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Safety in Modern Highway Design A Thesis Submitted to The Faculty of iichigan.State Gollege of Agriculture And Applied Science by W. Ross Thompson Candidate for the Degree of Bachelor of Science March 1949 TH E515 C7./ Chapter One Introduction ------------------------ Pages 1 and 2. Chapter Two ‘ Brief History of the Safety Problem - Page 3. ----- . Chapter Three ' Present Status of the Problem ------- Page 4. ----- Chapter Four Planning for Safety ----------------- Pages 5 and 6 Chapter Five Intersections ----------------------- Pages 7-10 --- Chapter Six Other marginal Conflicts (a) Movements to and from Roadside -Page 11 ------ (b) Roadside Parking -------------- Page 12 ...... (c) Shoulder Widths --------------- Page 13 ...... (6-) Side Slopes ------------------- Page 13 ------ (e) Pedestrian Crossings ---------- Pages 13 and 14 Chapter Seven Geometry of Highway Design (a) Traffic Lanes ----------------- Pages 15 and 16 (b) Stripping --------------------- Pages 16- 20 -- (c) Crowns and Alignment ---------- Pages 20 and 21 4d) Curves ------------------------ Page 22 ------- (e) Sight-distance ---------------- Page 22 ------- Chapter Eight Minor Points of Design (a) Guard Rails ------------------- Pages 23 - 25 - (b) Retaining Walls --------------- Pages 25 and 26 (0) Signs and Signals ------------- Pages 26 -32 -- (d) Fences and Snow Fences -------- Pages .«32 and 33 (e) Highway Illimination ---------- Pages 33 and 34 Chapter Nine Standardization by the A.A.S.H.O. --— Pages 35- 37--- Chapter Ten Conclusion -------------------------- Pages 38 - 41. Chapter one Introdu cti on The rise of traffic-accident rates to pre-war levels has become a matter of vital concern to the engineering profession. For many years, engineers have been working to provide vehic- les, roads, and Operational control which would enable the private motorist, the commercial operator, the passenger in public vehicles, and pedestrians to reach their destinations conveniently and safely. The problems of the future, though very much like those of the past, will be complicated by a far greater use of mo- tor transportation than has yet been seen. The problem falls into two general classifications, (1) human behavior, and (2) physical conditions. The second part of the problem is the one the civil engineer is most concerned with, however, thr- ough his development of safety features in design, he has an influence on the first, in that his success in design can make human errors and misjudgements less likely to occur. It has been shown over a period of years, that the dr- iver can contribute practically nothing to the relief of con- gestion and comparatively little to the removal of accidents. Therefore, the major improvements in the transportation sys- tem has come and will come through improving the conditions under which vehicles must be Operated. The objectives of the engineer in attacking the trans- portation problem can be broken down into two divisions: (l) to provide functional design, and (2) control of traffic. -2- It is with these two above mentioned objects that this paper is primarily concerned. Chapter Two A Brief History of the Problem Ideally, the most efficient transportation system is one in which there is a sound balance between the driver, the high- way, and the vehicle. Throughout the history of the automotive transportation, these three factors have alternated. In the beginning, the roadway was ahead of both the Bar and the dri- ver. The cars were mechanically imperfect, and the drivers were not too sure of themselves. With research and mass production the situation changed. The car had improved so much that it quickly absorbed all the advantages the highways had to offer at the time. The drivers were clamoring for more and better highways. This sudden change confronted highway departments with the terrific task of building primary roads and all weather surfaces. The entire engineering profession can well be pro- ud of the fine job they did in solving this problem. Prior to the event of World War 11, the roadways were still not adequate due to high velocities developed by the cars and the increased volume of cars on the roads. The pro- lem today is being solved by new superhighways and advanced methods of traffic control. Chapter Three Present Status of the Problem Pr0gress in.America's Highway Safety Program is measured by the record of deaths and injury. Therefore, let us look at the record complied by the "President's Highway Safety Con- ference for 1948". In 1946, accidents on the streets and high- ways took 33,400 human lives. In 1947, the toll was 32,000. The reduction is very encouraging evidence that highway acc- idents can be curtailed. Safety is the result of effort. To go on with the record. The downward trend continues, during the first seven months of 1948, the number of fatalities had dropped 5% below the same period in 1947. Moreover, the death toll went down while the amount of travel went up. But, the 32,000 deaths of men, women, and children who died in traffic in 1947 must not be taken lightly just because the toll is less than the previous year. Accidents may occur under any set of conditions, but if vehicles, roads, and control pro- cedures and devices are designed to fit conditions of use, and known patterns of hunan behavior, physical conditions will be provided under which accident frequency may be greatly re- duced. The driver is entiled to roads safe for reasonable use. He is also entitled to a factor of safety against the hazards over which he has no control. Among these hazards are: phy- sical features of the highway, such as limited visibility; in- adequate signing; and uncontroled or unrelieved congestion. Chapter Four Planning for Safety The presently existing highways of the United States have been built under sustained pressure to provide a large mileage of improvements to meet demands of rapidly expanding motor vehicle use. A large part of this mileage carries a volume of traffic exceeding that which it was designed to serve; and thousands of miles were constructed for the use of vehicles capable of less speed and smaller and lighter than those wh- ich now use them. Reconstruction of parts of our highway mileage, already obsolete, will require time. While rebuilding to modern st- andards of safety is in progress, the traffic meanwhile con- tinues to increase. Therefore, methods must be found and used to reduce the danger of the obsolete mileage. A good lesson can be found in former highway developement. Roads which are built only for today's traffic needs too often become congested-and accident-ridden long before the actual life of the road is ended. Safety must then begin in planning. Through intensive studies made since 1935 in the nation wide State Highway Planning Survey, it has been found that a very small mileage of roads carries extremely heavy duty tra- ffic densities, with corresponding heavy concentration and accidents. The most serious accident factor on these routes is that of "marginal conflicts", ie intersections, movements to and from the roadside, parking on or too close to the high- way, and pedestrain crossings. -6- The very existence of heavy traffic assures the quick developement of roadside commercial establishments. There- fore, the safety hazards they will eventually cause in go- ing to them and subsequent leaving them must be planned for in advance. Roadside control measures, then become a major plann- ing factor. Without some definite provision neither traffic capacity nor safety can long be assured. Such measures include (1) legal control of access, (2) Marginal land aquistion, (3) land use control, and (4) the aquistion by the highway ag- ency of the right to limit private use of land on the road- Side. Chapter Five Intersections In designing a highway with safety in mind,"the marginal conflict", intersections must be given upmost thought and con- sideration, for intersections not only control the time sav- ing service of a route, but also the accident rate. Both rail- road grade crossings and highway intersections have a tend- ency to reduce traffic capacity. This is due not only to the actual stopping and starting, but also to the general slowing down as a precaution on the driver's part. The ideal solution to the problem arising from intersect- ions would be to eliminate them by constructing grade separ- ations. However except under very favorable topograghic con- ditions, this would be very expensive. In the case of rail- road crossings where two or more main-line tracks are oper- ating, a grade separation is imparative, regardless of traf- fic volumes. In the case of highway intersections with a tr- affic density of 4,000 or more daily, every effort should be put forth to provide a separation. Although, more and more grade crossings are being elim- inated by separations, in most instances it is impractical, therfore, other means must be found and used to rid the high- ways of the hazards they create. One phase of the problem de- pends wholly on aquiring adequate land ajoining the highways at crossings. In this way the obstructions whiwh limit sight distance, such as steep banks, trees etc., standing crops, buildings, parked cars, and billboards can be done away with. ~8- The grade and alignment of the highway at crossings, in or- der to eliminate hazards to safety, should be level or nearly so and the highway should be straight for at least a 1000 ft. at railroad crossings, and 300 ft. on through highways. This difference in unobstucted view is due to the fact that at highway intersections, with proper speed reducing signs, the speed of highway traffic would be less than that of the fast- est train and vehicles can be stopped quicker than trains can. There are four methods in general use today to make in- tersections more adequate. They are as follows: /76. a. F/G.‘ b /Wfl$ C: -9- 0n the preceding page in figures (a)and(b) are shown the most common type of improved intersections. Figure (a) widen- ed pavements, gives two additional lanes for 500 to 500 feet on each side of the intersections. This allows a vehicle which is to make either a right hand or a left hand turn to enter the extra lane leaving the other lane free for traffic going straight through. In figure (b) the intersection has a radii of 500 to 500 feet and requires much more land right-of-way, thus boosting the cost. However, it offers much less chance of collision2and is less expensive to construct than a grade separation. Figures (c)and(d) are modifications of the other two types of intersections and are self-explanatory. From these figures it becomes obvious that when aquiring right- of-way, sufficient land should be obtained to accommodate for additional width at intersections, thus providing not only widened lanes but also uncluttered safe sight distance area. From observation and correspondence, it has been found that the state of New York has a very up to date program on grade separations. In 1947, the highway department of that state had a reserve of completed plans ready for contracts amounting to 500, at a total estimated cost of construction of over 60,000,000. These plans included projects for separ- ating the grades of existing highway-railroad grade crossings, at highway-railroad crossings necessary by the construction of new highways, parkways, and thruways, also by the replac- ement of unsatisfactory existing highway-railroad grade sep- arations structure. This paper is too limited by time to go -10- extensively into clover-leaf and similar grade separation construction, however, at the end of this paper will be found a chart showing the safety value of divided high- ways, and crossings which.will serve the purpose of proof of their high safety value. .359. coca—.302; 9:30.? 1:8 >6330k—Xu .3523...- 30309 ... .3 gotcha}: cam-.9005}... Asp-<5 woos cream to .3390. 10302.09 :3. 30:25 3o: 2: o... «a 09.0.? 2:5 .30.. .ocaqlnhu3nnohaxU so 23222.3 83 1.... Eco. 0.1:... 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The danger of this becomes clear when a situation arises that a vehicle approach- ing from the opposite direction enters the picture. Also, if the parked car is very close to the pavement, alighting or getting into the car from the roadside makes it necessary for the person to be either on the road itself or very near it. I Which brings us to the actual matter of right-of-way. The best width for the right-of-way is largely a matter of judgment and must be determined by the requirements of the particular case. It should be not only large,enough for future widening of the road as traffic increases, but wide enough to control the hazards of parking too near the pavement, the roadside establishments, the building of billboards, the planting of trees, shrubs, etc. With this in mind, it is well to note that there is a noticeable trend toward acquirement of 100 to 200 foot strips along the roadside. The state of Missouri has a table based on average daily traffic: Supplementary System Under 100 Vehicles 60 ft ------ 100 to 400 Vehicles 60 Ft major system Under 400 Vehicles so ft ----- .400-1000— 80-100 foot strip Interstate sttem 1000-2000 Vehicles - 120-220 ft. 2000-3000 Vehicles - 120-220 ft. 3000-5000 Vehicles - 120-250 ft. Over 5000 Vehicles - 150-250 ft. -15- In the design standards for the national system of Inter- state Highways as adopted by the American Association of State highway Officals, the following are recommended: Two lane highways --— minimum 120 ft --— Desirable 220 ft. Divided highways —-- minimum 150 ft --- Desirable 250 ft. Shoulder widths recommendedby the A.A.S.H.O. are: " ex- cept in mountainous topography, shoulders shall be provided clear of road surfacing or pavement for a minimum width of 10 feet, measured to the intersection of the shoulder and side slope planes. Such shoulders shall provide support for stand- ing or disabled vehicles. In mountainous country an effective .shoulder width of at least 4 feet shall be provided. The side slopes shall not be steeper than 2:1 in cuts ex- cept solid rocks or other special soils and on other special material that may justify steeper slopes. On fills of 10 feet or less in height the side slope shall not be steeper than 4:19 From correspondence with the state of Minnesota, it is interesting to note that enough right-of-way is obtained to pro- . vide an area beyond the shoulder for ditches with adequate cross section to provide for snow storage. This would indicate that climate and topography create problems which are special and which must be met in order to have safe highways. The final marginal conflict to be discussed is pedestrian crossings. Pedestrians are particularly hard to control due to the obvious reason that they are free to move in any direction without notice. The only sure way to control them is by using physical structures which would eliminate any choice by them. -14- Tunnels, fences, bridges, sidewalks, and separate levels are examples of such structures that should be used if the ped- estrians are to be protected as well as the motorist. However, since pedestrians create a far greater urban problem than ru- ral, and since this paper is devoted to the study of safety of highways outside of cities, it is sufficient to say that in rural areas where pedestrians walk in considerable numbers along or across a highway which carries moderate to heavy tra- ffic volumes, sidwalks have a high safety value. -15- Chapter Seven- Geometry of Safe Highway Design The geometry of safe highway design includes the prin- ciples of alignment, grade, sight-distances, width of pave- ment and lanes, curves, and various correlatives of these fea- tures. They all have a definite effect on safety of highWays. The volume, composition, and speed of traffic are the three basic features that must be accommodated. None can be neglected without producing hazardous operating conditions. In the past the width of lanes was more or less stand- ardized at 10 feet, but at the present time the trend is to- ward wider widths- 11,12, and 13 feet. Wider lanes result in higher safety. The need for using wider lanes came as a dir- ect result of higher velocities and wider vehicles. It has been found that cars traveling at a moderate speed need at least a 2 foot clearance between cars, and as the speed in- creases the need for a greater clearance becomes a necessity. However, and this is important, there is a limit to the width lanes should be made. By extending the lane-width to more than 12 or 13 feet, the motorist tends to eke out an addition- al lane, thus creating three narrow hazardous lanes out of the intended two. For the greatest safety, rural highways are usually built with an even number of lanes: two, four, six, and eight. The reason for this is obvious. Highways having an odd number of lanes are not as safe as those with an even number of lanes, due to the fact that cars traveling in opposite directions must overtake and pass vehicles in the single central lane, -15- thus causing a situation that is ripe for the most fatal type of accident - head-on-collision. Lane efficiency on multiple lane highways can be increased without resorting to the high cost of alteration. This is done by making outside lanes appear and actually be safe. Several methods are being used to accomplish this. Since motorists tend to shy away from outside lanes when there are objects near the pavement edge, if such objects are removed and the shoulders made stable, motorists can be induced to drive along without the feeling of having to give a wide clearance for their safe- ty. Another good method which has been used in the state of Massachusetts with excellent results, is to take advantage of the motorist's preference for smooth, light colored surfaces by constructing the outside lanes of a three or four lane highway of light colored smooth concrete, and constructing the inside lane or lanes of a rough dark.Macadam. The Macadam.sur- face will cause the tires of the vehicle to rumble slightly. The difference in smoothness and color of the surfaces will cause the driver to seek the light smooth outside lane, thus leaving the inside lane or lanes free for passing and higher speed vehicles. This type of construction has the added safety value of making it easier for the driver to stay in the lanes, for it is easier to follow a distinctive color than it is to drive between painted line striping. This brings up the point of pavement marking. Most lane division is made through this device. Basically,'for the safest roads, unbroken lines should be used where driving aecross the line is hazardous and thus prohibited. Broken lines -17- are used where crossing from one lane into another is permitted under favorable conditions. It has been found and is quite un- iversally adopted that white lines from 4" - 8" are the most visable and effective. The American Association of State High— way Officals standards say that the center line should be pla- ced in the following locations: (a) on the approach to the cre- st of a hill where the clear view ahead is less than 500 feet. (b) on all curves having a radius less than 600 feet or where the clear view ahead is less than 500 feet. (0) and on pave- ments wider than 40 feet. Some states use center lines only at points where over- taking and passing is hazardous. In other states, lines are used entensively on straight level stretches as aids for keep- ing traffic in lanes as well as where it is dangerous to be in the lane where traffic from the opposite direction is. This is by far the better practice, for it takes the human element out of the picture to some degree. The procedure recommended by the A.A.S.H.O. is to have a broken white line 15 feet in length with a 25 foot gap, a shorter line and gap tends to give an annoying flickering sensation which induces fatique. A yellow solid line has been found to be most effective as a regulatory line used where it is unsafe and therefore illegala to cross. It is recommended because it contrasts with the white line, used where it is not prohibted to cross, and thus. gives emphasis to the existing hazard. Also, since yellow has been more or less adopted universally as a symbol for warning signs and signals, it becomes apparant,just seeing the color warns of danger. -18- The state of New York and others, however,use broken white lines in combination with solid white lines to mark the " no passing" areas. They have a very good reason for not following the standard. Yellow paint can not be disting- used from white at night or during rainstorms. This would in- dicate that more study should be done on the standard color to be used. The chart of United States that follows shows the 48 states' procedure. It can be noted from this map that the st- andard is not followed very closely throughout the states. The center lines themselves can be constructed from the material used to fill the joints if it is of contrasting color, or inserts can be used. The state of Kansas and Texas, also, use this method. It has a very good feature, in that when one passes over these inserts a very slight rumble is noted, thus if the driver unconciously crossedJit will be brought to his attention. Letters from several states indicate their center line striping method and in some cases why they use what they do. Quoting from a letter from the state of Wyoming, " In the item of center line marking, we use a solid barrier line with brok— en center line- 15 foot stripe and 25 foot skip. We use a yellow color for both lines. Yellow traffic paint is a mag: in Wyoming, as it contrasts with snow and in our state there are sections of roads at different locations that are subject to snow every month of the year. In color we vary from the nat- ional standard and feel that our reasons are sound. The design of stripe and skip are standard: we use a 4" line in case of double marking, a 4" spacing between stripes is usedE 1" MAP SHOWING METHODS or mam-4C. CENTER LINE mo NO msswc. mus m ALL or me sun-cs or ‘ “SH: 1H: UNITED surcs AND THE PROVINCES or owmwo "079 TON mo oucecc 'N CANADA . ¢ . ‘_ ‘000 I r.E ll ' ' ‘ M'~~CSO T :' «3 n... A Pnovwccs or omamo & oucacc .1 ya 5 . 8 °° H—iK‘; _lll‘ 0.41%.qu ' . t 3 ~ I I .5395 ‘ : ‘ é . :I s 5 f ‘3 ' ' 3 1 1| : .. ‘ " - L ’ N4 NEW I t I W‘CO OKLAHOMA 4.000 3 a s , :l 3 i : S 3 1‘ . 1 I. f... S TEXAS ' I 1 :§ ‘Ili I I ? NQYE STAYE DEPT 0" PUBLIC WORKS ‘ CHARLES H SELLS. SUPCRINTENMNY I an": uul I“ ' “n'” . I“ ' "A" no noun no nu 00ml 0! f:t?.'$f1°§£‘£2.‘£3721£‘.“°32 '3:‘.‘.‘.I$2.""°‘ "‘ ° ' mu . u-va. mm m. m .... 00- anon on um: ton com- nua- on mm: (on Hanna. ::'mu';la.:n0¢::uru:v.:vm‘ -19- From the New Hampshire Highway department: "Practically all the narrow two lane pavements have a center stripe of yellow paint, six inches in width. On wider pavements, strip- ing is confined more to curves and such portions of the high- way as have restricted vision. Some experiments have been car- ried on with reflectorized paint. To date, however, in climate like ours which over several months of the year requires snow removal, we do not find the same to be durable or worthwhile? From the State of Wisconsin: " For a year or two during the war when paint and manpower were scarce, we did not place pavement markings on some of our state trunk highways which had previously had been marked. As a result, we had numerous complaints and we have concluded that pavement markings are an important activity and that its lack is equally noticeable to the traveling public. As a result, we have reestablished the policy of placing center lines on all pavements having a reasonable life. It is probable that we will follow the rec- ommendations as to color, width of line, and type of marking which.the A.A.S.H.O. has s andardized." The State of Rhode Island reports: " We use a solid 6" white line on two lane highways regardless of the type of pave- ment and hope some day to treat the hazardous vertical and horizontal curves where sight distance is limited with a 4" white barrier stripes. On four lane highways we use the double center line which consists of two 4" stripes with a 5" separ- ation with the side lane stripes eliminated on concrete pave- ments. We like the reflectorized line very much indeed, but on some of our heavily travelled two lane highways, we have PLAN NO PASSING ZONES SIGN SUMMIT ON CENTER LINE HIGHWAY oouo'r cnoss RED SHOULDER LIN? +/— LINE IN YOUR LANE ‘ I CONCRETE . PAVEMENT 2 —_—/|_ —————— -___~—_--— -—_—_—_————-—--——-- SIGN SHOULDERLINE DO NOT CROSS RED LN NE IN ram/\fi’l YOUR LANE PLAN No PASSING LINE -- % PERsIAN RED '1} LEGEND CENTER LINE - BLACK A, “Neat" PAVEMEM‘WO PASSING LINE- PERSIAN REo g CEEIEZKL'NE I‘" BRICK PAVEMENT ----- “"7“ “"5 “A % NO PASSING LINE- 'WHITE “In CENTER LINE- WH TE % No “53mg “NE .‘I BLACK 7°” SURFACE ” No RAssINC LINE- PERSIAN RED PERSIAN REo I} NOTE- CENTER LINES ON CONCRETE AND BRICK PAVEMENTS TO BE SOLID BLACK LINES CENTER LINE ON BLACK TOP SURFACE TO BE A BROKEN WHITE LINE SUMMIT DETAIL or MARKINGS AT SUMMIT CONCRETE PAVEMEN I SIGN ELEVATION \fi\\ ' \ 'IH‘I‘. ...; ~'-.,' ..V‘ .. ~- II _ '\ ' \.”_nll, u” 0". VI-.“, ‘HL \14, V , 0.. V " " M\I I < r‘_. ‘ ‘l‘ :1, ‘1. \u \H. 1'?” .” “I’av;'\ " \ ' ' W " v 4 VHI’I’W ‘ 1‘ K ' “53mm C ., V1- .,_ l V\ p. \o \‘Hw‘ ‘\u” 9;!IIV"V ‘ (:2? \ C I I ’I :NZ‘L’.’ V. \\l’ V‘. \"‘— I V I; . V \ 4 . ‘3’”! 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N . zoEszr— ”um—Em Run—(m.— —# NOT TO SCALE 930 9.3.5 .0 .3 uuéd =9.-- iludaooa 3 fl S. U PIC—m O._. mum! "E. .38 8:38: swam; w m w a M w a m M DIVISION OF HIGHWAYS III .JCZOEhO .OZ 20:..ng no 1:0qu 10:215. Ugh mom; M80 D... .mme..vN 0 82gb”. 8min ..m _-.-H r.... -.-- APE—mm; 33m ”+8? .5974 :0 33.33 0:: .~ 3.8 O :33 .mH. IIIIII IJIIII .. .. I... ..... ....I In . . . ... la. ,.o.. . . O . I I ....I ‘u.o... -20- used the paint with glass beads exclusively." Over a period of years, it has been found that the great- est safety value in center lane separation of a four lane high- way can be obtained from physical barriers. This virtually el- iminates the most serious type of accident - the-head-on-col- lision. There has been a great deal of research on this part~ icular method of separation. Michigan has about 300 feet of medial barrier designed by the Yale Traffic Bureau under test. Many four lane highways are constructed with a boulevard type of separation. The value of this type of barrier is increased if low planting is done to eliminate glare from on coming cars. Woodward Avenue is an excellent example of a multiple lane highway with low planting. Other features of highway design considered from the stand- point Of safety are crowns and superelevations of curves. Al- though, crowns are not Of major importance in comparison with other phases of design with safety in mind, it must be noted, however, that if the surface of a roadway were made level ac- ross the road, rain water and melting snow would not run off, thus causing the highway to be slippery and dangerous when wet. The crown or difference in elevation between the center and the edges of a road depends on the type of surface used. It is ob— vious that water will run off more readily from a smooth con- crete surface than from a rough one. Eor high type surfaces a crown Of l/8th of an inch.per foot has been found to be suff- icient. The crowned surface is generally curved to the shape of a parabola. In laying out the crossection of a highway it is necessary to obtain elevations of the surface at different -21- points, using a parabolic surface, this verticle distance of any point below a horizontal line tangent to the roadway sur- face at the center is computed as follows: Y: igéi : c(“')2 W 2 szverticle distance of point below tangent at center of road in inches. 0: crown of road in inches. X: horizontal distance to point from center line of roadway in feet. W: width of roadway in feet. Example: the concrete pavement 40 feet wide is to have a crown of 1/8 inch per foot of half-width. If a parabolic crown is used, to find the ordinate from the tangents at the center surface at a point 5 feet from center. Sclution: C: 1/8 X 20 3 2.5 in at 5 feet from center. - 2 2 . Y- 40% a 4x25; x § § 4 x 2.5 x 25 : 0.156 in '_’I660 The ideal alignment for safe design would be a perfectly straight road between two points at grade. This would elimin- ate all vertical and horizontal curves and the resulting dan- gers they entail. Of course this is not only impossible but not desirable because it would be tiresome to drive. There- fore, the radius of the numerous curves that are necessary to fit a highway line into its natural surroundings has an important bearing on the safe driving speed and sight-dis- -22- tances of the road. The present standards set limiting, minimum radii for curves that are, for the most part, greater in len- gth than previously used. The outer edge of the pavement it- self is elevated in varying degrees depending on the length of radius Of the curve. If this relationship is worked out care- fully it will actually facilitate steering around the curve, eliminate the need for a quick recovery coming out of the curve, and cause only a very slight awareness of any superelevation. The degree Of superelevation must not be so great as to cause lateral slipping toward the center when a slower speed is used during rainy or icy weather. The following computations and illustrations will serve as examples to the reader on how vertical and horizontal curves, and sight-distances are worked out in design. A word should be said about sight-distances. Vertical sight-distance is the distance at which a driver, who is sitting in a vehicle with his eyes assumed to be about 5 feet above the pavement, can see a corresponding point or another car. This distance on a straight level road is about eleven miles, and is limited by the earth's curvature. Horizontal sight-distance is a similar measure in which the limiting ob- struction would be found along the side of the highway on the inside Of the curve. This could be the shoulder of a bill, a building, or trees. Vertical and horizontal sight-distances are computed for every foot of highway constructed. «arm—4024. ZO.FUquuO 444.3% aOL m>m30 no IFOZM... 23—2—22). .23. a .12;er E «Bounce... crmvuo Riofiooos co >33... .52.: 9. .O.I.m.<.< 5 332.83% .oom ..n .000 -.v .00» .m .oom .N .oom ._ I. Q a...» awn... “DumD mm QJDOIW mm>m30 m0 mIFOqu 3.33.2.5 02:30.30m NIP mmqoz< ZOfiUmgme 44.435 up“. ><>>IO_I MI... 2. {22 4 m0 wUZ< Oh 9-2. 295$ 22me 22. 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However, no matter what material they are made from, they must be a protection and act as a warning. To be effective and lend safety to the motorist, they are used wherever the highway is on an embankment and the side slopes are steeper than 1 vertical to 3 horizontal, or on any section of a highway where the motorist needs this added pro- tection. Their main function is to prevent a vehicle from lea- ving the highway in case the operator loses control of the ma- chine. The ideal guard rail should deflect the vehicle back to- ward the roadway rather than check its speed or stop it. Also the guard rail should be constructed in such a manner as not to entangle the vehicle, but to allow it to slide freely along the face of it. It is impractical to construct a guard rail with sufficient strength to stop a fast-moving car quickly.If the guard rail stopped, within 1 or 2 feet, a vehicle that struck it at high speed, the damage caused would be almost as great as if the vehicle had gone over the embankment. Other design.features of a guard rail should include low enough height so as to come in contact with the bumper and the wheels of the car, any other part of the vehicle, such as the hood, would crush.easily under impact. They should be highly visible and not be constructed so as to cause snow to drift in their locality. Wooden guard rails were used extensively during the horse .and buggy days. They still are used to some extent where lum- her is plentiful. The disadvantage of the wood type is that lumber of small cross-sectional area has a low resistance to Shock and when struck will damage the vehicle. However, if heavy planks are used, say 3 x 10 inches and larger, this dis- advantage will be overcome to a great degree. Steel cable railings usually consist of 3/4 inch wire tape mounted on wood posts, steel posts, and masonry posts. Although low in cost to build, they are difficult to see. Also they sag with weather changes; and they actually don't give too much protection when struck. If spring tightening devices and off—set lugs, to hold the cable away from the post, are used, this decreases the last two mentioned disadvantages to some degree, while durable white paint will increase their Visibility. Wire mesh guard rails are usually from 14 to 22 inches wide and are usually palced on wood posts. They have several advantages; they don't cause too much damage when hit; they are strong and tend to deflect cars back to the roadway when struck; and when painted white they are very easily seen. The disadvantage of using them is when struck the section must be -25- replaced, also they tend to act as snow fences in snowy re- gions. There are several types of steel plate guard rails us- ed today. Some are directly connected to posts, while others have spring connections giving greater deflection. They cause little damage to the vehicle when struck and are easily seen. However, they too act as snow fences in snow areas. Masonry railings are not used very often, except where appearance is important. They make a very neat looking rail, and need not be painted. Guard rails demand special treatment. They must be kept painted to maintain their visibility effectiveness; and they must not be placed so as to become hazards themselves. Since guard rails make parking on the shoulders impossible and since guard rails make mowing and maintaining the shoulders diffic- ult, sometimes other construction would be better employed, such as making the slope 4 horizontal to 1 vertical. In.unusa1 cases gravity retaining walls, which depend on their own weight for stability, are needed in highway constru- ction. However, they are rarely needed over 18 feet in height. They provide safety by stablizing the slope and thus keeping the soil off the road surface. This of course would lend saf- ety by preventing skidding caused from mud from the slope, and losing control of the vehicle by striking rocks and other such objects that had rolled onto the highway. Retaining walls are usually built in.monolithic sections of 20 to 25 feet in len- gth; expansion joints are provided between these sections. The expansion joints may consist simply of a plane of weakness -26.. between the sections, produced by allowing one section to set before building the adjacent wall; or it may be a key joint. Another phase under minor points in design is signs and signals which is an important part of any highway system. Si- gns and signals have an essential place in the safety of a highway. Their design and installation has become quite well standardized through the efforts of the American Association of State Highway Officals. Highway signs may be classified as: route markers; guide series; informational series; regulatory series; warning series; and caution series. As the speed of the vehicle has increased and as the vol- ume of traffic has increased, traffic control devices have be- come more necessary for warning and guiding traffic. Intersec- tions are the most critical points in traffic control, espec- ially where two primary routes cross. However, excessive use of signs to warn of hazards, signs to indicate traffic regul- ation, and the misapplication of control devices not only wa- stes the public's money, but has in many cases accomplished the reverse of the intention, causing delay, confusion, and disrespect for and disregard of all control devices. Traffic control requirements in any specific case cannot be determined byfiguess work. They should be based on sound en- gineering principles established by factual studies of acci- dents, speeds, physical conditions, and delay. In this way the problems can be understood and subsequently solved with the result of safety to the motorist. Modern highway speeds and complex intersections require signs which can be seen at long distances and understood in- -27- stantly. This calls for simple standardization. The following characteristics of signs have been standardized and made simple to provide uniformity of significance in the signs themselves, and to make familiarity with them easy to aquire even by the most causual driver: (a) application (d) location (g) wording (b) shapes (3) diminsions (h) lettering (0) colors (f) symbols (1) illumination The first series to be discussed is route markers. The great advantage to tourists in having continuous route numbers across the states is quite obvious. At the time this system was established, each of the numerous trail associations had its own distinctive marker and, in many cases, several such ass- ociations used the same highway throughout varying distances. A situation demanding correction was thus created. Some of these trail associations made very fine contributions to the highway improvement program. Others did much more harm than good, for sometimes one section of a road might carry as many as eight different sets of route markers. Over 25,000 miles of uniformly marked roads in the United States highway system has done away with all this confusion. The standard route marker for all U.S. highways is a shield bearing the name of the state across the top and below the let- tering U.S., followed by the route number. The design is black on a white background. These shields are used only in marking U.S. highways. In general, highways marked with odd numbers run nor- th and south, while those with even numbers run east and west. various types of markers are used for state routes in the different states. Several states, including Arkansas, Illinois, I 5 . .""' '1“ on" .' " ..., 7"_ £14. .‘1 " 33-1- -« ".74; 0;.- ”‘5; VJ .K‘JWWIMh’ In '.T7' 7“." T':TBV:-Hw H‘. ‘, I .. ' .. . « «- ..- . . - . . rm W‘MJ.& V'fi . ._... u- . riff: éLJIml limn—‘oV-(Q‘LERJ' S'v‘ 5? .744 - :‘ '51.: .25. (-5 .....aoHv-w'fi — "—w‘" w“, ‘ ”7:1". . 7:73;. .12; i Y: In Jill..- fl. 1 u .34 GUIDE FEDERAL MARKER SERIES us M-1 U. S. ROUTE Shield Regulation shield for marking of all federal routes. Mount on one steel post, or special steel frames. (Refer to ”Sign Assemblies "Standard Types” for details of erection.) M-SZ u. s. ROUTE Shield Special shield for limited use in urban areas where space does not permit use of regulation size. AP- proval for use must be granted by main office. Mount on one steel post, or special steel frames. M-3 U. S. ROUTE Shield Special shield for limited use in urban areas where space is restricted. Approval for use must be grantecl by main office. Mount on one steel post, or special steel frames. M-4 FAS Marker Use at beginnings and ends of Federal Aid road projects off the regular federal Aid System, such as NRS, \X/PS, \X/PGS and FAGS projects. It is necessary that the project number be shown but not the prefix letters. Indicate directions by use of the small arrow. Mount on one wooden post on the north side of East-\X/est highways and on the east side of North-South routes. (Refer to ”Sign AS- semblies—Special Types” for details of erection.) M-S FAP MARKER Use at beginnings and ends of Federal Aid road projects on the regular Federal Aid System, such as FAP, NRH, \X/PGH and FAGH projects. It is necessary to show the project number but not the prefix letters. Indicate directions by use of the small arrow. Mount on one wooden post on the north side of East-\X/est highways and on the east side of North-South routes. (Refer to "Sign Assemblies- Special Types” for details of erection.) :04. o . .. . 0 f. s¢.‘9.'.?’. . s u . u a . s .v . . . i a} ll ”.ludlu j CI. .IE|I ...PI :1. nir‘ . b . . .. "‘ .-.. .j . .. I J 1. . . I g“ . I “3. a“ Jfl-II I e \ _.. a n ' 1. a t ... u .. 6 i1 3"! ..Q . .‘\ 1 I“... 9.. V o a . CO”. 1.-., 4 O D... I. o O . “O 0". 0V.' ....“I o. HO. O 'n’.. O O 00' 0.0.. o I . ...... 0.”..ricn. ... I~ ..IC. 0 -5! O “.0... .Ot’t 0 O ... oOJJJ§JOtJN§II u .5 Eli. 0.1.... u o e I n J: ... u ..r o. n . . . v 1......v .w! u. .. . . . a. I. . . 0 . .. ..i ... ... . .. . . . . a n... u u u o s t o . O a a . . . I. o . . a 0 0 0 - in“ . .-J O 0 p G U l D E STATE MARKER SERIES M-10 COLE COUNTY M15 M-10 STATE ROUTE Marker Use on all State numbered routes. Mount on one steel post, or special steel frames. (Refer to ”Sign Assemblies—Standard Types" for details of erection.) M-15 SUPPLEMENTARY ROUTE Marker Use on all supplementary lettered routes. At county lines erect supplementary markers for each direc- tion of travel indicating the county to be entered. Mount on one steel post, or special steel frames. (Refer to "Sign Assemblies—Standard Types" for details of erection.) -28- Missouri, Ohio, and South Dakota use-the state outline bear- ilug the route number as a distinctive marker. Some states use nuxrkers such.as a covered wagon in Nebraska, the conventional swuxflower in.Kansas, the indian head in North Dakota, and the 'triangle in.Wisconsin. The U.S. markers should always be placed at intersections vflsere a motorist is likely to become confused, such as: at all :right angle intersections; at all intersections where the route inrrns; at all irregular intersections, such as a "T" or "Y": at all intersections where the type of road surface changes. Chi straight, open stretches of a U.S. numbered highway, add- itional markers placed at one and one-half mile intervals help the motorist considerably. State route markers should be Tised in similar cases. Informational signs are used to give locations, distances, speed limits, cities on a route, etc. They are of value to the motorist, but do not relate to the immediate or detailed con- trol of the vehicle. The standard shape is rectangular. They are usually black symbols or letters on a white background and are bordered in black for higher visibility. ( see illus- trations) Directional signs are those which give information nec- essary to the operation of the vehicle. There are two groups of this type; those requiring readiness to act, for example: school zone. These are square in shape and are usually black on a federal yellow background. The second group includes con~ ditions for definite action, for example: curve. The standard EEEEEEEEEEEEEEEEE >ELnuN 21 e> boa FESTUS # Rig t Directional Guide BUSINESS " DISTRICT G—b Left Business District MEXIBD I7 BOWLING GREEN BI LOUISIANA 72 G-1 RIGHT FINGERBOARD G-2 LEFT FINGERBOARD Use at Class B junctions to inform traffic of the direction and distance to various destinations (See ”Sign Assemblies—Fingerboard Erection" for details). For restricted use at important intersecting roads with marked routes, by indicating directions only towards points along intersecting roads. A max- imum of two fingerboards for any given direction will be permitted. Fingerboards with black arrows shall be used to indicate numbered lal03#> N¢~NCD+D 48 56 19 12 12 51 50 0 PrOperty Damage 5875,545 24,955 67,250 40,275 29,8671 15,220 47,684 64,500 8,285 12,504 8,987 8,489 16,067 55,445 52,800 Accidents per 100 Million Vehicle Niles 595 562 452 750 440 548 284 615 505 789 505 297 180 746 450 564 260 452 1,154 765 557 258 85 201 97 57 206 200 205 Fatalities 100 Million Vehicle Miles 11.2 14.5 18.8 C>-fl . 7‘ design speed are minimum and should be considered for use when lhcy Minimum & Desirable Speed Al 0 -- ll D M 0 Al D M D M D ll 0 make possible an appreciable reducrion in consfrucfion cosf. ln Flaf 45 55 f 45 55 50 60 60 6‘5 65 70 55 70 55 70 general more desirable standards should be used. Design Speed in Al.P.H. Rolling 35 45 ’ 35 50 50 55 55 60 55 60 ll- is permissible 10 change design speed wilhln a single projecf Mounfainous 25 35 I. 25 40 40 40 40 50 40 50 if fopogr‘aphy indicates SuCh proceedure will result in economy in ‘ ‘ ' ‘ 'l f' . Non—P0551ng Sight 0151‘. Flaf . 475 cons ruc ion (4.5 Fl. at 4- ’nCh) Rolling I i- 350 For supp/emen'lary roads carrying over 400 vehicles per day use major sysfem standards. cc w“. -~. a”), P ; -_-__ ~ 9 Mounfa inous 275 Passing 3596* 0151*. Flat f' 2l00 0n major and infer-stare systems grad/81115 of 7% may be used in ° ' 'i h r1 1h 1. (4.5 Ff. & 4.5 Fl.,provm’e Rolling . I400 s or eng 5 on y of leasf once every 2 miles) 900 CW and fill slopes are To be modified in stable and semi-sfable Materials. (See lypical sections.) Mountainous Flar Gradients Rolling corner, shorter radius may be used. . 11.. a --._-~‘Q~*-_ —- . Mountainous Flat . Curve lure Rolling ---.1 , ' 7 5 5 *In Special cases such as school house or cemefery in section 6 5 $0r1 infersfal‘e system fill slopes shall not be sieeper fhan 4:!, and minimum (0’ shoulder widfhs are required. «-— .. _ ”._...—”._.-- . 4 MOLN7ral770US N”_ 7”“‘ - I] [I ~ ll "H“ -77” m- 7 7 I .. Dual Roads:- When average daily traffic 3f fime 0f C005frujt - f; : lion exceeds 3000 vehicles per day, secore R/W for dual construc ion, Surface Widfh (Min. 8. Range) . l8 - 22 22 . 44 When traffic exceeds 5000 vehicles pe’” day. consider inlfial dual Roddbed Width (Min. & Range) 7 _ ... 25‘ - 38 #- 38 - 42 80 - [03 consfrucl'ion. Righf of way 1111.111. Min. 1. Range) 80 - 100 120 . 220 120 - 220 120 - 250 150 - 250 Media, gym-p w,'dfh5;- ' 1 ) 3:1 nder 10‘ :1 d 10' 3: . :1 . .. 1 1 Min. 15'; DeSIrab/e 40‘. RUM” - U ® un er ,_,_____, _..-linger ’0 Uhdel‘ ’0 3 I Under 0 Min. 4‘; DESIFab’e [2". (Urban) 2:1 over 10'® :1 over 10' 2:1 over 10' .- over 10* 2:1 over 10' : 0' : ' - :‘~ 1 . 1 Urban Area Sfandards:- : {under ’10 CC?) : underipfii“ under ’01” 52d“ ’0 4" under ,0 11m. Design speed 40 11.10.11,; Desirable 50 M.P.H. : over ' . . Over l0” Z:l over l0' : over l0' 2i, over l0’ , May. Curvature I40 In Slopes (IllaiL steeper than) : ‘ : 3;] 4:, 4., 4:, 4,, Min, Non—Passing Sighf Dishince 275' . . ' .1 . . Min, Passing Sight Distance 900' Deplh of Dlrch (Min. below shoulder) - 2 2 2 2 2 Min Lane Width ,2. Cut Slopes (Nof sleeper fhan) Fill Slopes {Not sleeper than) SP"" Curves ”one On all Curves over 2°-00' ” ‘ . . "Rounding of slopes' and Compacting by Railing requ1red only 'ldfh 22; To be deformined by Bridge Bureau when using Major sysl’em standards. "Machine Grading" and "Linear Bridges (New) . Loading . H-li5 ‘ Mile Grading" permifrec' only when using supplementary sfandards. Bridges (Use in place) Width 1"]5 -, To be defer-mined by Bridge Bureau These slope: apply for Major Sysfem roads only. Sieeper slopes ‘ Loading 6T- ‘_ permitted for Supplemenfary roads. 0-531 (5'-12' 59063} , C~528 (5'*12' 50003} I - .9 (ff-12 Evans} 1 f bl‘ h' 1 rl’ ln fhs normal roadbed width and normal l 801: Culvert Standards 0—532 (2'41 Spars.) , 0-530 (2.4. Spans/ 2350 (2.4. Scans] slopesnsgjl‘i bésusizgocu ve eg 0-31 (Skeyilpf f C—27 (Skew) 0-27 (Skew) For Cross—Road StWCt- 12" to 84" Incl. N'd-lldwls. 15” to 48” Incl. C-ZBOR lldwls. 15" to 48" Incl. 0-230 Hdwls. i For Struct. under Appr's. 12" to 84" Incl. Momma} 12" to 84” Incl. No lldw‘ls. 12" to 84" Incl. No lldwls. P ”ive Culverts for Dual Lane i ,- . 1. I .: 's‘ " i- ‘ ‘3 I lyrical Section Dwg.# 1 AC _154c .1; 1 AB 1 AB or.144 1 AB or 114 1 AA '4‘ 0' 5.... Spam forgg,; O I 1' P'os '- —'.._ ' VV‘*‘-”““;""‘!'I'j'"'_ wry- v con-1 3 03177 4106 IQ. 12 3 i | 0"... v'l‘ ..‘o.‘..0 O 9.. -11" . 1‘...O . V... g