Transportation Glossary

The following is a listing of transportation-related terminology and phraseology developed by CCMPO.
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Term	Acronym	Definition
Deadhead		A empty transit vehicle commute to or from a garage, terminal, or a destination between routes.
Decision-Support System	DSS	Computer assessment tool that examines the relationships between land use and transportation.
Deflection		A horizontal change in the travel path of traffic due to a physical feature of a roadway. An example would be a "Splitter Island" of a roundabout. Here traffic is slowed by a geometric curvature (or deflection) from a straight trajectory before entering a channelized approach into the roundabout.
Deighton Total Infrastructure Management System	dTIMS	A proprietary Pavement Management System (PMS) used by the Vermont Agency of Transportation (VTrans).
Demand Response	DR	A transit mode comprised of passenger cars, vans, or small buses operating in response to calls from passengers or their agents to the transit operator, who then dispatches a vehicle to pick up the passengers and transport them to their destinations. A demand response (DR) operation is characterized by the following; 1. Vehicles do not operate over a fixed route or on a fixed schedule except on a temporary basis to satisfy a special need, 2. Vehicles may be dispatched to pick up several passengers at different pick-up points before taking them to their respective destinations and may even be interrupted en route to these destinations to pick up other passengers.
Demand Response Service		Shared use transit service operating in response to calls from passengers or their agents to the transit operator, who schedules a vehicle to pick up the passengers to transport them to their destinations.
Department of Public Works	DPW	Municipal entity responsible for repair and maintenance of streets, sewers, greenspace, and urban landscape. DPWs also designs and manage the construction of public facilities.
Department of Transportation	DOT	State agency responsible for coordination, operation, and safety of transportation facilities and services, including; highways, bridges, railroads, airports, etc.
Design & Engineering	D&E	Design & Engineering
Design Hour Volume	DHV	Commonly (but, not strictly) the 30th highest hourly traffic volume for a given year. DHV has been considered to be an optimal traffic volume estimation for designing future transportation infrastructure (e.g. intersection and roadway capacity analysis, bridge design, and geometric specifications, et al.) since the 1950 release of the Highway Capacity Manual (HCM).
Design-Build	D-B	Design-Build (D-B) is an efficient method to complete transportation projects, where designer engineers and construction contractors are brought together under a single contract. This contrasts to the traditional "Design-Bid-Build" (D-B-B) approach where two different contracting efforts must be undertaken in sequentially; 1. Obtaining engineering services on a negotiated-price basis, and 2. Obtaining construction services on the lowest-responsible-bid price basis.
Destination		The place or zone in which a trip terminates.
Destination Choice		An estimate of a trip endpoint determined by a combination of the purpose and origin of the trip. Destination choice is believed to depend on characteristics of the individual (income, auto ownership), characteristics and location of activities at which the trip’s purpose can be accomplished, and characteristics of transportation modes connecting the origin to each possible location.
Detectable Warning		Standardized surface feature built into pedestrian or transit-related infrastructure, which is designed to warn visually impared pedestrians of changes in curbline, slope, crossings, etc. It is generally a tactile standardized feature, intended to function much like a stop sign. It alerts perceivers to the presence of a hazard in the line of travel, whereupon they would stop, and determine the nature and extent of the hazard, before proceeding further.
Development Review Board	DRB	Development Review Boards are quasi-judicial, citizen volunteer bodies created under Vermont Statute 24 VSA Chapter 117, intended to interpret and uphold zoning ordinances of their municipality.
Diesel Multiple Unit	DMU	Self-propelled railcar, powered by one or more diesel engines.
Discretionary Funds		Funds whose distribution is not automatic and not by formula but dependent on the decision of some agency or party.
Distracted Driving		A specific type of inattention that occurs when drivers divert their attention away from the driving task to focus on another activity instead. These distractions can be from electronic distractions, such as navigation systems and cell phones, or more conventional distractions such as interacting with passengers and eating. These distracting tasks can affect drivers in different ways, and can be categorized into the following type; 1. Visual Distraction - Tasks that require the driver to look away from the roadway to visually obtain information; 2. Manual Distraction - Tasks that require the driver to take a hand off the steering wheel and manipulate a device; 3. Cognitive Distraction - Tasks that are defined as the mental workload associated with a task that involves thinking about something other than the driving task. The impact of distraction on driving is determined not just by the type of distraction, but also the frequency and duration of the task. That is to say, even if a task is less distracting, a driver who engages in it frequently or for long durations may increase the crash risk to a level comparable to that of much more difficult task performed less often. Because drivers often have a choice regarding when and how often to multitask when driving, their exposure to risk is typically within their control; however NHSTA research has shown that drivers underestimate the overall risk of various tasks.
District Transportation Administrator	DTA	Administrative supervisor of regional transportation services or infrastructure.
Diverging Diamond Interchange	DDI	A variation on a "Diamond Interchange", a DDI (also known as the "Double Crossover" intersection) increases safety by reducing the number of potential conflict points of traffic. The DDI accommodates left-turning movements at a signalized, grade-separated interchanges of arterials while eliminating the need for left-turn signal phasing. On an arterial (i.e. a high-volume road), traffic crosses over to the left side of the roadway between the nodes of the interchange. Two-phase traffic signals are installed at roadway crossovers. Once vehicles are on the left side of the arterial roadway, they may turn left onto limited-access ramps without stopping or conflicting with through traffic.
Double-Stack Railcars		Rail-freight configuration allowing double-stacking of shipping containers-on-flat-cars (COFC) during transport. Operation of such a configuration can be hindered by clearance restrictions on rail lines.
Drayage		A carrier service (or charge) for the cartage of shipping containers from a dock to an intermediate or final destination.
Dynamic Striping		A traffic calming technique using experimental systems of pavement markings, which is not yet mandated by the Manual on Uniform Traffic Control Devices (MUTCD).

OTHER TRANSPORT TERMINOLOGY REFERENCES: