Here is a graph showing travel time and distance for travel by a car.

Each of these data points was marked at the beginning or end of a trip made by driving a car.

What I am going to do with these data points is develop a linear formula that relates distance and the time required to travel that distance for a specific type of transportation.

Example: Given two points D miles apart, how many total minutes is the travel time, by car?

Tc = Kc + Mc X D

Tc -- Time in minutes to drive by car.

Kc -- A constant term of minutes.

Mc -- Number of minutes per mile of D distance between points.

D - Distance to travel in miles.

The travel time formula above is very interesting when you have constant values for automobiles and public buses and other modes of personal travel.

- You can talk about the personal economic and time choices the different modes of travel provide.
- You can estimate the time benefits resulting from changes in the transportation system, like "faster buses".