DesignElementDefinitions-Maine.gov.docVIP

FHWA Design Element Definitions (/geometric/pubs/mitigationstrategies/) DS- Design Speed Design speed is a selected speed used to determine the various geometric features of the roadway.? The assumed design speed should be a logical one with respect to the topography, anticipated operating speed, the adjacent land use, and the functional classification of the highway. Design speed is different from the other controlling criteria in that it is a design control, rather than a specific design element.? In other words, the selected design speed establishes the range of design values for many of the other geometric elements of the highway LW- Lane Width The adopted criteria describe design values for through travel lanes, auxiliary lanes, ramps, and turning roadways. There are also recommended widths for special-purpose lanes such as continuous two-way left-turn lanes. ?AASHTO also provides guidance for widening lanes through horizontal curves to provide for the off-tracking requirements of large trucks. Lane width does not include shoulders, curbs, and on-street parking areas. SW- Shoulder Width Shoulders provide a number of important functions.? Safety and efficient traffic operations can be adversely affected if any of the following functions are compromised: Shoulders provide space for emergency storage of disabled vehicles.? Particularly on high-speed, high-volume highways such as urban freeways, the ability to move a disabled vehicle off the travel lanes reduces the risk of rear-end crashes and can prevent a lane from being closed, which can cause severe congestion and safety problems on these facilities. Shoulders provide space for enforcement activities.? This is particularly important for the outside (right) shoulder because law enforcement personnel prefer to conduct enforcement activities in this location.? Shoulder widths of approximately 8 feet or greater are normally required for this function. Shoulders provide space for maintenance activities.? If routin