Ways of measuring the transport of goods and people
The units of measurement in transportation describes the unit of measurement used to express various transportationquantities, as used in statistics, planning, and their related applications.
vehicle-kilometre (vkm[1]) as a measure of traffic flow, determined by multiplying the number of vehicles on a given road or traffic network by the average length of their trips measured in kilometres.[2]
vehicle-mile (vehicle miles traveled, or VMT[1]) same as before but measures the trip expressed in miles.
Passenger-distance is the distance (km or miles) travelled by passengers on transit vehicles; determined by multiplying the number of unlinked passenger trips by the average length of their trips.
passenger-kilometreorpkm internationally;
passenger-mile (orpmi?) sometimes in the US; 1 pmi = 1.609344 pkm
A system may carry a high number of passengers per distance (km or mile) but a relatively low number of passengers per bus hour if vehicles operate in congested areas and thus travel at slower speed.
A transit system serving a community with a widely dispersed population must operate circuitous routes that tend to carry fewer passengers per distance (km or mile). A higher number is more favorable.
Freight is measured in mass-distance. A simple unit of freight is the kilogram-kilometre (kgkm), the service of moving one kilogram of payload a distance of one kilometre.
Asemi truck traveling from Los Angeles to Chicago (approximate distance 2,015 miles) carrying 14 short tons of cargo delivers a service of 14 * 2,015 = 28,210 ton-miles of freight (equal to about 41,187 tkm).
Intermodal container traffic is commonly measured in twenty-foot equivalent units (TEUs), rather than cargo weight, e.g. a TEU-km would be the equivalent of one twenty-foot container transported one kilometer.[6]
Transportation density can be defined as the payload per period, say passenger / day or tonne / day. This can be used as the measure of intensity of the transportation on a particular section or point of transportation infrastructure, say road or railway. This can be used in comparison with the construction, running costs of the infrastructure.
Fatalities by VMT (vehicle miles traveled) is a unit for assessing road traffic fatalities. This metric is computed by dividing the fatalities by the estimated VMT.
Usually, transport risk is computed by reference to the distance traveled by people, while for road traffic risk, only vehicle traveled distance is usually taken into account.[7]
In the United States, the unit is used as an aggregate in yearly federal publications, while its usage is more sporadic in other countries. For instance, it appears to compare different kind of roads in some publications as it had been computed on a five-year period between 1995 and 2000.[8]
In the United States, it is computed per 100 million miles traveled, while internationally it is computed in 100 million or 1 billion kilometers traveled.
According to the Minnesota Department of Public Safety, Office of Traffic Safety
Volume of traffic, or vehicle miles traveled (VMT), is a predictor of crash incidence. All other things being equal, as VMT increases, so will traffic crashes. The relationship may not be simple, however; after a point, increasing congestion leads to reduced speeds, hanging the proportion of crashes that occur at different severity levels.[9]
MacNeal 1994[10] discusses the history of this topic, exploring such units and how humans developed the current state of logically recognizing and naming them.
