Use the interactive applet for visual understanding of speed time graphs.
This applet can model any given text problems of up to 5 distinct parts of a total journey.
You can use the ShowViewScaleControls to modify the scale and views of the axes, and values. The horizontal is in time units (you can set it to seconds, minutes or hours), and the vertical is in units per time unit so you can set it to metres or kilometres per time unit (depending on your x axis units)
This resource is downloadable from Geogebra Tube at http://tube.geogebra.org/material/show/id/YpTfUB6Z