Appendix F Glossary
The following is a list of some commonly used terms in transport modelling and their definitions.
| Accessibility | An indication of the proximity of a person, site or zone to a particular activity or group of activities. It is also defined as the ease or difficulty of making trips to or from each zone. |
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| Aggregate data | Data that relates to a mass of group of people, vehicles or area. The collective properties of the variable are of interest. |
| AON assignment | The AON (all-or-nothing) assignment technique by which minimum travel time paths are computed for each zone pair and all flows between these pairs are loaded onto these paths. |
| Capacity restraint | A traffic assignment technique that takes into account the build up of congestion with increased traffic volumes. It adjusts the link travel times according to the prevailing flows. |
| Centroid connector | Imaginary links that represent the street network within a zone. They ‘connect’ trips from a zone to the modelled network. |
| Destination | The point or area of termination of a trip. |
| Disaggregate data | Data at the level of individual persons, households, etc. |
| Employment | The number of employees, or jobs, in relation to the zone of work. This may be stratified by employment type e.g. retail, manufacturing, etc. |
| External trip | A trip that has either an origin or destination, but not both, in the study area. |
| Equilibrium assignment | An assignment process by which all used routes between zone pairs have equal and minimum costs, while all unused routes have greater or equal costs. |
| Generalised cost | This cost is usually a linear additive function of some, or all, of the following costs: travel time between zones, access and wait times, ride time, distance between zones, fares, fuel costs and parking charges. |
| Gravity model | A model that distributes the number of trips between all trip-producing zones and trip-attracting zones. |
| Home | A group of rooms or a single room, occupied or intended for occupancy as separate living quarters by a family, group of persons or by a person living alone. |
| Home-based trip | A trip that has its origin or destination at the home end. It may be a person trip, vehicle trip, walk trip, or public transport trip. |
| Household | A person or persons living in the one home. |
| Incremental assignment | The process by which flows between all zone pairs are loaded onto the network in pre-specified steps. |
| Internal trip | A trip that has both its origin and destination in the study area. |
| Link | A section of a highway or public transport network defined by a node at each end. |
| Logit model | Also known as the ‘multinomial logit model’, it calculates the proportion of trips that will select a specific mode or activity. |
| Minimum path | The route between a zone pair that has the least cost (time, distance, generalised) in comparison to all other possible routes. |
| Minimum path tree | All the minimum paths between zone pairs that emanate from an origin zone. |
| Modal split | The division of trips between different modes of travel (private transport, public transport). |
| Node | A numbered point on a network representing a centroid or a junction of two or more links. |
| Non home-based trip | A trip that has neither origin nor destination at the home end. It may be a person trip, vehicle trip, walk trip, bicycle trip or public transport trip. |
| Origin | The point or zone at which a trip begins. |
| Person trip | Any trip made by a person. |
| Screenline | An imaginary line, usually along physical barriers such as rivers, railway lines or roads. Screenlines split the study area into a number of parts. Traffic classification counts, and possibly interviews, may be conducted along these lines to compare or calibrate data and models. |
| Travel time | The time taken to travel between two points. |
| Trip | A one-way movement from an origin to a destination for a particular purpose. It may be a person trip, a vehicle trip, walking trip or public transport trip. |
| Trip assignment | The process by which flows between zones derived from the trip distribution process are allocated to the minimum path routes through a network. |
| Trip attraction | Usually used to describe trip ends connected with non-residential land uses in a zone. Also defined as the non home end of a home based trip or the destination of a non home based trip. |
| Trip distribution | The process by which the total numbers of trips originating in each zone are distributed among all the possible destination zones. |
| Trip end | Either a trip origin or trip destination. |
| Trip generation | The process by which the total numbers of trips beginning, or ending, in a zone are determined, based on demographic, socio-economic and land use characteristics. |
| Trip matrix | A two dimensional matrix that represents the demand for travel among all zones in a study area for individual or grouped purposes, modes or types. |
| Trip production | Usually used to describe trip ends connected with residential land uses in a zone. Also defined as the home end of a home-based trip, or the origin of a non home-based trip. |
| Trip purpose | This can be defined as work trips, school trips, recreational or social trips and shopping trips. |
| Zone | A portion of the study area with homogenous land use, socio-economic and demographic characteristics. |
| Zone centroid | An assumed point in a zone that represents the origin or destination of all trips to or from that zone. Generally, it is the weighted centre of trip ends, rather than the geometrical centre of a zone. |