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Safe Routes to School (SRTS) [program]
A federally funded grant program intended to increase the number of children safely walking and bicycling to and from school. Projects include infrastructure improvements (sidewalks, traffic signals, pavement markings, etc.) and noninfrastructure activities (education and encouragement programs).
SAFETEA-LU (Safe, Accountable, Flexible, Efficient Transportation Equity Act:
A Legacy for Users)
The federal surface transportation legislation (Public Law 109-59) that authorizes programs for highways, highway safety and transit for the five-year period 2005-2009.
safety hangers
Backup for original bridge or structural connections to provide redundancy; often added for seismic retrofit.
Safety Management System
A systematic process that has the goal of reducing the number and severity of traffic crashes by ensuring that all opportunities to improve highway safety are identified, considered, implemented as appropriate and evaluated in all phases of highway planning, design, construction, maintenance and operation; and by providing information for selecting and implementing effective highway safety strategies and projects.
scissors off-ramp
A condition where one-way traffic streams cross by merging and diverging maneuvers onto exit ramps; drivers tend to go straight ahead onto an off-ramp instead of turning left.
Secondary Roadway System
Noninterstate roads.
selective attention
The ability, on an ongoing moment-to-moment basis while driving, to identify and allocate attention to the most relevant information, especially embedded when within a visually complex scene and in the presence of a number of distracters.
shared roadway
A type of roadway where bicyclists and motor vehicles share a travel lane.
short line
An independent railroad company that operates over a relatively short distance.
sight distance
The length of highway visible to the driver.
sight triangle
In plain view, the area defined by the point of intersection of two roadways, and by the driver's line of sight from the point of approach along one leg of the intersection, to the farthest unobstructed location on another leg of the intersection.
single-occupancy vehicle (SOV)
This term refers to vehicles that are carrying one person.
situational awareness
The selective attention to and perception of environmental elements within a specified space and time envelope, the comprehension of their meaning and projection of their status in the near future.
slip ramp
A diagonal ramp, more properly called a cross connection, which connects with a parallel frontage road.
small target visibility (STV)
A proposed criterion for roadway lighting; the concept assumes that increased target visibility results in both increased nighttime safety and improved nighttime driver performance; a surrogate for reduced accident risk.
smog
A general term used to describe irritating haze produced by photochemical reactions in the atmosphere.
span
The distance between bridge piers, towers or abutments.
special mobile equipment (SME)
Off-highway equipment incidentally operated on highways.
speed
Design speed is the maximum safe speed that can be maintained over a specified section of highway when conditions are so favorable that the design features of the highway govern. The design speed of a roadway dictates which geometric design standards are used such as stopping sight distance, radius of curves, and banking (superelevation) of road surfaces.

Operating speed is the speed at which drivers are observed operating their vehicles.

Posted speed is the maximum speed limit posted on a section of roadway using a regulatory sign.
speed-change lane (SCL)
Used in the interchange/ramp exit models; it refers to the speed-change maneuver on deceleration lanes segmented components.
sprawl
A haphazard and disorderly form of urban development; there are several elements that characterize a sprawl.
stable
Able to resist forces that can cause material deformation or structural collapse.
Statewide Transportation Improvement Program, Iowa (STIP)
A two-year program of transportation projects required by SAFETEA-LU, consisting of a federally required document that allocates transportation funds to a staged, multiyear, statewide, intermodal program of transportation projects; consistent with the statewide transportation plan and planning processes and metropolitan plans, TIPs and processes; the metropolitan TIP must be included in the STIP without change.
stay
Diagonal brace installed to minimize structural movement.
steel
A very hard and strong alloy of iron and carbon.
steering control (SC) zone
Used with interchange/ramp entry traffic models; it is the zone where positioning of the vehicle along a path from the controlling ramp curvature onto the speed-change lane is accomplished.
stopping sight distance (SSD)
The sight distance required to permit drivers to see an obstacle soon enough to stop for it under a defined set of reasonable worst-case conditions, without depending upon speed, gradient, road surface and tire conditions, and assumptions about the perception-reaction time of the driver.
stranded shoe
The device at the end of an eye-bar that holds the wires of each strand for the main bridge suspension cable; the strands loop around the shoes to form a continuous cable from anchorage to anchorage.
stringer
A longitudinal beam supporting the bridge deck.
Structure Inventory and Appraisal Rating (SI & A)
A 0-100 rating indicative of a structure’s sufficiency to remain in service (0 worst – 100 best); this is a federal rating measure based on a structure’s structural adequacy, safety, serviceability, functional obsolescence, and essentiality for public use.
strut
A piece or member acting to resist compressive stress.
study area
A geographic area selected and defined at the outset of engineering or environmental evaluations, which is sufficiently adequate in size to address all pertinent project matters occurring within it.
study (or project) limits
The physical end points of a proposed project or study, usually designated at geographic or municipal boundaries, at interchanges, at roadway segments where cross sections change, or at the beginning or end of numbered state traffic routes.
subdrains
Used to assist in controlling ground water under roadway pavements and various applications.
substructure
The parts of a bridge that are below water or land; the piers, or tower foundations and anchorages.
Superpave (Note capital "S" "Superpave" - complete title: SUperior PERforming Asphalt PAVEments)
An asphalt mixture designed to resist the rutting and fatigue cracking caused by heavy loads and extreme temperatures, as experienced with the previous standard.
superstructure
The parts of a bridge that are above water or land; the towers, main cables, suspender cables and related parts.
supplemental appropriation
An act appropriating funds in addition to those in an annual appropriation act because the need for funds is too urgent to be postponed until enactment of the next regular appropriation act.
suspended span
A simple span supported from the free ends of cantilevers.
suspender cables
The vertical wires are hung at regular intervals connecting the main bridge suspension cables to the deck; the connection is made using a cable band.
suspension bridge
A bridge in which the floor system is supported by tow cables that are supported upon towers and are anchored at their ends.
switching
Movement of freight cars between two nearby locations or trains; switching is a term typically associated with activities that occur in a railcar classification yard or terminal.