1.4 Basic Concepts in Traffic EngineeringnMobility versus Accessibility（机动性和可达性） nHighway Classification （道路分类） nUninterrupted （连续流）and Interrupted （间断流）flows nResponsibility and Liability (责任与义务)nTransportation Legislation (交通立法)nMobility (机动性) - refers to the ability to travel to many different destinations, while accessibility (可达性) - refers to the ability to gain entry to a particular site or area With an increase of mobility the ability to access development decreases, and vise versa. Mobility versus AccessibilityGraphic description between mobility and accessibilityHighway classification nLocation - urban and suburban (rural)nCriterion - specification for roadway designnEach country has different way in determining hierarchy of highwaysThe purpose of conducting classification for highway is to clarify the functionality of each category of roadways in providing services in terms of mobility and accessibility With increase of mobility the accessibility will decrease Freeway has the highest mobility; whereas local street has thehighest accessibilitynFreeways or expressways - access-controlled, multilane, divided highways devoted to high-speed, long-distance travel with little or no access adjacent to landnArterials - roadways serving primarily to move traffic between principal traffic generators with partially access-controlled (residential access is discouraged, but commercial access is allowed), there are two categories: major and minornCollectors - roadways serving internal traffic movements within an urban area and connecting it with the arterial system, there are two categories: major and minornLocal streets - primarily providing access to the development with low-speed Uninterrupted and Interrupted flowsnUninterrupted flow (连续流)facilities have no external interruptions (外部干扰) to the traffic stream. Pure uninterrupted flow exists mainly on freeways and expressways.nInterrupted flow (间断流) facilities have external interruptions to the traffic stream. Almost all urban surface streets and highways are interrupted flow facilities. Uninterrupted flow facilities are fully or partially access-controlledFreeway in Germany (2008)Expressway in Beijing (2007)Interrupted flow facilities are not access-controlled, with external disruptions,resulting in stop-and-goUrban street in Atlantic City, USAUrban street in BeijingResponsibility and LiabilitynPublic safetynLegal obligation - legal casenCommunication (沟通)with people traffic engineers work for - public hearing (听证会) public involvement (公众参与)nCommunity protection - traffic calming （宁静交通）Leeds, EnglandDresden, GermanyLane reduction is one oftraffic calming strategiesTransportation Legislation of USAnFederal-Aid Highway Act (1916 to 1983) （联邦公路法） nIntermodal Surface Transportation Efficiency Act (ISTEA) from 1991 to 1997 (冰茶法案) nTransportation Equity Act for the 21st Century (TEA-21) from 1998 to 2004 (二十一世纪交通法案)nSAFETEA-LU （Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users 2005 to 2011）