# transportation

## The speed of spacetime

For each mode of travel there are four speeds to consider: the minimum speed, the typical speed, the maximum speed, and the speed of particular objects. The more that impediments to travel are removed (e.g., other objects, the topography, the network), the more that speed reaches free flow. In transportation, the free flow speed is …

## Actual and default speeds

The actual speed of a particle or vehicle is the local conversion of duration and distance, that is, local time and space. The potential speed of a particle or vehicle is a characteristic speed for similar particles or vehicles. This characteristic speed is a default speed, to be used if the actual speed is not …

## Time at Mach 1

In a sense every speed is a conversion speed, that is, a way to convert time into space and vice versa because multiplying a time interval (duration) times the speed of an object leads to the corresponding space interval (length). In some contexts, i.e., a transportation mode or physical medium, there is a particular speed, …

## Converting space and time

To convert a length of space into a corresponding length of time requires a conversion factor. For physical reality that conversion factor is the speed of light: r = ct, where r is a spatial displacement, t is a temporal displacement, and c is the conversion factor. For a mode of transportation the conversion factor …

## Actual and potential time and space

I’m made the point that if we’re asked how far away a place is, we can answer in units of space or time. If we’re talking about stable places such as on land, the distance will not change but the length of time depends on a characteristic speed. In that case the length of time …

## Equality of space and time

“How far is it to X from Y?” That everyday question can be answered either by a distance or a duration with a mode of travel (e.g., walking, driving, flying). The interchangeability of a length of space and a length of time leads to two simple conclusions: (1) time has as many dimensions as space …

## Kinds of relativity

A simple way to look at the world is to assume that space and time are absolute: the locations, the distances, the durations, speeds, and so forth as measured by one person are the same for everyone. That is, if my automobile speedometer shows 50 mph (80 kph), then the police with a laser gun …

## Lorentz interpreted

The question is how to interpret the Lorentz transformation. In a previous post, Lorentz generalized, a modest generalization of the Lorentz transform was derived. Absolute reference speeds were combined with a relative actual speed. Let’s step back and look at a map of space and time: This map of nodes and links on the U.S. …

## Lorentz generalized

In some ways transportation is more general than physics, which is surprising. In terms of extent, from the microscopic to the astronomical, from extremes of temperature, etc., physics is the more general subject. But because transportation includes people, there are some additional possibilities. Let’s look at one transportation situation in which this is the case. …