【正文】 rm and shortterm construction detours as well as the diversion of traffic to alternate routes require major planning by traffic ,the issue of security of transportation facilities has e to the creation of facilities and processes for random and systematic inspection of trucks and other vehicles at critical locations is a major challenges ,as is securing major public transportation systems such as railroad ,airport and rapid transit list goes on and point is that traffic engineers cannot expect to practice their profession only in traditional ways on traditional ways on traditional any professional,the traffic engineer must be ready to face current problems and to play an important role in anysituation that involves transportation and/or traffic In order to remain up to date and aware the traffic engineer must keep up with modern developments through membership and participation in professional organizations ,regular review or key periodicals,and an awareness of the latest standards and criteria for professional professional organizations for the traffic engineer include the institute of transportation engineer(ITE),the transportation research board(TRB),the transportation group of the American society of Civi engineers(ASCE),ITS America,and of these provide literature and maintain journals,and have local,regional,and national is a branch of the national Academy of engineering and is a major source o research papers and many engineering fields the traffic engineering profession has many manuals and standard references ,most of which will be referred to in the chapter of this references includeTraffic engineering handbook[1]Uniform vehicle code and model traffic ordinance[2]Manual on uniform traffic control devices [3]Highway capacity manual[4]A policy on geometric design of highways an streets(the AASHTO Green Book)[5]A few of these have had major update and revisions since 2000,including references ,1,3,4 and standards such as these are updated frequently,usually on a 5or10years cycle,and the traffic engineer must be aware of how changes in standards,criteria,methodology,and other aspect will affect the practice of the manuals abound and often relate to specific aspects if traffic references document the current state of the art in traffic engineering,and those most frequently used should be part of the professional39。s personal are also a wide variety of internet sites that are of great value to the traffic sites are not listed here ,as they change of the professional organizations,as well as equipment manufacturers,maintain web federal DOT,FHWA,NHTTSA,and private highwayrelated organizations maintain web entire manual on uniform traffic control devices is available online through the FHWA Web traffic engineering is a rapidly changing field,the reader cannot assume that every standard and analysis process included in this text is current,particularly as the time since publication the authors will continue to produce periodic updates,the traffic engineer must keep abreast of latest developments as a professional In the preface to the second edition of this text,it was indicated that the third edition would be in metric the time ,legislation was in place to require the conversion of all highway agencies to metric units over a short time then ,the government has once again backed off this ,at the current time,there are states continuing to use US units,states continuing to use metric units(they had already converted),and an increasing number of states moving back to US units after conversion to the metric of the key references,such as the highway capacity manual,have been produced in both metric and US unit ,like the AASHTO Green Book,contain both metric and US and US standards are not the standard 12ft lane converts to a standard lane,which is narrower than 12 for a 70mi/h design speed convert to standards for a 120km/h design speed,which are not numerically is because even units are used in both systems rather than the awkward fractional values that result from numerically equivalent is why a metric set of wrenches for use on a foreign car is different from a standard US wrench mere states are on the US system than on the metric system(with more moving back to US units)and because the size of the text would beunwieldy if dual units were included ,this text continues to be written using standard US The profession of traffic engineering is a broad and plex ,it relies on key concepts andanalyses and basic principles that do not change greatly over text emphasizes both the basic principles and current(in 2003)standards and re