  A time-space traffic (TS) diagram, which presents traffic states in
time-space cells with color, is an important traffic analysis and visualization
tool. Despite its importance for transportation research and engineering, most
TS diagrams that have already existed or are being produced are too coarse to
exhibit detailed traffic dynamics due to the limitations of existing
information technology and traffic infrastructure investment. To increase the
resolution of a TS diagram and enable it to present ample traffic details, this
paper introduces the TS diagram refinement problem and proposes a multiple
linear regression-based model to solve the problem. Two tests, which attempt to
increase the resolution of a TS diagram 4 and 16 times, are carried out to
evaluate the performance of the proposed model. Data collected at different
times, in different locations and even in different countries are employed to
thoroughly evaluate the accuracy and transferability of the proposed model.
Strict tests with diverse data show that the proposed model, despite its
simplicity, is able to refine a TS diagram with promising accuracy and reliable
transferability. The proposed refinement model will "save" widely existing TS
diagrams from their blurry "faces" and enable TS diagrams to show more traffic
details.
