D Factor

Directional split of peak-hour traffic


A empty transit vehicle commute to or from a garage, terminal, or a destination between routes.

Decision-Support System

Computer assessment tool that examines the relationships between land use and transportation.


The transfer of ownership of property in a land development from a private owner to a government. The government is not compelled to accept an offer of dedication and may place conditions on its acceptance.


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

A proprietary Pavement Management System (PMS) used by the Vermont Agency of Transportation (VTrans).

Demand Response

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.


The number of dwelling units or units of nonresidential use that are authorized or planned for a unit of land area.

Department of Environmental Conservation

The Vermont ANR department that administers most of ANR’s regulatory programs plus several voluntary pollution and waste reduction programs (including: air quality, environ-mental assistance, public facilities engineering, geology, environmental permits, solid waste, hazardous waste, surface water quality, water-shed planning, stormwater management, and drinking water supply).

Department of Fish & Wildlife

The Vermont ANR department that manages Vermont’s fisheries and wildlife resources, enforces the state’s hunting and fishing laws, and studies and inventories non-game wildlife species and natural communities.

Department of Forest Parks & Recreation

The Vermont ANR department that operates the State Parks system, manages State forests and natural areas, and provides assistance in the areas of forestry, recreation, and conservation education.

Department of Housing & Community Affairs

The Vermont agency that provides planning technical assistance and oversees housing and community development programs. See 3 VSA 2472

Department of Public Works

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

State agency responsible for coordination, operation, and safety of transportation facilities and services, including; highways, bridges, railroads, airports, etc.


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.

Design & Engineering

Design & Engineering

Design Hour Volume

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 Review Commission

An advisory com-mission established pursuant to 24 VSA 4433 (4).

Design Standard

A minimum or maximum standard prescribed by a bylaw that governs a physical characteristic of a Land Development, Building, or Structure (such as its size or shape).


The place or zone in which a trip terminates.

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.


For the purposes of Act 250, Development is defined by 10 VSA 6001 (3). In the context of Land Development, Development is the division of a parcel into two or more parcels, the construction, reconstruction, conversion, structural alteration, relocation or enlargement of any building or structure, or of any mining, excavation or landfill, and any change in the use of any building or structure, or land, or extension of use of land (24 VSA 4303 (10))

Development Agreement (Improvements Agreement)

A contract between a developer and a government that requires the developer to undertake certain actions (such as construct or install improvements) listed in the agreement according to certain specifications and conditions.

Development Exaction

See Exaction

Development Review Board

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. A municipality may create a DRB to consolidate the functions of a Zoning Board of Adjustment and the subdivision review functions of a Planning Commission (See 24 VSA 4460).

Diesel Multiple Unit

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

Administrative supervisor of regional transportation services or infrastructure.

Diverging Diamond Interchange

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-Crossover Diamond Interchange

See “Diverging Diamond Interchange”. The DCD is distinguished from the conventional diamond interchange in that it combines left-turning traffic with through traffic. This is accomplished by having both left-turn and through vehicles cross over to the opposite sides of the roadway at the ramp terminals.

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.


A carrier service (or charge) for the cartage of shipping containers from a dock to an intermediate or final destination.


A privately owned, constructed, and maintained vehicular access from a public or private street to off street parking or off street loading spaces.

Dwelling Unit

One or more rooms, intended to be occupied by a household as separate living quarters containing cooking, sleeping, and sanitary facilities.

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).