higher per capitia motor vehicle death rates. The US has one of the highest per capitia motor vehicle death rates in the world. However, we also have the highest number of miles driven per person per year. > I suppose NHTSA does need to put a positive spin on it, though. They can't > exactly say "We're pounding our chests about what a great 'n' groovy job > we're doing, and we're making a lot of noise about how our cars are the > safest and best in the whole wide world, even though it's, um, not true". We also have the highest average speeds. The fact that in many areas marginally competent drivers have no alternatives to motor vehicles is also a factor. Ed |
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