Legibility studies of dynamic message signs

[Pink Jazz]

Just as there have been studies for ways to improve the legibility of normal signs (fonts, retroreflectivity, etc.), I was wondering, could we in the future see studies on the legibility of dynamic message signs?  While DMS are subject to technological advances, there is still a lot of inconsistency between different DOTs and manufacturers.  For example, for on-freeway use ADOT only recently started to install full matrix DMS after many years of sticking with fixed character matrix models.  I presume the reason for the switch is probably due to declining manufacturer support for fixed character matrix models, thus ADOT probably wanted to get more bids and better pricing, which Skyline Products won.  Still, the full matrix models are being programmed in a fixed character style, probably since ADOT is still using the existing software to control all of its DMS to maintain compatibility with the older models.

I presume that any legibility study would probably favor full matrix DMS models over fixed character matrix or row matrix DMS.  There would probably be a recommended dot pitch and character size as well.

What does anyone here think?

[roadfro]

If there aren't at least some existing studies on the topic, I'd be surprised... There should be.

I don't know that fixed matrix versus full would me the subject of a study on legibility, rather the size of lettering involved (regardless of position on the sign) and lighting elements/conditions.

[Pink Jazz]

If there aren't at least some existing studies on the topic, I'd be surprised... There should be.

I don't know that fixed matrix versus full would me the subject of a study on legibility, rather the size of lettering involved (regardless of position on the sign) and lighting elements/conditions.

I know fixed character matrix signs limits the width of all characters to a monospaced font, compressing normally wide characters such as "M" or "W".  Also, both fixed character matrix and fixed row matrix limits character height.

In addition, I think fixed character matrix signs are poor at displaying mixed case text.  Perhaps such studies would also determine whether or not DMS messages should be in mixed case or in all-caps.

[roadfro]

I guess I interpreted "fixed matrix" as merely a character positional issue (as in fixed lines, etc.), not relating to the size/width of individual characters... In that case, I don't know that there has been much study performed since I don't know that such displays are widespread.

[Pink Jazz]

I guess I interpreted "fixed matrix" as merely a character positional issue (as in fixed lines, etc.), not relating to the size/width of individual characters... In that case, I don't know that there has been much study performed since I don't know that such displays are widespread.

There are indeed some DMS models with fixed lines, which are known as row matrix models.  Row matrix DMS use long matrices that are divided into two or three rows for text. They allow variable character spacing, but limit character height. 

Fixed character matrix DMS, on the other hand, use individual matrices that are equally sized and spaced for each character, only allowing a monospaced font.

[Scott5114]

This is one of those things where new technology is outpacing the guidelines for using it. Full matrix VMSes are widespread in some areas but some regions have yet to adopt it (I think I've seen a grand total of one in the entire state of Oklahoma, and that one was using the same amber lighting that the fixed-matrix ones do). The new signs let us do a lot more things that we couldn't do with the old ones, so this is all new stuff that needs to be studied.

I would hazard a guess that if new guidelines are ever released, they endorse usage like Minnesota's and Florida's, where a non-variable sign is graphically replicated on the VMS. The FHWA fonts are a safe bet for legibility if they can be accurately replicated (i.e. very little aliasing), especially since you don't have to worry about halation from retroreflective sheeting.

[vtk]

This is one of those things where new technology is outpacing the guidelines for using it. Full matrix VMSes are widespread in some areas but some regions have yet to adopt it (I think I've seen a grand total of one in the entire state of Oklahoma, and that one was using the same amber lighting that the fixed-matrix ones do). The new signs let us do a lot more things that we couldn't do with the old ones, so this is all new stuff that needs to be studied.

I would hazard a guess that if new guidelines are ever released, they endorse usage like Minnesota's and Florida's, where a non-variable sign is graphically replicated on the VMS. The FHWA fonts are a safe bet for legibility if they can be accurately replicated (i.e. very little aliasing), especially since you don't have to worry about halation from retroreflective sheeting.

As I understand it, halation occurs in the eye, so it could also happen with an emissive source like a VMS if the sign is significantly brighter than anything else in the driver's field of view.